.github/workflows/build-and-test.yml

@@ -9,28 +9,14 @@ on:
 jobs:
   build-ubuntu-gcc:
     runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        version: [12]
     steps:
       - uses: actions/checkout@v4
-      - name: Setting up gcc version
-        run: |
-          sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-${{ matrix.version }} 100
-          sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-${{ matrix.version }} 100
       - name: Build
         run: make test
   build-ubuntu-clang:
     runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        version: [14, 15]
     steps:
       - uses: actions/checkout@v4
-      - name: Setting up clang version
-        run: |
-          sudo update-alternatives --install /usr/bin/clang++ clang++ /usr/bin/clang++-${{ matrix.version }} 100
-          sudo update-alternatives --install /usr/bin/clang clang /usr/bin/clang-${{ matrix.version }} 100
       - name: Build
         run: CC=clang CXX=clang++ make test
   build-musl:

Android.bp

@@ -73,9 +73,6 @@ cc_library {
         debuggable: {
             cflags: ["-DLABEL_MEMORY"],
         },
-        device_has_arm_mte: {
-            cflags: ["-DHAS_ARM_MTE", "-march=armv9-a+memtag"]
-        },
     },
     apex_available: [
         "com.android.runtime",

CREDITS

@@ -54,230 +54,3 @@ libdivide:
 
 random.c get_random_{type}_uniform functions are based on Fast Random Integer
 Generation in an Interval by Daniel Lemire
-
-arm_mte.h arm_mte_tag_and_clear_mem function contents were copied from storeTags function in scudo:
-
-    ==============================================================================
-    The LLVM Project is under the Apache License v2.0 with LLVM Exceptions:
-    ==============================================================================
-
-                                     Apache License
-                               Version 2.0, January 2004
-                            http://www.apache.org/licenses/
-
-        TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
-
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README.md

@@ -159,9 +159,6 @@ line to the `/etc/ld.so.preload` configuration file:
 The format of this configuration file is a whitespace-separated list, so it's
 good practice to put each library on a separate line.
 
-On Debian systems `libhardened_malloc.so` should be installed into `/usr/lib/`
-to avoid preload failures caused by AppArmor profile restrictions.
-
 Using the `LD_PRELOAD` environment variable to load it on a case-by-case basis
 will not work when `AT_SECURE` is set such as with setuid binaries. It's also
 generally not a recommended approach for production usage. The recommendation
@@ -473,16 +470,16 @@ was a bit less important and if a core goal was finding latent bugs.
     * Errors other than ENOMEM from mmap, munmap, mprotect and mremap treated
       as fatal, which can help to detect memory management gone wrong elsewhere
       in the process.
-* Memory tagging for slab allocations via MTE on ARMv8.5+
+* [future] Memory tagging for slab allocations via MTE on ARMv8.5+
     * random memory tags as the baseline, providing probabilistic protection
       against various forms of memory corruption
     * dedicated tag for free slots, set on free, for deterministic protection
       against accessing freed memory
+    * store previous random tag within freed slab allocations, and increment it
+      to get the next tag for that slot to provide deterministic use-after-free
+      detection through multiple cycles of memory reuse
     * guarantee distinct tags for adjacent memory allocations by incrementing
       past matching values for deterministic detection of linear overflows
-    * [future] store previous random tag and increment it to get the next tag
-      for that slot to provide deterministic use-after-free detection through
-      multiple cycles of memory reuse
 
 ## Randomness
 
@@ -724,48 +721,77 @@ freeing as there would be if the kernel supported these features directly.
 
 ## Memory tagging
 
-Random tags are set for all slab allocations when allocated, with 5 excluded values:
+Integrating extensive support for ARMv8.5 memory tagging is planned and this
+section will be expanded to cover the details on the chosen design. The approach
+for slab allocations is currently covered, but it can also be used for the
+allocator metadata region and large allocations.
 
-1. the default `0` tag
+Memory allocations are already always multiples of naturally aligned 16 byte
-2. a statically *reserved free tag*
+units, so memory tags are a natural fit into a malloc implementation due to the
-3. the previous tag used for the slot
+16 byte alignment requirement. The only extra memory consumption will come from
-4. the current (or previous) tag used for the slot to the left
+the hardware supported storage for the tag values (4 bits per 16 bytes).
-5. the current (or previous) tag used for the slot to the right
 
-When a slab allocation is freed, the *reserved free tag* is set for the slot.
+The baseline policy will be to generate random tags for each slab allocation
+slot on first use. The highest value will be reserved for marking freed memory
+allocations to detect any accesses to freed memory so it won't be part of the
+generated range. Adjacent slots will be guaranteed to have distinct memory tags
+in order to guarantee that linear overflows are detected. There are a few ways
+of implementing this and it will end up depending on the performance costs of
+different approaches. If there's an efficient way to fetch the adjacent tag
+values without wasting extra memory, it will be possible to check for them and
+skip them either by generating a new random value in a loop or incrementing
+past them since the tiny bit of bias wouldn't matter. Another approach would be
+alternating odd and even tag values but that would substantially reduce the
+overall randomness of the tags and there's very little entropy from the start.
 
-This ensures the following properties:
+Once a slab allocation has been freed, the tag will be set to the reserved
+value for free memory and the previous tag value will be stored inside the
+allocation itself. The next time the slot is allocated, the chosen tag value
+will be the previous value incremented by one to provide use-after-free
+detection between generations of allocations. The stored tag will be wiped
+before retagging the memory, to avoid leaking it and as part of preserving the
+security property of newly allocated memory being zeroed due to zero-on-free.
+It will eventually wrap all the way around, but this ends up providing a strong
+guarantee for many allocation cycles due to the combination of 4 bit tags with
+the FIFO quarantine feature providing delayed free. It also benefits from
+random slot allocation and the randomized portion of delayed free, which result
+in a further delay along with preventing a deterministic bypass by forcing a
+reuse after a certain number of allocation cycles. Similarly to the initial tag
+generation, tag values for adjacent allocations will be skipped by incrementing
+past them.
 
-- Linear overflows are deterministically detected.
+For example, consider this slab of allocations that are not yet used with 15
-- Use-after-free are deterministically detected until the freed slot goes through
+representing the tag for free memory. For the sake of simplicity, there will be
-  both the random and FIFO quarantines, gets allocated again, goes through both
+no quarantine or other slabs for this example:
-  quarantines again and then finally gets allocated again for a 2nd time.
-  Since the default `0` tag isn't used, untagged memory can't access malloc allocations
-  and vice versa, although it may make sense to reuse the default tag for free
-  data to avoid reducing the possible random tags from 15 to 14, since freed
-  data is always zeroed anyway.
 
-Slab allocations are done in a statically reserved region for each size class
+    | 15 | 15 | 15 | 15 | 15 | 15 |
-and all metadata is in a statically reserved region, so interactions between
-different uses of the same address space is not applicable.
 
-Large allocations beyond the largest slab allocation size class (128k by
+Three slots are randomly chosen for allocations, with random tags assigned (2,
-default) are guaranteed to have randomly sized guard regions to the left and
+7, 14) since these slots haven't ever been used and don't have saved values:
-right. Random and FIFO address space quarantines provide use-after-free
-detection. We need to test whether the cost of random tags is acceptable to enabled them by default,
-since they would be useful for:
 
-- probabilistic detection of overflows
+    | 15 | 2  | 15 | 7  | 14 | 15 |
-- probabilistic detection of use-after-free once the address space is
-  out of the quarantine and reused for another allocation
-- deterministic detection of use-after-free for reuse by another allocator.
 
-When memory tagging is enabled, checking for write-after-free at allocation
+The 2nd allocation slot is freed, and is set back to the tag for free memory
-time and checking canaries are both disabled. Canaries will be more thoroughly
+(15), but with the previous tag value stored in the freed space:
-disabled when using memory tagging in the future, but Android currently has
+
-[very dynamic memory tagging support](https://source.android.com/docs/security/test/memory-safety/arm-mte)
+    | 15 | 15 | 15 | 7  | 14 | 15 |
-where it can be enabled/disabled at any time which creates a barrier to
+
-optimizing by disabling redundant features.
+The first slot is allocated for the first time, receiving the random value 3:
+
+    | 3  | 15 | 15 | 7  | 14 | 15 |
+
+The 2nd slot is randomly chosen again, so the previous tag (2) is retrieved and
+incremented to 3 as part of the use-after-free mitigation. An adjacent
+allocation already uses the tag 3, so the tag is further incremented to 4 (it
+would be incremented to 5 if one of the adjacent tags was 4):
+
+    | 3  | 4  | 15 | 7  | 14 | 15 |
+
+The last slot is randomly chosen for the next allocation, and is assigned the
+random value 14. However, it's placed next to an allocation with the tag 14 so
+the tag is incremented and wraps around to 0:
+
+    | 3  | 4  | 15 | 7  | 14 | 0  |
 
 ## API extensions
 

androidtest/Android.bp

@@ -1,25 +0,0 @@
-java_test_host {
-    name: "HMallocTest",
-    srcs: [
-        "src/**/*.java",
-    ],
-
-    libs: [
-        "tradefed",
-        "compatibility-tradefed",
-        "compatibility-host-util",
-    ],
-
-    static_libs: [
-        "cts-host-utils",
-        "frameworks-base-hostutils",
-    ],
-
-    test_suites: [
-        "general-tests",
-    ],
-
-    data_device_bins_64: [
-        "memtag_test",
-    ],
-}

androidtest/AndroidTest.xml

@@ -1,13 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<configuration description="hardened_malloc test">
-
-    <target_preparer class="com.android.compatibility.common.tradefed.targetprep.FilePusher">
-        <option name="cleanup" value="true" />
-        <option name="push" value="memtag_test->/data/local/tmp/memtag_test" />
-    </target_preparer>
-
-    <test class="com.android.compatibility.common.tradefed.testtype.JarHostTest" >
-        <option name="jar" value="HMallocTest.jar" />
-    </test>
-
-</configuration>

androidtest/memtag/Android.bp

@@ -1,16 +0,0 @@
-cc_test {
-    name: "memtag_test",
-    srcs: ["memtag_test.cc"],
-    cflags: [
-        "-Wall",
-        "-Werror",
-        "-Wextra",
-        "-O0",
-    ],
-
-    compile_multilib: "64",
-
-    sanitize: {
-        memtag_heap: true,
-    },
-}

androidtest/memtag/memtag_test.cc

@@ -1,297 +0,0 @@
-// needed to uncondionally enable assertions
-#undef NDEBUG
-#include <assert.h>
-#include <malloc.h>
-#include <signal.h>
-#include <stdio.h>
-#include <stdint.h>
-#include <stdlib.h>
-#include <sys/utsname.h>
-#include <unistd.h>
-
-#include <map>
-#include <set>
-#include <string>
-#include <unordered_map>
-
-using namespace std;
-
-using u8 = uint8_t;
-using uptr = uintptr_t;
-using u64 = uint64_t;
-
-const size_t DEFAULT_ALLOC_SIZE = 8;
-const size_t CANARY_SIZE = 8;
-
-void do_context_switch() {
-    utsname s;
-    uname(&s);
-}
-
-u8 get_pointer_tag(void *ptr) {
-    return (((uptr) ptr) >> 56) & 0xf;
-}
-
-void *untag_pointer(void *ptr) {
-    const uintptr_t mask = UINTPTR_MAX >> 8;
-    return (void *) ((uintptr_t) ptr & mask);
-}
-
-// This test checks that slab slot allocation uses tag that is distint from tags of its neighbors
-// and from the tag of the previous allocation that used the same slot
-void tag_distinctness() {
-    // 0 and 15 are reserved
-    const int min_tag = 1;
-    const int max_tag = 14;
-
-    struct SizeClass {
-        int size;
-        int slot_cnt;
-    };
-
-    // values from size_classes[] and size_class_slots[] in h_malloc.c
-    SizeClass size_classes[] = {
-        { .size = 16,    .slot_cnt = 256, },
-        { .size = 32,    .slot_cnt = 128, },
-        // this size class is used by allocations that are made by the addr_tag_map, which breaks
-        // tag distinctess checks
-        // { .size = 48,    .slot_cnt = 85,  },
-        { .size = 64,    .slot_cnt = 64,  },
-        { .size = 80,    .slot_cnt = 51,  },
-        { .size = 96,    .slot_cnt = 42,  },
-        { .size = 112,   .slot_cnt = 36,  },
-        { .size = 128,   .slot_cnt = 64,  },
-        { .size = 160,   .slot_cnt = 51,  },
-        { .size = 192,   .slot_cnt = 64,  },
-        { .size = 224,   .slot_cnt = 54,  },
-        { .size = 10240, .slot_cnt = 6,   },
-        { .size = 20480, .slot_cnt = 1,   },
-    };
-
-    int tag_usage[max_tag + 1];
-
-    for (size_t sc_idx = 0; sc_idx < sizeof(size_classes) / sizeof(SizeClass); ++sc_idx) {
-        SizeClass &sc = size_classes[sc_idx];
-
-        const size_t full_alloc_size = sc.size;
-        const size_t alloc_size = full_alloc_size - CANARY_SIZE;
-
-        // "tdc" is short for "tag distinctness check"
-        int left_neighbor_tdc_cnt = 0;
-        int right_neighbor_tdc_cnt = 0;
-        int prev_alloc_tdc_cnt = 0;
-
-        int iter_cnt = 600;
-
-        unordered_map<uptr, u8> addr_tag_map;
-        addr_tag_map.reserve(iter_cnt * sc.slot_cnt);
-
-        u64 seen_tags = 0;
-
-        for (int iter = 0; iter < iter_cnt; ++iter) {
-            uptr allocations[256]; // 256 is max slot count
-
-            for (int i = 0; i < sc.slot_cnt; ++i) {
-                u8 *p = (u8 *) malloc(alloc_size);
-                assert(p);
-                uptr addr = (uptr) untag_pointer(p);
-                u8 tag = get_pointer_tag(p);
-
-                assert(tag >= min_tag && tag <= max_tag);
-                seen_tags |= 1 << tag;
-                ++tag_usage[tag];
-
-                // check most recent tags of left and right neighbors
-
-                auto left = addr_tag_map.find(addr - full_alloc_size);
-                if (left != addr_tag_map.end()) {
-                    assert(left->second != tag);
-                    ++left_neighbor_tdc_cnt;
-                }
-
-                auto right = addr_tag_map.find(addr + full_alloc_size);
-                if (right != addr_tag_map.end()) {
-                    assert(right->second != tag);
-                    ++right_neighbor_tdc_cnt;
-                }
-
-                // check previous tag of this slot
-                auto prev = addr_tag_map.find(addr);
-                if (prev != addr_tag_map.end()) {
-                    assert(prev->second != tag);
-                    ++prev_alloc_tdc_cnt;
-                    addr_tag_map.erase(addr);
-                }
-
-                addr_tag_map.emplace(addr, tag);
-
-                for (size_t j = 0; j < alloc_size; ++j) {
-                    // check that slot is zeroed
-                    assert(p[j] == 0);
-                    // check that slot is readable and writable
-                    p[j]++;
-                }
-
-                allocations[i] = addr;
-            }
-
-            // free some of allocations to allow their slots to be reused
-            for (int i = sc.slot_cnt - 1; i >= 0; i -= 2) {
-                free((void *) allocations[i]);
-            }
-        }
-
-        // check that all of the tags were used, except reserved ones
-        assert(seen_tags == (0xffff & ~(1 << 0 | 1 << 15)));
-
-        printf("size_class\t%i\t" "tdc_left %i\t" "tdc_right %i\t" "tdc_prev_alloc %i\n",
-               sc.size, left_neighbor_tdc_cnt, right_neighbor_tdc_cnt, prev_alloc_tdc_cnt);
-
-        // make sure tag distinctess checks were actually performed
-        int min_tdc_cnt = sc.slot_cnt * iter_cnt / 5;
-
-        assert(prev_alloc_tdc_cnt > min_tdc_cnt);
-
-        if (sc.slot_cnt > 1) {
-            assert(left_neighbor_tdc_cnt > min_tdc_cnt);
-            assert(right_neighbor_tdc_cnt > min_tdc_cnt);
-        }
-
-        // async tag check failures are reported on context switch
-        do_context_switch();
-    }
-
-    printf("\nTag use counters:\n");
-
-    int min = INT_MAX;
-    int max = 0;
-    double geomean = 0.0;
-    for (int i = min_tag; i <= max_tag; ++i) {
-        int v = tag_usage[i];
-        geomean += log(v);
-        min = std::min(min, v);
-        max = std::max(max, v);
-        printf("%i\t%i\n", i, tag_usage[i]);
-    }
-    int tag_cnt = 1 + max_tag - min_tag;
-    geomean = exp(geomean / tag_cnt);
-
-    double max_deviation = std::max((double) max - geomean, geomean - min);
-
-    printf("geomean: %.2f, max deviation from geomean: %.2f%%\n", geomean, (100.0 * max_deviation) / geomean);
-}
-
-u8* alloc_default() {
-    const size_t full_alloc_size = DEFAULT_ALLOC_SIZE + CANARY_SIZE;
-    set<uptr> addrs;
-
-    // make sure allocation has both left and right neighbors, otherwise overflow/underflow tests
-    // will fail when allocation is at the end/beginning of slab
-    for (;;) {
-        u8 *p = (u8 *) malloc(DEFAULT_ALLOC_SIZE);
-        assert(p);
-
-        uptr addr = (uptr) untag_pointer(p);
-        uptr left = addr - full_alloc_size;
-        if (addrs.find(left) != addrs.end()) {
-            uptr right = addr + full_alloc_size;
-            if (addrs.find(right) != addrs.end()) {
-                return p;
-            }
-        }
-
-        addrs.emplace(addr);
-    }
-}
-
-volatile u8 u8_var;
-
-void read_after_free() {
-    u8 *p = alloc_default();
-    free(p);
-    volatile u8 v = p[0];
-    (void) v;
-}
-
-void write_after_free() {
-    u8 *p = alloc_default();
-    free(p);
-    p[0] = 1;
-}
-
-void underflow_read() {
-    u8 *p = alloc_default();
-    volatile u8 v = p[-1];
-    (void) v;
-}
-
-void underflow_write() {
-    u8 *p = alloc_default();
-    p[-1] = 1;
-}
-
-void overflow_read() {
-    u8 *p = alloc_default();
-    volatile u8 v = p[DEFAULT_ALLOC_SIZE + CANARY_SIZE];
-    (void) v;
-}
-
-void overflow_write() {
-    u8 *p = alloc_default();
-    p[DEFAULT_ALLOC_SIZE + CANARY_SIZE] = 1;
-}
-
-void untagged_read() {
-    u8 *p = alloc_default();
-    p = (u8 *) untag_pointer(p);
-    volatile u8 v = p[0];
-    (void) v;
-}
-
-void untagged_write() {
-    u8 *p = alloc_default();
-    p = (u8 *) untag_pointer(p);
-    p[0] = 1;
-}
-
-map<string, function<void()>> tests = {
-#define TEST(s) { #s, s }
-    TEST(tag_distinctness),
-    TEST(read_after_free),
-    TEST(write_after_free),
-    TEST(overflow_read),
-    TEST(overflow_write),
-    TEST(underflow_read),
-    TEST(underflow_write),
-    TEST(untagged_read),
-    TEST(untagged_write),
-#undef TEST
-};
-
-void segv_handler(int, siginfo_t *si, void *) {
-    fprintf(stderr, "SEGV_CODE %i", si->si_code);
-    exit(139); // standard exit code for SIGSEGV
-}
-
-int main(int argc, char **argv) {
-    setbuf(stdout, NULL);
-    assert(argc == 2);
-
-    auto test_name = string(argv[1]);
-    auto test_fn = tests[test_name];
-    assert(test_fn != nullptr);
-
-    assert(mallopt(M_BIONIC_SET_HEAP_TAGGING_LEVEL, M_HEAP_TAGGING_LEVEL_ASYNC) == 1);
-
-    struct sigaction sa = {
-        .sa_sigaction = segv_handler,
-        .sa_flags = SA_SIGINFO,
-    };
-
-    assert(sigaction(SIGSEGV, &sa, nullptr) == 0);
-
-    test_fn();
-    do_context_switch();
-    
-    return 0;
-}

androidtest/src/grapheneos/hmalloc/MemtagTest.java

@@ -1,95 +0,0 @@
-package grapheneos.hmalloc;
-
-import com.android.tradefed.device.DeviceNotAvailableException;
-import com.android.tradefed.testtype.DeviceJUnit4ClassRunner;
-import com.android.tradefed.testtype.junit4.BaseHostJUnit4Test;
-
-import org.junit.Test;
-import org.junit.runner.RunWith;
-
-import java.io.IOException;
-import java.util.ArrayList;
-
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.fail;
-
-@RunWith(DeviceJUnit4ClassRunner.class)
-public class MemtagTest extends BaseHostJUnit4Test {
-
-    private static final String TEST_BINARY = "/data/local/tmp/memtag_test";
-
-    enum Result {
-        SUCCESS(0, ""),
-        // it's expected that the device is configured to use asymm MTE tag checking mode
-        ASYNC_MTE_ERROR(139, "SEGV_CODE 8"),
-        SYNC_MTE_ERROR(139, "SEGV_CODE 9"),
-        ;
-
-        public final int exitCode;
-        public final String stderr;
-
-        Result(int exitCode, String stderr) {
-            this.exitCode = exitCode;
-            this.stderr = stderr;
-        }
-    }
-
-    private static final int SEGV_EXIT_CODE = 139;
-
-    private void runTest(String name, Result expectedResult) throws DeviceNotAvailableException {
-        var args = new ArrayList<String>();
-        args.add(TEST_BINARY);
-        args.add(name);
-        String cmdLine = String.join(" ", args);
-
-        var result = getDevice().executeShellV2Command(cmdLine);
-
-        assertEquals("process exit code", expectedResult.exitCode, result.getExitCode().intValue());
-        assertEquals("stderr", expectedResult.stderr, result.getStderr());
-    }
-
-    @Test
-    public void tag_distinctness() throws DeviceNotAvailableException {
-        runTest("tag_distinctness", Result.SUCCESS);
-    }
-
-    @Test
-    public void read_after_free() throws DeviceNotAvailableException {
-        runTest("read_after_free", Result.SYNC_MTE_ERROR);
-    }
-
-    @Test
-    public void write_after_free() throws DeviceNotAvailableException {
-        runTest("write_after_free", Result.ASYNC_MTE_ERROR);
-    }
-
-    @Test
-    public void underflow_read() throws DeviceNotAvailableException {
-        runTest("underflow_read", Result.SYNC_MTE_ERROR);
-    }
-
-    @Test
-    public void underflow_write() throws DeviceNotAvailableException {
-        runTest("underflow_write", Result.ASYNC_MTE_ERROR);
-    }
-
-    @Test
-    public void overflow_read() throws DeviceNotAvailableException {
-        runTest("overflow_read", Result.SYNC_MTE_ERROR);
-    }
-
-    @Test
-    public void overflow_write() throws DeviceNotAvailableException {
-        runTest("overflow_write", Result.ASYNC_MTE_ERROR);
-    }
-
-    @Test
-    public void untagged_read() throws DeviceNotAvailableException {
-        runTest("untagged_read", Result.SYNC_MTE_ERROR);
-    }
-
-    @Test
-    public void untagged_write() throws DeviceNotAvailableException {
-        runTest("untagged_write", Result.ASYNC_MTE_ERROR);
-    }
-}

arm_mte.h

@@ -1,91 +0,0 @@
-#ifndef ARM_MTE_H
-#define ARM_MTE_H
-
-#include <arm_acle.h>
-#include <util.h>
-
-// Returns a tagged pointer.
-// See https://developer.arm.com/documentation/ddi0602/2023-09/Base-Instructions/IRG--Insert-Random-Tag-
-static inline void *arm_mte_create_random_tag(void *p, u64 exclusion_mask) {
-    return __arm_mte_create_random_tag(p, exclusion_mask);
-}
-
-// Tag the memory region with the tag specified in tag bits of tagged_ptr. Memory region itself is
-// zeroed.
-// tagged_ptr has to be aligned by 16, and len has to be a multiple of 16 (tag granule size).
-//
-// Arm's software optimization guide says:
-// "it is recommended to use STZGM (or DCZGVA) to set tag if data is not a concern." (STZGM and
-// DCGZVA are zeroing variants of tagging instructions).
-//
-// Contents of this function were copied from scudo:
-// https://android.googlesource.com/platform/external/scudo/+/refs/tags/android-14.0.0_r1/standalone/memtag.h#167
-//
-// scudo is licensed under the Apache License v2.0 with LLVM Exceptions, which is compatible with
-// the hardened_malloc's MIT license
-static inline void arm_mte_tag_and_clear_mem(void *tagged_ptr, size_t len) {
-    uintptr_t Begin = (uintptr_t) tagged_ptr;
-    uintptr_t End = Begin + len;
-    uintptr_t LineSize, Next, Tmp;
-    __asm__ __volatile__(
-        ".arch_extension memtag \n\t"
-
-        // Compute the cache line size in bytes (DCZID_EL0 stores it as the log2
-        // of the number of 4-byte words) and bail out to the slow path if DCZID_EL0
-        // indicates that the DC instructions are unavailable.
-        "DCZID .req %[Tmp] \n\t"
-        "mrs DCZID, dczid_el0 \n\t"
-        "tbnz DCZID, #4, 3f \n\t"
-        "and DCZID, DCZID, #15 \n\t"
-        "mov %[LineSize], #4 \n\t"
-        "lsl %[LineSize], %[LineSize], DCZID \n\t"
-        ".unreq DCZID \n\t"
-
-        // Our main loop doesn't handle the case where we don't need to perform any
-        // DC GZVA operations. If the size of our tagged region is less than
-        // twice the cache line size, bail out to the slow path since it's not
-        // guaranteed that we'll be able to do a DC GZVA.
-        "Size .req %[Tmp] \n\t"
-        "sub Size, %[End], %[Cur] \n\t"
-        "cmp Size, %[LineSize], lsl #1 \n\t"
-        "b.lt 3f \n\t"
-        ".unreq Size \n\t"
-
-        "LineMask .req %[Tmp] \n\t"
-        "sub LineMask, %[LineSize], #1 \n\t"
-
-        // STZG until the start of the next cache line.
-        "orr %[Next], %[Cur], LineMask \n\t"
-
-        "1:\n\t"
-        "stzg %[Cur], [%[Cur]], #16 \n\t"
-        "cmp %[Cur], %[Next] \n\t"
-        "b.lt 1b \n\t"
-
-        // DC GZVA cache lines until we have no more full cache lines.
-        "bic %[Next], %[End], LineMask \n\t"
-        ".unreq LineMask \n\t"
-
-        "2: \n\t"
-        "dc gzva, %[Cur] \n\t"
-        "add %[Cur], %[Cur], %[LineSize] \n\t"
-        "cmp %[Cur], %[Next] \n\t"
-        "b.lt 2b \n\t"
-
-        // STZG until the end of the tagged region. This loop is also used to handle
-        // slow path cases.
-
-        "3: \n\t"
-        "cmp %[Cur], %[End] \n\t"
-        "b.ge 4f \n\t"
-        "stzg %[Cur], [%[Cur]], #16 \n\t"
-        "b 3b \n\t"
-
-        "4: \n\t"
-
-        : [Cur] "+&r"(Begin), [LineSize] "=&r"(LineSize), [Next] "=&r"(Next), [Tmp] "=&r"(Tmp)
-        : [End] "r"(End)
-        : "memory"
-    );
-}
-#endif

h_malloc.c

@@ -14,7 +14,6 @@
 
 #include "h_malloc.h"
 #include "memory.h"
-#include "memtag.h"
 #include "mutex.h"
 #include "pages.h"
 #include "random.h"
@@ -76,9 +75,6 @@ static union {
         struct region_metadata *regions[2];
 #ifdef USE_PKEY
         int metadata_pkey;
-#endif
-#ifdef MEMTAG
-        bool is_memtag_disabled;
 #endif
     };
     char padding[PAGE_SIZE];
@@ -88,12 +84,6 @@ static inline void *get_slab_region_end(void) {
     return atomic_load_explicit(&ro.slab_region_end, memory_order_acquire);
 }
 
-#ifdef MEMTAG
-static inline bool is_memtag_enabled(void) {
-    return !ro.is_memtag_disabled;
-}
-#endif
-
 #define SLAB_METADATA_COUNT
 
 struct slab_metadata {
@@ -109,18 +99,6 @@ struct slab_metadata {
 #if SLAB_QUARANTINE
     u64 quarantine_bitmap[4];
 #endif
-#ifdef HAS_ARM_MTE
-    // arm_mte_tags is used as a u4 array (MTE tags are 4-bit wide)
-    //
-    // Its size is calculated by the following formula:
-    // (MAX_SLAB_SLOT_COUNT + 2) / 2
-    // MAX_SLAB_SLOT_COUNT is currently 256, 2 extra slots are needed for branchless handling of
-    // edge slots in tag_and_clear_slab_slot()
-    //
-    // It's intentionally placed at the end of struct to improve locality: for most size classes,
-    // slot count is far lower than MAX_SLAB_SLOT_COUNT.
-    u8 arm_mte_tags[129];
-#endif
 };
 
 static const size_t min_align = 16;
@@ -469,12 +447,6 @@ static void write_after_free_check(const char *p, size_t size) {
         return;
     }
 
-#ifdef HAS_ARM_MTE
-    if (likely(is_memtag_enabled())) {
-        return;
-    }
-#endif
-
     for (size_t i = 0; i < size; i += sizeof(u64)) {
         if (unlikely(*(const u64 *)(const void *)(p + i))) {
             fatal_error("detected write after free");
@@ -489,48 +461,19 @@ static void set_slab_canary_value(UNUSED struct slab_metadata *metadata, UNUSED
         0x00ffffffffffffffUL;
 
     metadata->canary_value = get_random_u64(rng) & canary_mask;
-#ifdef HAS_ARM_MTE
-    if (unlikely(metadata->canary_value == 0)) {
-        // 0 is reserved to support disabling MTE at runtime (this is required on Android).
-        // When MTE is enabled, writing and reading of canaries is disabled, i.e. canary remains zeroed.
-        // After MTE is disabled, canaries that are set to 0 are ignored, since they wouldn't match
-        // slab's metadata->canary_value.
-        // 0x100 was chosen arbitrarily, and can be encoded as an immediate value on ARM by the compiler.
-        metadata->canary_value = 0x100;
-    }
-#endif
 #endif
 }
 
 static void set_canary(UNUSED const struct slab_metadata *metadata, UNUSED void *p, UNUSED size_t size) {
 #if SLAB_CANARY
-#ifdef HAS_ARM_MTE
-    if (likely(is_memtag_enabled())) {
-        return;
-    }
-#endif
-
     memcpy((char *)p + size - canary_size, &metadata->canary_value, canary_size);
 #endif
 }
 
 static void check_canary(UNUSED const struct slab_metadata *metadata, UNUSED const void *p, UNUSED size_t size) {
 #if SLAB_CANARY
-#ifdef HAS_ARM_MTE
-    if (likely(is_memtag_enabled())) {
-        return;
-    }
-#endif
-
     u64 canary_value;
     memcpy(&canary_value, (const char *)p + size - canary_size, canary_size);
-
-#ifdef HAS_ARM_MTE
-    if (unlikely(canary_value == 0)) {
-        return;
-    }
-#endif
-
     if (unlikely(canary_value != metadata->canary_value)) {
         fatal_error("canary corrupted");
     }
@@ -563,39 +506,6 @@ static inline void stats_slab_deallocate(UNUSED struct size_class *c, UNUSED siz
 #endif
 }
 
-#ifdef HAS_ARM_MTE
-static void *tag_and_clear_slab_slot(struct slab_metadata *metadata, void *slot_ptr, size_t slot_idx, size_t slot_size) {
-    // arm_mte_tags is an array of 4-bit unsigned integers stored as u8 array (MTE tags are 4-bit wide)
-    //
-    // It stores the most recent tag for each slab slot, or 0 if the slot was never used.
-    // Slab indices in arm_mte_tags array are shifted to the right by 1, and size of this array
-    // is (MAX_SLAB_SLOT_COUNT + 2). This means that first and last values of arm_mte_tags array
-    // are always 0, which allows to handle edge slots in a branchless way when tag exclusion mask
-    // is constructed.
-    u8 *slot_tags = metadata->arm_mte_tags;
-
-    // Tag exclusion mask. 0 tag is always excluded to detect accesses to slab memory via untagged
-    // pointers. Moreover, 0 tag is excluded in bionic via PR_MTE_TAG_MASK prctl
-    u64 tem = (1 << 0) | (1 << RESERVED_TAG);
-
-    // current or previous tag of left neighbor or 0 if there's no left neighbor or if it was never used
-    tem |= (1 << u4_arr_get(slot_tags, slot_idx));
-    // previous tag of this slot or 0 if it was never used
-    tem |= (1 << u4_arr_get(slot_tags, slot_idx + 1));
-    // current or previous tag of right neighbor or 0 if there's no right neighbor or if it was never used
-    tem |= (1 << u4_arr_get(slot_tags, slot_idx + 2));
-
-    void *tagged_ptr = arm_mte_create_random_tag(slot_ptr, tem);
-    // slot addresses and sizes are always aligned by 16
-    arm_mte_tag_and_clear_mem(tagged_ptr, slot_size);
-
-    // store new tag of this slot
-    u4_arr_set(slot_tags, slot_idx + 1, get_pointer_tag(tagged_ptr));
-
-    return tagged_ptr;
-}
-#endif
-
 static inline void *allocate_small(unsigned arena, size_t requested_size) {
     struct size_info info = get_size_info(requested_size);
     size_t size = likely(info.size) ? info.size : 16;
@@ -624,11 +534,6 @@ static inline void *allocate_small(unsigned arena, size_t requested_size) {
             if (requested_size) {
                 write_after_free_check(p, size - canary_size);
                 set_canary(metadata, p, size);
-#ifdef HAS_ARM_MTE
-                if (likely(is_memtag_enabled())) {
-                    p = tag_and_clear_slab_slot(metadata, p, slot, size);
-                }
-#endif
             }
             stats_small_allocate(c, size);
 
@@ -661,11 +566,6 @@ static inline void *allocate_small(unsigned arena, size_t requested_size) {
             void *p = slot_pointer(size, slab, slot);
             if (requested_size) {
                 set_canary(metadata, p, size);
-#ifdef HAS_ARM_MTE
-                if (likely(is_memtag_enabled())) {
-                    p = tag_and_clear_slab_slot(metadata, p, slot, size);
-                }
-#endif
             }
             stats_slab_allocate(c, slab_size);
             stats_small_allocate(c, size);
@@ -688,11 +588,6 @@ static inline void *allocate_small(unsigned arena, size_t requested_size) {
         void *p = slot_pointer(size, slab, slot);
         if (requested_size) {
             set_canary(metadata, p, size);
-#ifdef HAS_ARM_MTE
-            if (likely(is_memtag_enabled())) {
-                p = tag_and_clear_slab_slot(metadata, p, slot, size);
-            }
-#endif
         }
         stats_slab_allocate(c, slab_size);
         stats_small_allocate(c, size);
@@ -717,11 +612,6 @@ static inline void *allocate_small(unsigned arena, size_t requested_size) {
     if (requested_size) {
         write_after_free_check(p, size - canary_size);
         set_canary(metadata, p, size);
-#ifdef HAS_ARM_MTE
-        if (likely(is_memtag_enabled())) {
-            p = tag_and_clear_slab_slot(metadata, p, slot, size);
-        }
-#endif
     }
     stats_small_allocate(c, size);
 
@@ -804,16 +694,7 @@ static inline void deallocate_small(void *p, const size_t *expected_size) {
     if (likely(!is_zero_size)) {
         check_canary(metadata, p, size);
 
-        bool skip_zero = false;
+        if (ZERO_ON_FREE) {
-#ifdef HAS_ARM_MTE
-        if (likely(is_memtag_enabled())) {
-            arm_mte_tag_and_clear_mem(set_pointer_tag(p, RESERVED_TAG), size);
-            // metadata->arm_mte_tags is intentionally not updated, see tag_and_clear_slab_slot()
-            skip_zero = true;
-        }
-#endif
-
-        if (ZERO_ON_FREE && !skip_zero) {
             memset(p, 0, size - canary_size);
         }
     }
@@ -1193,14 +1074,13 @@ static inline void enforce_init(void) {
     }
 }
 
-static struct mutex init_lock = MUTEX_INITIALIZER;
-
 COLD static void init_slow_path(void) {
+    static struct mutex lock = MUTEX_INITIALIZER;
 
-    mutex_lock(&init_lock);
+    mutex_lock(&lock);
 
     if (unlikely(is_init())) {
-        mutex_unlock(&init_lock);
+        mutex_unlock(&lock);
         return;
     }
 
@@ -1243,15 +1123,8 @@ COLD static void init_slow_path(void) {
     if (unlikely(memory_protect_rw_metadata(ra->regions, ra->total * sizeof(struct region_metadata)))) {
         fatal_error("failed to unprotect memory for regions table");
     }
-#ifdef HAS_ARM_MTE
+
-    if (likely(is_memtag_enabled())) {
-        ro.slab_region_start = memory_map_mte(slab_region_size);
-    } else {
     ro.slab_region_start = memory_map(slab_region_size);
-    }
-#else
-    ro.slab_region_start = memory_map(slab_region_size);
-#endif
     if (unlikely(ro.slab_region_start == NULL)) {
         fatal_error("failed to allocate slab region");
     }
@@ -1291,7 +1164,7 @@ COLD static void init_slow_path(void) {
     }
     memory_set_name(&ro, sizeof(ro), "malloc read-only after init");
 
-    mutex_unlock(&init_lock);
+    mutex_unlock(&lock);
 
     // may allocate, so wait until the allocator is initialized to avoid deadlocking
     if (unlikely(pthread_atfork(full_lock, full_unlock, post_fork_child))) {
@@ -1495,11 +1368,6 @@ EXPORT void *h_calloc(size_t nmemb, size_t size) {
     if (!ZERO_ON_FREE && likely(p != NULL) && total_size && total_size <= max_slab_size_class) {
         memset(p, 0, total_size - canary_size);
     }
-#ifdef HAS_ARM_MTE
-    // use an assert instead of adding a conditional to memset() above (freed memory is always
-    // zeroed when MTE is enabled)
-    static_assert(ZERO_ON_FREE, "disabling ZERO_ON_FREE reduces performance when ARM MTE is enabled");
-#endif
     return p;
 }
 
@@ -1517,14 +1385,11 @@ EXPORT void *h_realloc(void *old, size_t size) {
         }
     }
 
-    void *old_orig = old;
-    old = untag_pointer(old);
-
     size_t old_size;
     if (old < get_slab_region_end() && old >= ro.slab_region_start) {
         old_size = slab_usable_size(old);
         if (size <= max_slab_size_class && get_size_info(size).size == old_size) {
-            return old_orig;
+            return old;
         }
         thread_unseal_metadata();
     } else {
@@ -1637,7 +1502,7 @@ EXPORT void *h_realloc(void *old, size_t size) {
     if (copy_size > 0 && copy_size <= max_slab_size_class) {
         copy_size -= canary_size;
     }
-    memcpy(new, old_orig, copy_size);
+    memcpy(new, old, copy_size);
     if (old_size <= max_slab_size_class) {
         deallocate_small(old, NULL);
     } else {
@@ -1678,8 +1543,6 @@ EXPORT void h_free(void *p) {
         return;
     }
 
-    p = untag_pointer(p);
-
     if (p < get_slab_region_end() && p >= ro.slab_region_start) {
         thread_unseal_metadata();
         deallocate_small(p, NULL);
@@ -1703,8 +1566,6 @@ EXPORT void h_free_sized(void *p, size_t expected_size) {
         return;
     }
 
-    p = untag_pointer(p);
-
     expected_size = adjust_size_for_canary(expected_size);
 
     if (p < get_slab_region_end() && p >= ro.slab_region_start) {
@@ -1758,13 +1619,11 @@ static inline void memory_corruption_check_small(const void *p) {
     mutex_unlock(&c->lock);
 }
 
-EXPORT size_t h_malloc_usable_size(H_MALLOC_USABLE_SIZE_CONST void *arg) {
+EXPORT size_t h_malloc_usable_size(H_MALLOC_USABLE_SIZE_CONST void *p) {
-    if (arg == NULL) {
+    if (p == NULL) {
         return 0;
     }
 
-    const void *p = untag_const_pointer(arg);
-
     if (p < get_slab_region_end() && p >= ro.slab_region_start) {
         thread_unseal_metadata();
         memory_corruption_check_small(p);
@@ -2166,26 +2025,3 @@ COLD EXPORT int h_malloc_set_state(UNUSED void *state) {
     return -2;
 }
 #endif
-
-#ifdef __ANDROID__
-COLD EXPORT void h_malloc_disable_memory_tagging(void) {
-#ifdef HAS_ARM_MTE
-    mutex_lock(&init_lock);
-    if (!ro.is_memtag_disabled) {
-        if (is_init()) {
-            if (unlikely(memory_protect_rw(&ro, sizeof(ro)))) {
-                fatal_error("failed to unprotect allocator data");
-            }
-            ro.is_memtag_disabled = true;
-            if (unlikely(memory_protect_ro(&ro, sizeof(ro)))) {
-                fatal_error("failed to protect allocator data");
-            }
-        } else {
-            // bionic calls this function very early in some cases
-            ro.is_memtag_disabled = true;
-        }
-    }
-    mutex_unlock(&init_lock);
-#endif
-}
-#endif

include/h_malloc.h

@@ -99,7 +99,6 @@ int h_malloc_iterate(uintptr_t base, size_t size, void (*callback)(uintptr_t ptr
               void *arg);
 void h_malloc_disable(void);
 void h_malloc_enable(void);
-void h_malloc_disable_memory_tagging(void);
 #endif
 
 // hardened_malloc extensions

memory.c

@@ -28,20 +28,6 @@ void *memory_map(size_t size) {
     return p;
 }
 
-#ifdef HAS_ARM_MTE
-// Note that PROT_MTE can't be cleared via mprotect
-void *memory_map_mte(size_t size) {
-    void *p = mmap(NULL, size, PROT_MTE, MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
-    if (unlikely(p == MAP_FAILED)) {
-        if (errno != ENOMEM) {
-            fatal_error("non-ENOMEM MTE mmap failure");
-        }
-        return NULL;
-    }
-    return p;
-}
-#endif
-
 bool memory_map_fixed(void *ptr, size_t size) {
     void *p = mmap(ptr, size, PROT_NONE, MAP_ANONYMOUS|MAP_PRIVATE|MAP_FIXED, -1, 0);
     bool ret = p == MAP_FAILED;

memory.h

@@ -11,9 +11,6 @@
 int get_metadata_key(void);
 
 void *memory_map(size_t size);
-#ifdef HAS_ARM_MTE
-void *memory_map_mte(size_t size);
-#endif
 bool memory_map_fixed(void *ptr, size_t size);
 bool memory_unmap(void *ptr, size_t size);
 bool memory_protect_ro(void *ptr, size_t size);

memtag.h

@@ -1,49 +0,0 @@
-#ifndef MEMTAG_H
-#define MEMTAG_H
-
-#include "util.h"
-
-#ifdef HAS_ARM_MTE
-#include "arm_mte.h"
-#define MEMTAG 1
-#define RESERVED_TAG 15
-#define TAG_WIDTH 4
-#endif
-
-static inline void *untag_pointer(void *ptr) {
-#ifdef HAS_ARM_MTE
-    const uintptr_t mask = UINTPTR_MAX >> 8;
-    return (void *) ((uintptr_t) ptr & mask);
-#else
-    return ptr;
-#endif
-}
-
-static inline const void *untag_const_pointer(const void *ptr) {
-#ifdef HAS_ARM_MTE
-    const uintptr_t mask = UINTPTR_MAX >> 8;
-    return (const void *) ((uintptr_t) ptr & mask);
-#else
-    return ptr;
-#endif
-}
-
-static inline void *set_pointer_tag(void *ptr, u8 tag) {
-#ifdef HAS_ARM_MTE
-    return (void *) (((uintptr_t) tag << 56) | (uintptr_t) untag_pointer(ptr));
-#else
-    (void) tag;
-    return ptr;
-#endif
-}
-
-static inline u8 get_pointer_tag(void *ptr) {
-#ifdef HAS_ARM_MTE
-    return (((uintptr_t) ptr) >> 56) & 0xf;
-#else
-    (void) ptr;
-    return 0;
-#endif
-}
-
-#endif

util.c

@@ -6,8 +6,6 @@
 
 #ifdef __ANDROID__
 #include <async_safe/log.h>
-int mallopt(int param, int value);
-#define M_BIONIC_RESTORE_DEFAULT_SIGABRT_HANDLER (-1003)
 #endif
 
 #include "util.h"
@@ -32,7 +30,6 @@ static int write_full(int fd, const char *buf, size_t length) {
 
 COLD noreturn void fatal_error(const char *s) {
 #ifdef __ANDROID__
-    mallopt(M_BIONIC_RESTORE_DEFAULT_SIGABRT_HANDLER, 0);
     async_safe_fatal("hardened_malloc: fatal allocator error: %s", s);
 #else
     const char *prefix = "fatal allocator error: ";

util.h

@@ -57,22 +57,6 @@ static inline size_t align(size_t size, size_t align) {
     return (size + mask) & ~mask;
 }
 
-// u4_arr_{set,get} are helper functions for using u8 array as an array of unsigned 4-bit values.
-
-// val is treated as a 4-bit value
-static inline void u4_arr_set(u8 *arr, size_t idx, u8 val) {
-    size_t off = idx >> 1;
-    size_t shift = (idx & 1) << 2;
-    u8 mask = (u8) (0xf0 >> shift);
-    arr[off] = (arr[off] & mask) | (val << shift);
-}
-
-static inline u8 u4_arr_get(const u8 *arr, size_t idx) {
-    size_t off = idx >> 1;
-    size_t shift = (idx & 1) << 2;
-    return (u8) ((arr[off] >> shift) & 0xf);
-}
-
 COLD noreturn void fatal_error(const char *s);
 
 #if CONFIG_SEAL_METADATA