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https://github.com/Divested-Mobile/DivestOS-Build.git
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215 lines
8.4 KiB
Diff
215 lines
8.4 KiB
Diff
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From a9803a869bfc274d57ab33862ad7a5ea31df4559 Mon Sep 17 00:00:00 2001
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From: Cesar Eduardo Barros <cesarb@cesarb.eti.br>
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Date: Mon, 25 Nov 2013 22:00:41 -0200
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Subject: [PATCH] crypto: more robust crypto_memneq
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Disabling compiler optimizations can be fragile, since a new
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optimization could be added to -O0 or -Os that breaks the assumptions
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the code is making.
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Instead of disabling compiler optimizations, use a dummy inline assembly
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(based on RELOC_HIDE) to block the problematic kinds of optimization,
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while still allowing other optimizations to be applied to the code.
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The dummy inline assembly is added after every OR, and has the
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accumulator variable as its input and output. The compiler is forced to
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assume that the dummy inline assembly could both depend on the
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accumulator variable and change the accumulator variable, so it is
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forced to compute the value correctly before the inline assembly, and
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cannot assume anything about its value after the inline assembly.
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This change should be enough to make crypto_memneq work correctly (with
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data-independent timing) even if it is inlined at its call sites. That
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can be done later in a followup patch.
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Compile-tested on x86_64.
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Change-Id: Ib82641bedec576d2be3793db4d8da36a4ccbbe75
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Signed-off-by: Cesar Eduardo Barros <cesarb@cesarb.eti.br>
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Acked-by: Daniel Borkmann <dborkman@redhat.com>
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Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
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---
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crypto/Makefile | 5 ---
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crypto/memneq.c | 79 +++++++++++++++++++++++++++++-------------
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include/linux/compiler-gcc.h | 3 ++
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include/linux/compiler-intel.h | 7 ++++
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include/linux/compiler.h | 4 +++
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5 files changed, 68 insertions(+), 30 deletions(-)
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diff --git a/crypto/Makefile b/crypto/Makefile
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index ae3684d16f3..4c75316f7d6 100644
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--- a/crypto/Makefile
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+++ b/crypto/Makefile
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@@ -2,11 +2,6 @@
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# Cryptographic API
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#
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-# memneq MUST be built with -Os or -O0 to prevent early-return optimizations
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-# that will defeat memneq's actual purpose to prevent timing attacks.
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-CFLAGS_REMOVE_memneq.o := -O1 -O2 -O3
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-CFLAGS_memneq.o := -Os
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-
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obj-$(CONFIG_CRYPTO) += crypto.o
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crypto-y := api.o cipher.o compress.o memneq.o
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diff --git a/crypto/memneq.c b/crypto/memneq.c
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index 40dfa50d39b..a285a744bc7 100644
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--- a/crypto/memneq.c
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+++ b/crypto/memneq.c
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@@ -73,6 +73,7 @@ __crypto_memneq_generic(const void *a, const void *b, size_t size)
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#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
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while (size >= sizeof(unsigned long)) {
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neq |= *(unsigned long *)a ^ *(unsigned long *)b;
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+ OPTIMIZER_HIDE_VAR(neq);
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a += sizeof(unsigned long);
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b += sizeof(unsigned long);
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size -= sizeof(unsigned long);
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@@ -80,6 +81,7 @@ __crypto_memneq_generic(const void *a, const void *b, size_t size)
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#endif /* CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS */
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while (size > 0) {
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neq |= *(unsigned char *)a ^ *(unsigned char *)b;
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+ OPTIMIZER_HIDE_VAR(neq);
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a += 1;
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b += 1;
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size -= 1;
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@@ -90,33 +92,60 @@ __crypto_memneq_generic(const void *a, const void *b, size_t size)
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/* Loop-free fast-path for frequently used 16-byte size */
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static inline unsigned long __crypto_memneq_16(const void *a, const void *b)
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{
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+ unsigned long neq = 0;
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+
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#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
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- if (sizeof(unsigned long) == 8)
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- return ((*(unsigned long *)(a) ^ *(unsigned long *)(b))
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- | (*(unsigned long *)(a+8) ^ *(unsigned long *)(b+8)));
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- else if (sizeof(unsigned int) == 4)
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- return ((*(unsigned int *)(a) ^ *(unsigned int *)(b))
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- | (*(unsigned int *)(a+4) ^ *(unsigned int *)(b+4))
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- | (*(unsigned int *)(a+8) ^ *(unsigned int *)(b+8))
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- | (*(unsigned int *)(a+12) ^ *(unsigned int *)(b+12)));
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- else
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+ if (sizeof(unsigned long) == 8) {
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+ neq |= *(unsigned long *)(a) ^ *(unsigned long *)(b);
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+ OPTIMIZER_HIDE_VAR(neq);
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+ neq |= *(unsigned long *)(a+8) ^ *(unsigned long *)(b+8);
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+ OPTIMIZER_HIDE_VAR(neq);
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+ } else if (sizeof(unsigned int) == 4) {
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+ neq |= *(unsigned int *)(a) ^ *(unsigned int *)(b);
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+ OPTIMIZER_HIDE_VAR(neq);
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+ neq |= *(unsigned int *)(a+4) ^ *(unsigned int *)(b+4);
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+ OPTIMIZER_HIDE_VAR(neq);
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+ neq |= *(unsigned int *)(a+8) ^ *(unsigned int *)(b+8);
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+ OPTIMIZER_HIDE_VAR(neq);
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+ neq |= *(unsigned int *)(a+12) ^ *(unsigned int *)(b+12);
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+ OPTIMIZER_HIDE_VAR(neq);
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+ } else {
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#endif /* CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS */
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- return ((*(unsigned char *)(a) ^ *(unsigned char *)(b))
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- | (*(unsigned char *)(a+1) ^ *(unsigned char *)(b+1))
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- | (*(unsigned char *)(a+2) ^ *(unsigned char *)(b+2))
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- | (*(unsigned char *)(a+3) ^ *(unsigned char *)(b+3))
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- | (*(unsigned char *)(a+4) ^ *(unsigned char *)(b+4))
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- | (*(unsigned char *)(a+5) ^ *(unsigned char *)(b+5))
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- | (*(unsigned char *)(a+6) ^ *(unsigned char *)(b+6))
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- | (*(unsigned char *)(a+7) ^ *(unsigned char *)(b+7))
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- | (*(unsigned char *)(a+8) ^ *(unsigned char *)(b+8))
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- | (*(unsigned char *)(a+9) ^ *(unsigned char *)(b+9))
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- | (*(unsigned char *)(a+10) ^ *(unsigned char *)(b+10))
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- | (*(unsigned char *)(a+11) ^ *(unsigned char *)(b+11))
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- | (*(unsigned char *)(a+12) ^ *(unsigned char *)(b+12))
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- | (*(unsigned char *)(a+13) ^ *(unsigned char *)(b+13))
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- | (*(unsigned char *)(a+14) ^ *(unsigned char *)(b+14))
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- | (*(unsigned char *)(a+15) ^ *(unsigned char *)(b+15)));
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+ neq |= *(unsigned char *)(a) ^ *(unsigned char *)(b);
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+ OPTIMIZER_HIDE_VAR(neq);
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+ neq |= *(unsigned char *)(a+1) ^ *(unsigned char *)(b+1);
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+ OPTIMIZER_HIDE_VAR(neq);
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+ neq |= *(unsigned char *)(a+2) ^ *(unsigned char *)(b+2);
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+ OPTIMIZER_HIDE_VAR(neq);
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+ neq |= *(unsigned char *)(a+3) ^ *(unsigned char *)(b+3);
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+ OPTIMIZER_HIDE_VAR(neq);
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+ neq |= *(unsigned char *)(a+4) ^ *(unsigned char *)(b+4);
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+ OPTIMIZER_HIDE_VAR(neq);
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+ neq |= *(unsigned char *)(a+5) ^ *(unsigned char *)(b+5);
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+ OPTIMIZER_HIDE_VAR(neq);
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+ neq |= *(unsigned char *)(a+6) ^ *(unsigned char *)(b+6);
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+ OPTIMIZER_HIDE_VAR(neq);
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+ neq |= *(unsigned char *)(a+7) ^ *(unsigned char *)(b+7);
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+ OPTIMIZER_HIDE_VAR(neq);
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+ neq |= *(unsigned char *)(a+8) ^ *(unsigned char *)(b+8);
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+ OPTIMIZER_HIDE_VAR(neq);
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+ neq |= *(unsigned char *)(a+9) ^ *(unsigned char *)(b+9);
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+ OPTIMIZER_HIDE_VAR(neq);
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+ neq |= *(unsigned char *)(a+10) ^ *(unsigned char *)(b+10);
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+ OPTIMIZER_HIDE_VAR(neq);
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+ neq |= *(unsigned char *)(a+11) ^ *(unsigned char *)(b+11);
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+ OPTIMIZER_HIDE_VAR(neq);
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+ neq |= *(unsigned char *)(a+12) ^ *(unsigned char *)(b+12);
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+ OPTIMIZER_HIDE_VAR(neq);
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+ neq |= *(unsigned char *)(a+13) ^ *(unsigned char *)(b+13);
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+ OPTIMIZER_HIDE_VAR(neq);
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+ neq |= *(unsigned char *)(a+14) ^ *(unsigned char *)(b+14);
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+ OPTIMIZER_HIDE_VAR(neq);
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+ neq |= *(unsigned char *)(a+15) ^ *(unsigned char *)(b+15);
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+ OPTIMIZER_HIDE_VAR(neq);
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+ }
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+
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+ return neq;
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}
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/* Compare two areas of memory without leaking timing information,
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diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
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index e5834aa24b9..8c999ad4545 100644
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--- a/include/linux/compiler-gcc.h
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+++ b/include/linux/compiler-gcc.h
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@@ -34,6 +34,9 @@
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__asm__ ("" : "=r"(__ptr) : "0"(ptr)); \
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(typeof(ptr)) (__ptr + (off)); })
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+/* Make the optimizer believe the variable can be manipulated arbitrarily. */
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+#define OPTIMIZER_HIDE_VAR(var) __asm__ ("" : "=r" (var) : "0" (var))
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+
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#ifdef __CHECKER__
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#define __must_be_array(arr) 0
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#else
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diff --git a/include/linux/compiler-intel.h b/include/linux/compiler-intel.h
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index d8e636e5607..966fa6820d9 100644
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--- a/include/linux/compiler-intel.h
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+++ b/include/linux/compiler-intel.h
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@@ -15,6 +15,7 @@
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*/
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#undef barrier
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#undef RELOC_HIDE
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+#undef OPTIMIZER_HIDE_VAR
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#define barrier() __memory_barrier()
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@@ -23,6 +24,12 @@
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__ptr = (unsigned long) (ptr); \
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(typeof(ptr)) (__ptr + (off)); })
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+/* This should act as an optimization barrier on var.
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+ * Given that this compiler does not have inline assembly, a compiler barrier
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+ * is the best we can do.
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+ */
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+#define OPTIMIZER_HIDE_VAR(var) barrier()
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+
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/* Intel ECC compiler doesn't support __builtin_types_compatible_p() */
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#define __must_be_array(a) 0
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diff --git a/include/linux/compiler.h b/include/linux/compiler.h
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index 923d093c9ce..a8ef3ca7af2 100644
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--- a/include/linux/compiler.h
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+++ b/include/linux/compiler.h
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@@ -164,6 +164,10 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
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(typeof(ptr)) (__ptr + (off)); })
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#endif
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+#ifndef OPTIMIZER_HIDE_VAR
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+#define OPTIMIZER_HIDE_VAR(var) barrier()
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+#endif
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+
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#endif /* __KERNEL__ */
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#endif /* __ASSEMBLY__ */
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