From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 From: anupritaisno1 Date: Wed, 13 Oct 2021 15:00:25 +0530 Subject: [PATCH] add a real explicit_bzero implementation Clang, GCC and other compilers special-case standard C functions like memset. Calls to memset will be optimized out. OpenBSD provides explicit_bzero to work around this but Android simply defines it as memset so nothing prevents it from being optimized away. This implementation uses a memory read constraint via empty inline assembly rather than something that may be broken via link-time optimization in the future. Signed-off-by: anupritaisno1 Change-Id: Ia021e30f86ee4b998d541fbf7262110f9d1d6fbf Signed-off-by: anupritaisno1 --- libc/Android.bp | 1 + libc/bionic/explicit_bzero.cpp | 7 +++++++ libc/include/string.h | 1 + libc/libc.map.txt | 1 + libc/upstream-openbsd/android/include/openbsd-compat.h | 2 -- 5 files changed, 10 insertions(+), 2 deletions(-) create mode 100644 libc/bionic/explicit_bzero.cpp diff --git a/libc/Android.bp b/libc/Android.bp index 75b06f58c..cae5d8776 100644 --- a/libc/Android.bp +++ b/libc/Android.bp @@ -1084,6 +1084,7 @@ cc_library_static { "bionic/error.cpp", "bionic/eventfd.cpp", "bionic/exec.cpp", + "bionic/explicit_bzero.cpp", "bionic/faccessat.cpp", "bionic/fchmod.cpp", "bionic/fchmodat.cpp", diff --git a/libc/bionic/explicit_bzero.cpp b/libc/bionic/explicit_bzero.cpp new file mode 100644 index 000000000..b06daa138 --- /dev/null +++ b/libc/bionic/explicit_bzero.cpp @@ -0,0 +1,7 @@ +#include + +void* explicit_bzero(void* s, size_t n) { + void *ptr = memset(s, 0, n); + __asm__ __volatile__("" : : "r"(ptr) : "memory"); + return ptr; +} diff --git a/libc/include/string.h b/libc/include/string.h index 0cc5611aa..befffd082 100644 --- a/libc/include/string.h +++ b/libc/include/string.h @@ -56,6 +56,7 @@ void* mempcpy(void* __dst, const void* __src, size_t __n) __INTRODUCED_IN(23); #endif void* memmove(void* __dst, const void* __src, size_t __n); void* memset(void* __dst, int __ch, size_t __n); +void* explicit_bzero(void *s, size_t n); void* memmem(const void* __haystack, size_t __haystack_size, const void* __needle, size_t __needle_size) __attribute_pure__; char* strchr(const char* __s, int __ch) __attribute_pure__; diff --git a/libc/libc.map.txt b/libc/libc.map.txt index c31e30681..cab7c1363 100644 --- a/libc/libc.map.txt +++ b/libc/libc.map.txt @@ -332,6 +332,7 @@ LIBC { execvp; execvpe; # introduced=21 exit; + explicit_bzero; # introduced=31 faccessat; fallocate; # introduced=21 fallocate64; # introduced=21 diff --git a/libc/upstream-openbsd/android/include/openbsd-compat.h b/libc/upstream-openbsd/android/include/openbsd-compat.h index 6c21c5b49..49d98c3d2 100644 --- a/libc/upstream-openbsd/android/include/openbsd-compat.h +++ b/libc/upstream-openbsd/android/include/openbsd-compat.h @@ -57,8 +57,6 @@ extern const char* __progname; /* OpenBSD has this, but we can't really implement it correctly on Linux. */ #define issetugid() 0 -#define explicit_bzero(p, s) memset(p, 0, s) - /* OpenBSD has this in paths.h. But this directory doesn't normally exist. * Even when it does exist, only the 'shell' user has permissions. */