From 4ce97317f41d38584fb93578e922fcd19e535f5b Mon Sep 17 00:00:00 2001 From: Nick Desaulniers Date: Wed, 7 Aug 2019 15:15:32 -0700 Subject: x86/purgatory: Do not use __builtin_memcpy and __builtin_memset Implementing memcpy and memset in terms of __builtin_memcpy and __builtin_memset is problematic. GCC at -O2 will replace calls to the builtins with calls to memcpy and memset (but will generate an inline implementation at -Os). Clang will replace the builtins with these calls regardless of optimization level. $ llvm-objdump -dr arch/x86/purgatory/string.o | tail 0000000000000339 memcpy: 339: 48 b8 00 00 00 00 00 00 00 00 movabsq $0, %rax 000000000000033b: R_X86_64_64 memcpy 343: ff e0 jmpq *%rax 0000000000000345 memset: 345: 48 b8 00 00 00 00 00 00 00 00 movabsq $0, %rax 0000000000000347: R_X86_64_64 memset 34f: ff e0 Such code results in infinite recursion at runtime. This is observed when doing kexec. Instead, reuse an implementation from arch/x86/boot/compressed/string.c. This requires to implement a stub function for warn(). Also, Clang may lower memcmp's that compare against 0 to bcmp's, so add a small definition, too. See also: commit 5f074f3e192f ("lib/string.c: implement a basic bcmp") Fixes: 8fc5b4d4121c ("purgatory: core purgatory functionality") Reported-by: Vaibhav Rustagi Debugged-by: Vaibhav Rustagi Debugged-by: Manoj Gupta Suggested-by: Alistair Delva Signed-off-by: Nick Desaulniers Signed-off-by: Thomas Gleixner Tested-by: Vaibhav Rustagi Cc: stable@vger.kernel.org Link: https://bugs.chromium.org/p/chromium/issues/detail?id=984056 Link: https://lkml.kernel.org/r/20190807221539.94583-1-ndesaulniers@google.com --- arch/x86/boot/string.c | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'arch/x86/boot') diff --git a/arch/x86/boot/string.c b/arch/x86/boot/string.c index 401e30ca0a75..8272a4492844 100644 --- a/arch/x86/boot/string.c +++ b/arch/x86/boot/string.c @@ -37,6 +37,14 @@ int memcmp(const void *s1, const void *s2, size_t len) return diff; } +/* + * Clang may lower `memcmp == 0` to `bcmp == 0`. + */ +int bcmp(const void *s1, const void *s2, size_t len) +{ + return memcmp(s1, s2, len); +} + int strcmp(const char *str1, const char *str2) { const unsigned char *s1 = (const unsigned char *)str1; -- cgit v1.2.3