On Tue, Aug 13, 2019 at 02:19:30PM -0700, Nick Desaulniers wrote:
commit 4ce97317f41d38584fb93578e922fcd19e535f5b upstream.
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 vaibhavrustagi@google.com Debugged-by: Vaibhav Rustagi vaibhavrustagi@google.com Debugged-by: Manoj Gupta manojgupta@google.com Suggested-by: Alistair Delva adelva@google.com Signed-off-by: Nick Desaulniers ndesaulniers@google.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Tested-by: Vaibhav Rustagi vaibhavrustagi@google.com 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
This failed to cherry-pick back cleanly due to the SPDX license identifier not existing in arch/x86/purgatory/string.c in 4.19. `git rm` it anyway.
Now queued up, thanks.
So the Fixes: tag does not mean this should be backported to anything older? It implies this bug has been in the kernel since the 3.17 release.
thanks,
greg k-h