| Message ID | 20190813211930.42094-1-ndesaulniers@google.com |
|---|---|
| State | New |
| Headers | show |
| Series | [4.19] x86/purgatory: Do not use __builtin_memcpy and __builtin_memset | expand |
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
On Wed, Aug 14, 2019 at 1:04 AM Greg KH <gregkh@linuxfoundation.org> wrote: > > On Tue, Aug 13, 2019 at 02:19:30PM -0700, Nick Desaulniers wrote: > > Fixes: 8fc5b4d4121c ("purgatory: core purgatory functionality") > 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. Ah yeah sorry, I should have dropped the fixes tag from the backport, as I only cared about supporting 4.19+. -- Thanks, ~Nick Desaulniers
diff --git a/arch/x86/boot/string.c b/arch/x86/boot/string.c index c4428a176973..2622c0742c92 100644 --- a/arch/x86/boot/string.c +++ b/arch/x86/boot/string.c @@ -34,6 +34,14 @@ 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; diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile index 3cf302b26332..91ef244026d2 100644 --- a/arch/x86/purgatory/Makefile +++ b/arch/x86/purgatory/Makefile @@ -6,6 +6,9 @@ purgatory-y := purgatory.o stack.o setup-x86_$(BITS).o sha256.o entry64.o string targets += $(purgatory-y) PURGATORY_OBJS = $(addprefix $(obj)/,$(purgatory-y)) +$(obj)/string.o: $(srctree)/arch/x86/boot/compressed/string.c FORCE + $(call if_changed_rule,cc_o_c) + $(obj)/sha256.o: $(srctree)/lib/sha256.c FORCE $(call if_changed_rule,cc_o_c) diff --git a/arch/x86/purgatory/purgatory.c b/arch/x86/purgatory/purgatory.c index 025c34ac0d84..7971f7a8af59 100644 --- a/arch/x86/purgatory/purgatory.c +++ b/arch/x86/purgatory/purgatory.c @@ -70,3 +70,9 @@ void purgatory(void) } copy_backup_region(); } + +/* + * Defined in order to reuse memcpy() and memset() from + * arch/x86/boot/compressed/string.c + */ +void warn(const char *msg) {} diff --git a/arch/x86/purgatory/string.c b/arch/x86/purgatory/string.c deleted file mode 100644 index 795ca4f2cb3c..000000000000 --- a/arch/x86/purgatory/string.c +++ /dev/null @@ -1,25 +0,0 @@ -/* - * Simple string functions. - * - * Copyright (C) 2014 Red Hat Inc. - * - * Author: - * Vivek Goyal <vgoyal@redhat.com> - * - * This source code is licensed under the GNU General Public License, - * Version 2. See the file COPYING for more details. - */ - -#include <linux/types.h> - -#include "../boot/string.c" - -void *memcpy(void *dst, const void *src, size_t len) -{ - return __builtin_memcpy(dst, src, len); -} - -void *memset(void *dst, int c, size_t len) -{ - return __builtin_memset(dst, c, len); -}
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. arch/x86/boot/string.c | 8 ++++++++ arch/x86/purgatory/Makefile | 3 +++ arch/x86/purgatory/purgatory.c | 6 ++++++ arch/x86/purgatory/string.c | 25 ------------------------- 4 files changed, 17 insertions(+), 25 deletions(-) delete mode 100644 arch/x86/purgatory/string.c -- 2.23.0.rc1.153.gdeed80330f-goog