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x86/purgatory: Do not use __builtin_memcpy and __builtin_memset

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commit 4ce97317f4 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 5f074f3e19 ("lib/string.c: implement a basic bcmp")

Fixes: 8fc5b4d412 ("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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Nick Desaulniers
2019-08-07 15:15:32 -07:00
committed by Greg Kroah-Hartman
parent 1182930700
commit e0d262a57f
4 changed files with 17 additions and 25 deletions
Download Patch File Download Diff File Expand all files Collapse all files

8
arch/x86/boot/string.c
View File

@@ -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;

3
arch/x86/purgatory/Makefile
View File

@@ -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)

6
arch/x86/purgatory/purgatory.c
View File

@@ -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) {}

25
arch/x86/purgatory/string.c
View File

@@ -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);
}