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 if we define warn as a symbol. 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")

Cc: stable@vger.kernel.org Fixes: 8fc5b4d4121c ("purgatory: core purgatory functionality") Link: https://bugs.chromium.org/p/chromium/issues/detail?id=984056 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 Tested-by: Vaibhav Rustagi vaibhavrustagi@google.com --- Changes v4 -> v5: * None Changes v3 -> v4: * (style) open brace on newline * drop Vaibhav's SOB tag that was accidentally copy+pasta'd from v1. * Carry Vaibhav's tested by tag from v3 since v4 is strictly stylistic change from v3. * Drop cc'ing stable. Sasha's bot reports v1 doesn't cherry pick cleanly 5.1, so this series will require manual backports. Changes v2 -> v3: * Add bcmp implementation. * Drop tested-by tag (Vaibhav will help retest). * Cc stable Changes v1 -> v2: * Add Fixes tag. * Move this patch to first in the series.

arch/x86/boot/string.c | 8 ++++++++ arch/x86/purgatory/Makefile | 3 +++ arch/x86/purgatory/purgatory.c | 6 ++++++ arch/x86/purgatory/string.c | 23 ----------------------- 4 files changed, 17 insertions(+), 23 deletions(-) delete mode 100644 arch/x86/purgatory/string.c

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; 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 6d8d5a34c377..b607bda786f6 100644 --- a/arch/x86/purgatory/purgatory.c +++ b/arch/x86/purgatory/purgatory.c @@ -68,3 +68,9 @@ 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 01ad43873ad9..000000000000 --- a/arch/x86/purgatory/string.c +++ /dev/null @@ -1,23 +0,0 @@ -// SPDX-License-Identifier: GPL-2.0-only -/* - * Simple string functions. - * - * Copyright (C) 2014 Red Hat Inc. - * - * Author: - * Vivek Goyal vgoyal@redhat.com - */ - -#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); -}