Commit-ID: 4ce97317f41d38584fb93578e922fcd19e535f5b
Gitweb: https://git.kernel.org/tip/4ce97317f41d38584fb93578e922fcd19e535f5b
Author: Nick Desaulniers <ndesaulni...@google.com>
AuthorDate: Wed, 7 Aug 2019 15:15:32 -0700
Committer: Thomas Gleixner <t...@linutronix.de>
CommitDate: Thu, 8 Aug 2019 08:25:52 +0200
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 <vaibhavrust...@google.com>
Debugged-by: Vaibhav Rustagi <vaibhavrust...@google.com>
Debugged-by: Manoj Gupta <manojgu...@google.com>
Suggested-by: Alistair Delva <ade...@google.com>
Signed-off-by: Nick Desaulniers <ndesaulni...@google.com>
Signed-off-by: Thomas Gleixner <t...@linutronix.de>
Tested-by: Vaibhav Rustagi <vaibhavrust...@google.com>
Cc: sta...@vger.kernel.org
Link: https://bugs.chromium.org/p/chromium/issues/detail?id=984056
Link: https://lkml.kernel.org/r/20190807221539.94583-1-ndesaulni...@google.com
---
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(-)
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 <vgo...@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);
-}
