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@xxxxxxxxxx>
Debugged-by: Vaibhav Rustagi <vaibhavrustagi@xxxxxxxxxx>
Debugged-by: Manoj Gupta <manojgupta@xxxxxxxxxx>
Suggested-by: Alistair Delva <adelva@xxxxxxxxxx>
Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Vaibhav Rustagi <vaibhavrustagi@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://bugs.chromium.org/p/chromium/issues/detail?id=984056
Link: https://lkml.kernel.org/r/20190807221539.94583-1-ndesaulniers@xxxxxxxxxx
---
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
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@xxxxxxxxxx>
- *
- * 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);
-}
--
2.23.0.rc1.153.gdeed80330f-goog
