* [PATCH v5 1/2] x86/purgatory: do not use __builtin_memcpy and __builtin_memset
@ 2019-08-07 22:15 Nick Desaulniers
2019-08-07 22:15 ` [PATCH v5 2/2] x86/purgatory: use CFLAGS_REMOVE rather than reset KBUILD_CFLAGS Nick Desaulniers
0 siblings, 1 reply; 2+ messages in thread
From: Nick Desaulniers @ 2019-08-07 22:15 UTC (permalink / raw)
To: tglx, mingo, bp
Cc: peterz, clang-built-linux, linux-kernel, yamada.masahiro,
Nick Desaulniers, stable, Vaibhav Rustagi, Manoj Gupta,
Alistair Delva, H. Peter Anvin, x86, Allison Randal,
Enrico Weigelt, Chao Fan, Greg Kroah-Hartman, Alexios Zavras
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);
-}
--
2.22.0.770.g0f2c4a37fd-goog
^ permalink raw reply related [flat|nested] 2+ messages in thread
* [PATCH v5 2/2] x86/purgatory: use CFLAGS_REMOVE rather than reset KBUILD_CFLAGS
2019-08-07 22:15 [PATCH v5 1/2] x86/purgatory: do not use __builtin_memcpy and __builtin_memset Nick Desaulniers
@ 2019-08-07 22:15 ` Nick Desaulniers
0 siblings, 0 replies; 2+ messages in thread
From: Nick Desaulniers @ 2019-08-07 22:15 UTC (permalink / raw)
To: tglx, mingo, bp
Cc: peterz, clang-built-linux, linux-kernel, yamada.masahiro,
Nick Desaulniers, stable, Vaibhav Rustagi, H. Peter Anvin, x86
KBUILD_CFLAGS is very carefully built up in the top level Makefile,
particularly when cross compiling or using different build tools.
Resetting KBUILD_CFLAGS via := assignment is an antipattern.
The comment above the reset mentions that -pg is problematic. Other
Makefiles use `CFLAGS_REMOVE_file.o = $(CC_FLAGS_FTRACE)` when
CONFIG_FUNCTION_TRACER is set. Prefer that pattern to wiping out all of
the important KBUILD_CFLAGS then manually having to re-add them. Seems
also that __stack_chk_fail references are generated when using
CONFIG_STACKPROTECTOR or CONFIG_STACKPROTECTOR_STRONG.
Cc: stable@vger.kernel.org
Fixes: 8fc5b4d4121c ("purgatory: core purgatory functionality")
Reported-by: Vaibhav Rustagi <vaibhavrustagi@google.com>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Vaibhav Rustagi <vaibhavrustagi@google.com>
---
Changes v4 -> v5:
* Add RETPOLINE_CFLAGS when CONFIG_RETPOLINE=y as per tglx.
* Add tglx's Suggested-by tag.
Changes v3 -> v4:
* Use tabs to align flags (stylistic change only).
* Drop stable tag, patch 01/02 doesn't apply earlier than 5.1.
* Add tglx's suggested by tag for the tabs.
* Carry Vaibhav's tested by tag from v3 since v4 is simply stylistic.
Changes v2 -> v3:
* Prefer $(CC_FLAGS_FTRACE) which is exported to -pg.
* Also check CONFIG_STACKPROTECTOR and CONFIG_STACKPROTECTOR_STRONG.
* Cc stable.
Changes v1 -> v2:
Rather than manually add -mno-sse, -mno-mmx, -mno-sse2, prefer to filter
-pg flags.
arch/x86/purgatory/Makefile | 26 +++++++++++++++++++++-----
1 file changed, 21 insertions(+), 5 deletions(-)
arch/x86/purgatory/Makefile | 33 ++++++++++++++++++++++++++++-----
1 file changed, 28 insertions(+), 5 deletions(-)
diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
index 91ef244026d2..8901a1f89cf5 100644
--- a/arch/x86/purgatory/Makefile
+++ b/arch/x86/purgatory/Makefile
@@ -20,11 +20,34 @@ KCOV_INSTRUMENT := n
# Default KBUILD_CFLAGS can have -pg option set when FTRACE is enabled. That
# in turn leaves some undefined symbols like __fentry__ in purgatory and not
-# sure how to relocate those. Like kexec-tools, use custom flags.
-
-KBUILD_CFLAGS := -fno-strict-aliasing -Wall -Wstrict-prototypes -fno-zero-initialized-in-bss -fno-builtin -ffreestanding -c -Os -mcmodel=large
-KBUILD_CFLAGS += -m$(BITS)
-KBUILD_CFLAGS += $(call cc-option,-fno-PIE)
+# sure how to relocate those.
+ifdef CONFIG_FUNCTION_TRACER
+CFLAGS_REMOVE_sha256.o += $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_purgatory.o += $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_string.o += $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_kexec-purgatory.o += $(CC_FLAGS_FTRACE)
+endif
+
+ifdef CONFIG_STACKPROTECTOR
+CFLAGS_REMOVE_sha256.o += -fstack-protector
+CFLAGS_REMOVE_purgatory.o += -fstack-protector
+CFLAGS_REMOVE_string.o += -fstack-protector
+CFLAGS_REMOVE_kexec-purgatory.o += -fstack-protector
+endif
+
+ifdef CONFIG_STACKPROTECTOR_STRONG
+CFLAGS_REMOVE_sha256.o += -fstack-protector-strong
+CFLAGS_REMOVE_purgatory.o += -fstack-protector-strong
+CFLAGS_REMOVE_string.o += -fstack-protector-strong
+CFLAGS_REMOVE_kexec-purgatory.o += -fstack-protector-strong
+endif
+
+ifdef CONFIG_RETPOLINE
+CFLAGS_REMOVE_sha256.o += $(RETPOLINE_CFLAGS)
+CFLAGS_REMOVE_purgatory.o += $(RETPOLINE_CFLAGS)
+CFLAGS_REMOVE_string.o += $(RETPOLINE_CFLAGS)
+CFLAGS_REMOVE_kexec-purgatory.o += $(RETPOLINE_CFLAGS)
+endif
$(obj)/purgatory.ro: $(PURGATORY_OBJS) FORCE
$(call if_changed,ld)
--
2.22.0.770.g0f2c4a37fd-goog
^ permalink raw reply related [flat|nested] 2+ messages in thread
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