[PATCH] ARM: return_address: disable again for CONFIG_ARM_UNWIND=y
From: Ard Biesheuvel <ardb@kernel.org>
Date: 2022-03-02 11:33:34
Subsystem:
arm port, function hooks (ftrace), the rest · Maintainers:
Russell King, Steven Rostedt, Masami Hiramatsu, Linus Torvalds
Commit 41918ec82eb6 ("ARM: ftrace: enable the graph tracer with the EABI
unwinder") removed the dummy version of return_address() that was
provided for the CONFIG_ARM_UNWIND=y case, on the assumption that the
removal of the kernel_text_address() call from unwind_frame() in the
preceding patch made it safe to do so.
However, this turns out not to be the case: Corentin reports warnings
about suspicious RCU usage and other strange behavior that seems to
originate in the stack unwinding that occurs in return_address().
Given that the function graph tracer (which is what these changes were
enabling for CONFIG_ARM_UNWIND=y builds) does not appear to care about
this distinction, let's revert return_address() to the old state.
Cc: Corentin Labbe <clabbe.montjoie@gmail.com>
Fixes: 41918ec82eb6 ("ARM: ftrace: enable the graph tracer with the EABI unwinder")
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/arm/include/asm/ftrace.h | 18 ++++++++++++++++++
arch/arm/kernel/Makefile | 5 ++++-
2 files changed, 22 insertions(+), 1 deletion(-)
diff --git a/arch/arm/include/asm/ftrace.h b/arch/arm/include/asm/ftrace.h
index 5358aad67831..7e9251ca29fe 100644
--- a/arch/arm/include/asm/ftrace.h
+++ b/arch/arm/include/asm/ftrace.h@@ -35,8 +35,26 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr) #ifndef __ASSEMBLY__ +#if defined(CONFIG_FRAME_POINTER) && !defined(CONFIG_ARM_UNWIND) +/* + * return_address uses walk_stackframe to do it's work. If both + * CONFIG_FRAME_POINTER=y and CONFIG_ARM_UNWIND=y walk_stackframe uses unwind + * information. For this to work in the function tracer many functions would + * have to be marked with __notrace. So for now just depend on + * !CONFIG_ARM_UNWIND. + */ + void *return_address(unsigned int); +#else + +static inline void *return_address(unsigned int level) +{ + return NULL; +} + +#endif + #define ftrace_return_address(n) return_address(n) #define ARCH_HAS_SYSCALL_MATCH_SYM_NAME
diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index 5cebb8d5a1d6..56511856ff9d 100644
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile@@ -25,7 +25,10 @@ obj-y := elf.o entry-common.o irq.o opcodes.o \ KASAN_SANITIZE_stacktrace.o := n KASAN_SANITIZE_traps.o := n -obj-y += return_address.o +ifneq ($(CONFIG_ARM_UNWIND),y) +obj-$(CONFIG_FRAME_POINTER) += return_address.o +endif + obj-$(CONFIG_ATAGS) += atags_parse.o obj-$(CONFIG_ATAGS_PROC) += atags_proc.o obj-$(CONFIG_DEPRECATED_PARAM_STRUCT) += atags_compat.o
--
2.30.2
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