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ARM: 9184/1: return_address: disable again for CONFIG_ARM_UNWIND=y

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Commit 41918ec82e ("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: 41918ec82e ("ARM: ftrace: enable the graph tracer with the EABI unwinder")
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reported-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Tested-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
This commit is contained in:
Ard Biesheuvel 2022-03-02 12:38:18 +01:00 • committed by Russell King (Oracle)
parent 8167937647
commit 6845d64d51
2 changed files with 22 additions and 1 deletions
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18
arch/arm/include/asm/ftrace.h
View file

@ -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

5
arch/arm/kernel/Makefile
View file

@ -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