Re: [PATCH] ARM: kretprobes: fix out-of-range literal issue in naked asm routine
From: Masami Hiramatsu <mhiramat@kernel.org>
Date: 2022-03-25 09:43:31
On Fri, 25 Mar 2022 09:03:02 +0100 Ard Biesheuvel [off-list ref] wrote:
__kretprobe_trampoline is a naked C function implemented in asm, and the first thing it does is take its own address and record it in the frame record, so that a backtrace will properly traverse its stackframe. As it turns out, using 'LDR <reg>, =<symbol>' notation is problematic here, as it relies on a literal pool to be emitted sufficiently close to the LDR instruction, and since the compiler is not aware of this need, this results in assembler errors in some cases. Since the address taken is guaranteed to be the address of the instruction itself, just use ADR instead.
Ah, indeed :) This looks good to me. Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org> Tested-by: Masami Hiramatsu <mhiramat@kernel.org> Thank you very much!
quoted hunk ↗ jump to hunk
Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Nick Desaulniers <ndesaulniers@google.com> Reported-by: kernel test robot <redacted> Fixes: 7e9bf33b8124 ("ARM: kprobes: Make a frame pointer on __kretprobe_trampoline") Signed-off-by: Ard Biesheuvel <ardb@kernel.org> --- arch/arm/probes/kprobes/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)diff --git a/arch/arm/probes/kprobes/core.c b/arch/arm/probes/kprobes/core.c index 9090c3a74dcc..068639a777c8 100644 --- a/arch/arm/probes/kprobes/core.c +++ b/arch/arm/probes/kprobes/core.c@@ -377,7 +377,7 @@ void __naked __kprobes __kretprobe_trampoline(void) { __asm__ __volatile__ ( #ifdef CONFIG_FRAME_POINTER - "ldr lr, =__kretprobe_trampoline \n\t" + "adr lr, . \n\t" /* __kretprobe_trampoline makes a framepointer on pt_regs. */ #ifdef CONFIG_CC_IS_CLANG "stmdb sp, {sp, lr, pc} \n\t"-- 2.30.2
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