Re: [PATCH] tracing: Fix the bug where bpf_get_stackid returns -EFAULT on the ARM64
From: Jiri Olsa <hidden>
Date: 2025-09-25 06:50:28
Also in:
bpf, linux-arm-kernel, lkml
On Thu, Sep 25, 2025 at 10:08:22AM +0800, Feng Yang wrote:
From: Feng Yang <redacted>
When using bpf_program__attach_kprobe_multi_opts on ARM64 to hook a BPF program
that contains the bpf_get_stackid function, the BPF program fails
to obtain the stack trace and returns -EFAULT.
This is because ftrace_partial_regs omits the configuration of the pstate register,
leaving pstate at the default value of 0. When get_perf_callchain executes,
it uses user_mode(regs) to determine whether it is in kernel mode.
This leads to a misjudgment that the code is in user mode,
so perf_callchain_kernel is not executed and the function returns directly.
As a result, trace->nr becomes 0, and finally -EFAULT is returned.
Therefore, the assignment of the pstate register is added here.
Fixes: b9b55c8912ce ("tracing: Add ftrace_partial_regs() for converting ftrace_regs to pt_regs")
Closes: https://lore.kernel.org/bpf/20250919071902.554223-1-yangfeng59949@163.com/ (local)
Signed-off-by: Feng Yang <redacted>Tested-by: Jiri Olsa <jolsa@kernel.org> thanks, jirka
quoted hunk ↗ jump to hunk
--- arch/arm64/include/asm/ftrace.h | 1 + 1 file changed, 1 insertion(+)diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h index bfe3ce9df197..ba7cf7fec5e9 100644 --- a/arch/arm64/include/asm/ftrace.h +++ b/arch/arm64/include/asm/ftrace.h@@ -153,6 +153,7 @@ ftrace_partial_regs(const struct ftrace_regs *fregs, struct pt_regs *regs) regs->pc = afregs->pc; regs->regs[29] = afregs->fp; regs->regs[30] = afregs->lr; + regs->pstate = PSR_MODE_EL1h; return regs; }-- 2.25.1