linux-kernel - [PATCH] tracing: Fix the bug where bpf_get

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Message-Id: <20250925020822.119302-1-yangfeng59949@163.com>
Date: Thu, 25 Sep 2025 10:08:22 +0800
From: Feng Yang <yangfeng59949@....com>
To: rostedt@...dmis.org,
	mhiramat@...nel.org,
	mark.rutland@....com,
	catalin.marinas@....com,
	will@...nel.org,
	revest@...omium.org,
	alexei.starovoitov@...il.com,
	olsajiri@...il.com,
	andrii@...nel.org,
	ast@...nel.org
Cc: linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	bpf@...r.kernel.org
Subject: [PATCH] tracing: Fix the bug where bpf_get_stackid returns -EFAULT on the ARM64

From: Feng Yang <yangfeng@...inos.cn>

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/
Signed-off-by: Feng Yang <yangfeng@...inos.cn>
---
 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