Subject: [PATCH 6.12] tracing: Fix the bug where bpf_get_stackid returns -EFAULT on the ARM64

From: Gyokhan Kochmarla <[email-masked]>
Date: Tue, 26 May 2026 19:20:12 +0000

From: Feng Yang <[email-masked]>

commit fd2f74f8f3d3c1a524637caf5bead9757fae4332 upstream.

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/[email-masked]/
Signed-off-by: Feng Yang <[email-masked]>
Tested-by: Jiri Olsa <[email-masked]>
Acked-by: Masami Hiramatsu (Google) <[email-masked]>
Signed-off-by: Will Deacon <[email-masked]>
Signed-off-by: Gyokhan Kochmarla <[email-masked]>
---
 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 10e56522122a..46d4300dd48d 100644
--- a/arch/arm64/include/asm/ftrace.h
+++ b/arch/arm64/include/asm/ftrace.h
@@ -145,6 +145,7 @@ 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;
 }
 
-- 
2.47.3

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