Re: [PATCH v7 04/10] riscv: stacktrace: Add frame record metadata

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Medium] riscv: entry: use call instead of tail for handle_bad_stack()
--

commit ed05329452fecde9e16a00910af1efec91f2922b
Author: Wang Han <wanghan@linux.alibaba.com>

riscv: stacktrace: Add frame record metadata

This commit adds a metadata frame record to struct pt_regs and initializes
it across exception, overflow, boot, and task-creation entry boundaries
for frame-pointer stack unwinding.

> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> index 61b7a77166971..4c69132d59785 100644
> --- a/arch/riscv/kernel/entry.S
> +++ b/arch/riscv/kernel/entry.S

[ ... ]

> @@ -354,6 +376,19 @@ SYM_CODE_START_LOCAL(handle_kernel_stack_overflow)
>  	REG_S s3, PT_BADADDR(sp)
>  	REG_S s4, PT_CAUSE(sp)
>  	REG_S s5, PT_TP(sp)
> +
> +	/*
> +	 * Create a metadata frame record for the overflow pt_regs. The
> +	 * overflow path is entered from kernel context, so this is a nested
> +	 * pt_regs boundary and the unwinder can resume from the pre-overflow
> +	 * frame pointer saved in PT_S0.
> +	 */
> +	REG_S zero, (S_STACKFRAME + FRAME_RECORD_FP)(sp)
> +	REG_S zero, (S_STACKFRAME + FRAME_RECORD_RA)(sp)
> +	li t0, FRAME_META_TYPE_PT_REGS
> +	REG_S t0, S_STACKFRAME_TYPE(sp)
> +	addi s0, sp, S_STACKFRAME + STACKFRAME_RECORD_SIZE
> +
>  	move a0, sp
>  	tail handle_bad_stack
>  SYM_CODE_END(handle_kernel_stack_overflow)

[Severity: Medium]
Should this use "call handle_bad_stack" instead of "tail handle_bad_stack"?

Because tail does not update ra, handle_bad_stack()'s prologue saves a
frame record on the overflow stack that pairs the new s0 (pointing at the
overflow pt_regs metadata record) with the interrupted pre-overflow ra.
When panic() unwinds from handle_bad_stack(), the unwinder consumes
regs->ra before reaching the pt_regs metadata record, and if that return
address was hooked by function_graph or kretprobes, recovering it with the
overflow-stack fp fails and aborts the stack trace before reaching the
overflowed task stack.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261110013750.36800-1-xueshuai@linux.alibaba.com?part=4