Re: [PATCH v7 03/10] riscv: ftrace: use the frame pointer as the function graph return-address cookie

[sashiko-bot@kernel.org]

> The function graph tracer stamps every shadow-stack entry with a
> cookie, ftrace_ret_stack::retp, which stack unwinders later pass to
> ftrace_graph_ret_addr() to recover a return address that the tracer
> replaced with return_to_handler.  The match is an exact pointer
> comparison, so the producer and the consumer must agree on what the
> cookie is.  On riscv they don't:
> 
>   * The dynamic ftrace path stores &arch_ftrace_regs(fregs)->ra, a
>     slot inside the transient ftrace trampoline frame.  The frame is
>     popped as soon as the callback returns, so the stored cookie is
>     an address that no consumer can ever reproduce.  It has never
>     matched anything since ftrace_graph_func() was introduced in
>     v6.8.
> 
>   * The frame-pointer walker in walk_stackframe() passes &frame->ra,
> [ ... ]
> 
> Fixes: 35e61e8827ee8 ("riscv: ftrace: Make function graph use ftrace directly")
> Suggested-by: Martin Kaiser <martin@kaiser.cx>
> Cc: stable@vger.kernel.org
> Signed-off-by: Shuai Xue <xueshuai@linux.alibaba.com>

Sashiko has reviewed this patch and found no issues.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261110013750.36800-1-xueshuai@linux.alibaba.com?part=3