Re: [PATCH v5] riscv: stacktrace: fix stack-out-of-bounds in walk_stackframe()

[Nam Cao <namcao@linutronix.de>]

Jiakai Xu <xujiakai2025@iscas.ac.cn> writes:

> The fp_is_valid() function uses ALIGN(sp, THREAD_SIZE) as the upper
> bound for the frame pointer check. This bound is calculated relative
> to the current sp and shifts upward when sp itself exceeds the valid
> stack region, allowing the unwinder to read past the end of the
> allocated task stack and triggering KASAN stack-out-of-bounds.
>
> Fix this by using absolute stack boundaries determined once before
> the unwind loop:
>
> - When sp is on the task stack, use the task's pt_regs as the upper
>   bound.
> - When sp is on the overflow_stack (CONFIG_VMAP_STACK=y), use the
>   overflow_stack's top as the boundary.
> - When sp is on the IRQ stack (CONFIG_IRQ_STACKS=y), use the IRQ
>   stack's top as the boundary.
> - When sp is not on any known stack, warn and return.
> - For remote tasks (task != current), if sp is not on the task
>   stack, warn and return since we cannot reliably determine the
>   correct boundary from a different CPU's stacks.
>
> Make the DECLARE_PER_CPU(overflow_stack) unconditional in
> asm/stacktrace.h so that stacktrace.c can use
> IS_ENABLED(CONFIG_VMAP_STACK) instead of #ifdef, in line with the
> kernel coding style which discourages the use of #ifdef in .c files
> (https://docs.kernel.org/process/coding-style.html).  This is safe
> because the DEFINE_PER_CPU (memory allocation) in traps.c remains
> guarded by CONFIG_VMAP_STACK; the reference in stacktrace.c is only
> compiled when IS_ENABLED(CONFIG_VMAP_STACK) evaluates to true.
>
> Fixes: a2a4d4a6a0bf ("riscv: stacktrace: fixed walk_stackframe()")
> Signed-off-by: Jiakai Xu <xujiakai2025@iscas.ac.cn>
> Assisted-by: YuanSheng:DeepSeek-V3.2

Reviewed-by: Nam Cao <namcao@linutronix.de>