Re: [PATCH] riscv: fix out of bounds in walk_stackframe

[Alexandre Ghiti]

Hi Edward,

On Fri, Sep 29, 2023 at 1:12 AM Edward AD <twuufnxlz@xxxxxxxxx> wrote:
>
> Add vmalloc and kernel addresses check to prevent invalid access.
>
> Closes: https://lore.kernel.org/all/20230926105949.1025995-2-twuufnxlz@xxxxxxxxx/
> Fixes: 5d8544e2d007 ("RISC-V: Generic library routines and assembly")
> Reported-and-test-by: syzbot+8d2757d62d403b2d9275@xxxxxxxxxxxxxxxxxxxxxxxxx
> Link: https://lore.kernel.org/all/0000000000000170df0605ccf91a@xxxxxxxxxx/T/
> Signed-off-by: Edward AD <twuufnxlz@xxxxxxxxx>
> ---
>  arch/riscv/kernel/stacktrace.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c
> index 64a9c093aef9..031a4a35c1d0 100644
> --- a/arch/riscv/kernel/stacktrace.c
> +++ b/arch/riscv/kernel/stacktrace.c
> @@ -54,6 +54,9 @@ void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
>                         break;
>                 /* Unwind stack frame */
>                 frame = (struct stackframe *)fp - 1;
> +               if ((is_vmalloc_addr(frame) && !pfn_valid(page_to_pfn(vmalloc_to_page(frame)))) ||
> +                    !virt_addr_valid(frame))
> +                       break;
>                 sp = fp;
>                 if (regs && (regs->epc == pc) && (frame->fp & 0x7)) {
>                         fp = frame->ra;
> --
> 2.25.1
>

I'm still not convinced this will fix the kasan out-of-bounds
accesses, the page can be valid but the read can happen at an offset
not initialized and trigger such errors right? I still think there is
something weird about the stack frame, as to me this should not happen
(but admittedly I don't know much about that).