Re: [PATCH 2/4 v2] LoongArch: Get stack without NMI when providing regs parameter

[Huacai Chen <chenhuacai@kernel.org>]

Hi, Enze,

On Tue, Jul 25, 2023 at 2:15 PM Enze Li <lienze@kylinos.cn> wrote:
>
> Currently, arch_stack_walk() can only get the full stack information
> including NMI.  This is because the implementation of arch_stack_walk()
> is forced to ignore the information passed by the regs parameter and use
> the current stack information instead.
>
> For some detection systems like KFENCE, only partial stack information
> is needed.  In particular, the stack frame where the interrupt occurred.
>
> To support KFENCE, this patch modifies the implementation of the
> arch_stack_walk() function so that if this function is called with the
> regs argument passed, it retains all the stack information in regs and
> uses it to provide accurate information.
>
> Before the patch applied, I get,
> [    1.531195 ] ==================================================================
> [    1.531442 ] BUG: KFENCE: out-of-bounds read in stack_trace_save_regs+0x48/0x6c
> [    1.531442 ]
> [    1.531900 ] Out-of-bounds read at 0xffff800012267fff (1B left of kfence-#12):
> [    1.532046 ]  stack_trace_save_regs+0x48/0x6c
> [    1.532169 ]  kfence_report_error+0xa4/0x528
> [    1.532276 ]  kfence_handle_page_fault+0x124/0x270
> [    1.532388 ]  no_context+0x50/0x94
> [    1.532453 ]  do_page_fault+0x1a8/0x36c
> [    1.532524 ]  tlb_do_page_fault_0+0x118/0x1b4
> [    1.532623 ]  test_out_of_bounds_read+0xa0/0x1d8
> [    1.532745 ]  kunit_generic_run_threadfn_adapter+0x1c/0x28
> [    1.532854 ]  kthread+0x124/0x130
> [    1.532922 ]  ret_from_kernel_thread+0xc/0xa4
> <snip>
>
> With this patch applied, I get the correct stack information.
> [    1.320220 ] ==================================================================
> [    1.320401 ] BUG: KFENCE: out-of-bounds read in test_out_of_bounds_read+0xa8/0x1d8
> [    1.320401 ]
> [    1.320898 ] Out-of-bounds read at 0xffff800012257fff (1B left of kfence-#10):
> [    1.321134 ]  test_out_of_bounds_read+0xa8/0x1d8
> [    1.321264 ]  kunit_generic_run_threadfn_adapter+0x1c/0x28
> [    1.321392 ]  kthread+0x124/0x130
> [    1.321459 ]  ret_from_kernel_thread+0xc/0xa4
> <snip>
>
> Signed-off-by: Enze Li <lienze@kylinos.cn>
> ---
>  arch/loongarch/kernel/stacktrace.c | 20 ++++++++++++++------
>  1 file changed, 14 insertions(+), 6 deletions(-)
>
> diff --git a/arch/loongarch/kernel/stacktrace.c b/arch/loongarch/kernel/stacktrace.c
> index 2463d2fea21f..9dab30ae68ec 100644
> --- a/arch/loongarch/kernel/stacktrace.c
> +++ b/arch/loongarch/kernel/stacktrace.c
> @@ -18,16 +18,24 @@ void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
>         struct pt_regs dummyregs;
>         struct unwind_state state;
>
> -       regs = &dummyregs;
We can move the 'if (regs)' logic here and simplify the whole function.

Huacai
> -
>         if (task == current) {
> -               regs->regs[3] = (unsigned long)__builtin_frame_address(0);
> -               regs->csr_era = (unsigned long)__builtin_return_address(0);
> +               if (regs)
> +                       memcpy(&dummyregs, regs, sizeof(*regs));
> +               else {
> +                       dummyregs.regs[3] = (unsigned long)__builtin_frame_address(0);
> +                       dummyregs.csr_era = (unsigned long)__builtin_return_address(0);
> +               }
>         } else {
> -               regs->regs[3] = thread_saved_fp(task);
> -               regs->csr_era = thread_saved_ra(task);
> +               if (regs)
> +                       memcpy(&dummyregs, regs, sizeof(*regs));
> +               else {
> +                       dummyregs.regs[3] = thread_saved_fp(task);
> +                       dummyregs.csr_era = thread_saved_ra(task);
> +               }
>         }
>
> +       regs = &dummyregs;
> +
>         regs->regs[1] = 0;
>         for (unwind_start(&state, task, regs);
>              !unwind_done(&state) && !unwind_error(&state); unwind_next_frame(&state)) {
> --
> 2.34.1
>
>