Re: [PATCH] riscv: stacktrace: Fix missing the first frame

From: Conor Dooley
Date: Tue Dec 06 2022 - 11:19:00 EST


On Mon, Dec 05, 2022 at 09:29:36PM +0800, Liu Shixin wrote:
> When running kfence_test, I found some testcases failed like this:
>
> # test_out_of_bounds_read: EXPECTATION FAILED at mm/kfence/kfence_test.c:346
> Expected report_matches(&expect) to be true, but is false
> not ok 1 - test_out_of_bounds_read
>
> The corresponding call-trace is:
>
> BUG: KFENCE: out-of-bounds read in kunit_try_run_case+0x38/0x84
>
> Out-of-bounds read at 0x(____ptrval____) (32B right of kfence-#10):
> kunit_try_run_case+0x38/0x84
> kunit_generic_run_threadfn_adapter+0x12/0x1e
> kthread+0xc8/0xde
> ret_from_exception+0x0/0xc
>
> The kfence_test using the first frame of call trace to check whether the
> testcase is succeed or not. Patch a7c5c7e8ff78 skip first frame for all
> case, which results the kfence_test failed. Indeed, we only need to skip
> the first frame for case (task==NULL || task==current).
>
> With this patch, the call-trace will be:
>
> BUG: KFENCE: out-of-bounds read in test_out_of_bounds_read+0x88/0x19e
>
> Out-of-bounds read at 0x(____ptrval____) (1B left of kfence-#7):
> test_out_of_bounds_read+0x88/0x19e
> kunit_try_run_case+0x38/0x84
> kunit_generic_run_threadfn_adapter+0x12/0x1e
> kthread+0xc8/0xde
> ret_from_exception+0x0/0xc
>
> Fixes: a7c5c7e8ff78 ("riscv: eliminate unreliable __builtin_frame_address(1)")

This fixes tag is not right, did checkpatch not warn about it?

The correct fixes tag would be:
Fixes: 6a00ef449370 ("riscv: eliminate unreliable __builtin_frame_address(1)")

Maybe consider automating the creation of fixes tags, like so:
git log -1 --format='Fixes: %h (\"%s\")'

Thanks,
Conor.

> Signed-off-by: Liu Shixin <liushixin2@xxxxxxxxxx>
> ---
> arch/riscv/kernel/stacktrace.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c
> index 08d11a53f39e..5fe2ae4cf135 100644
> --- a/arch/riscv/kernel/stacktrace.c
> +++ b/arch/riscv/kernel/stacktrace.c
> @@ -30,6 +30,7 @@ void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
> fp = (unsigned long)__builtin_frame_address(0);
> sp = current_stack_pointer;
> pc = (unsigned long)walk_stackframe;
> + level = -1;
> } else {
> /* task blocked in __switch_to */
> fp = task->thread.s[0];
> @@ -41,7 +42,7 @@ void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
> unsigned long low, high;
> struct stackframe *frame;
>
> - if (unlikely(!__kernel_text_address(pc) || (level++ >= 1 && !fn(arg, pc))))
> + if (unlikely(!__kernel_text_address(pc) || (level++ >= 0 && !fn(arg, pc))))
> break;
>
> /* Validate frame pointer */
> --
> 2.25.1
>

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