Re: [PATCH 1/4] LoongArch: Don't crash in stack_top() for tasks without vDSO

[Huacai Chen]

Hi, Thomas,

I can take this patch to the loongarch tree, but I think others should
get upstream via kselftests tree?

Huacai

On Mon, Oct 14, 2024 at 7:36 PM Thomas Weißschuh
<thomas.weissschuh@xxxxxxxxxxxxx> wrote:
>
> Not all tasks have a vDSO mapped, for example kthreads never do.
> If such a task ever ends up calling stack_top(), it will derefence the
> NULL vdso pointer and crash.
>
> This can for example happen when using kunit:
>
>         [<9000000000203874>] stack_top+0x58/0xa8
>         [<90000000002956cc>] arch_pick_mmap_layout+0x164/0x220
>         [<90000000003c284c>] kunit_vm_mmap_init+0x108/0x12c
>         [<90000000003c1fbc>] __kunit_add_resource+0x38/0x8c
>         [<90000000003c2704>] kunit_vm_mmap+0x88/0xc8
>         [<9000000000410b14>] usercopy_test_init+0xbc/0x25c
>         [<90000000003c1db4>] kunit_try_run_case+0x5c/0x184
>         [<90000000003c3d54>] kunit_generic_run_threadfn_adapter+0x24/0x48
>         [<900000000022e4bc>] kthread+0xc8/0xd4
>         [<9000000000200ce8>] ret_from_kernel_thread+0xc/0xa4
>
> Fixes: 803b0fc5c3f2 ("LoongArch: Add process management")
> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@xxxxxxxxxxxxx>
> ---
>  arch/loongarch/kernel/process.c | 16 +++++++++-------
>  1 file changed, 9 insertions(+), 7 deletions(-)
>
> diff --git a/arch/loongarch/kernel/process.c b/arch/loongarch/kernel/process.c
> index f2ff8b5d591e4fd638109d2c98d75543c01a112c..6e58f65455c7ca3eae2e88ed852c8655a6701e5c 100644
> --- a/arch/loongarch/kernel/process.c
> +++ b/arch/loongarch/kernel/process.c
> @@ -293,13 +293,15 @@ unsigned long stack_top(void)
>  {
>         unsigned long top = TASK_SIZE & PAGE_MASK;
>
> -       /* Space for the VDSO & data page */
> -       top -= PAGE_ALIGN(current->thread.vdso->size);
> -       top -= VVAR_SIZE;
> -
> -       /* Space to randomize the VDSO base */
> -       if (current->flags & PF_RANDOMIZE)
> -               top -= VDSO_RANDOMIZE_SIZE;
> +       if (current->thread.vdso) {
> +               /* Space for the VDSO & data page */
> +               top -= PAGE_ALIGN(current->thread.vdso->size);
> +               top -= VVAR_SIZE;
> +
> +               /* Space to randomize the VDSO base */
> +               if (current->flags & PF_RANDOMIZE)
> +                       top -= VDSO_RANDOMIZE_SIZE;
> +       }
>
>         return top;
>  }
>
> --
> 2.47.0
>