Hi, Thomas,
On Mon, Apr 14, 2025 at 4:29 PM Thomas Weißschuh
<[email protected]> wrote:
>
> Not all tasks have an ABI associated or 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:
>
> mips_stack_top+0x28/0xc0
> arch_pick_mmap_layout+0x190/0x220
> kunit_vm_mmap_init+0xf8/0x138
> __kunit_add_resource+0x40/0xa8
> kunit_vm_mmap+0x88/0xd8
> usercopy_test_init+0xb8/0x240
> kunit_try_run_case+0x5c/0x1a8
> kunit_generic_run_threadfn_adapter+0x28/0x50
> kthread+0x118/0x240
> ret_from_kernel_thread+0x14/0x1c
>
> Signed-off-by: Thomas Weißschuh <[email protected]>
> ---
> arch/mips/kernel/process.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
> index
> b630604c577f9ff3f2493b0f254363e499c8318c..66343cb6c1737c4217ddd8a2c3ca244fac0ef8a5
> 100644
> --- a/arch/mips/kernel/process.c
> +++ b/arch/mips/kernel/process.c
> @@ -690,9 +690,11 @@ unsigned long mips_stack_top(void)
> }
>
> /* Space for the VDSO, data page & GIC user page */
> - top -= PAGE_ALIGN(current->thread.abi->vdso->size);
> - top -= PAGE_SIZE;
> - top -= mips_gic_present() ? PAGE_SIZE : 0;
> + if (current->thread.abi) {
> + top -= PAGE_ALIGN(current->thread.abi->vdso->size);
> + top -= PAGE_SIZE;
> + top -= mips_gic_present() ? PAGE_SIZE : 0;
> + }
I think the below code should also exist only when VDSO exists.
if (current->flags & PF_RANDOMIZE)
top -= VDSO_RANDOMIZE_SIZE;
Huacai
>
> /* Space for cache colour alignment */
> if (cpu_has_dc_aliases)
>
> --
> 2.49.0
>
>
