Hi, Thomas,
On Tue, Apr 15, 2025 at 3:10 PM Thomas Weißschuh
<thomas.weisssc...@linutronix.de> 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 ABI 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
>
> Only dereference the ABI point if it is set.
>
> Also move the randomization adjustment into the same conditional.
>
> Signed-off-by: Thomas Weißschuh <thomas.weisssc...@linutronix.de>
> ---
> arch/mips/kernel/process.c | 16 +++++++++-------
> 1 file changed, 9 insertions(+), 7 deletions(-)
>
> diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
> index
> b630604c577f9ff3f2493b0f254363e499c8318c..02aa6a04a21da437909eeac4f149155cc298f5b5
> 100644
> --- a/arch/mips/kernel/process.c
> +++ b/arch/mips/kernel/process.c
> @@ -690,18 +690,20 @@ 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'm not sure, but maybe this line has nothing to do with VDSO.
Huacai
> +
> + /* Space to randomize the VDSO base */
> + if (current->flags & PF_RANDOMIZE)
> + top -= VDSO_RANDOMIZE_SIZE;
> + }
>
> /* Space for cache colour alignment */
> if (cpu_has_dc_aliases)
> top -= shm_align_mask + 1;
>
> - /* Space to randomize the VDSO base */
> - if (current->flags & PF_RANDOMIZE)
> - top -= VDSO_RANDOMIZE_SIZE;
> -
> return top;
> }
>
>
> --
> 2.49.0
>
