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

[Thomas Weißschuh]

Hi Huacai,

On Tue, Oct 15, 2024 at 10:15:39AM +0800, Huacai Chen wrote:
> I can take this patch to the loongarch tree, but I think others should
> get upstream via kselftests tree?

Yes, sounds good.
Could you take a look at patches 2 and 4, too?

Thanks,
Thomas

> 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
> >