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

[Huacai Chen]

On Tue, Oct 15, 2024 at 2:14 PM Thomas Weißschuh
<thomas.weissschuh@xxxxxxxxxxxxx> wrote:
>
> 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?

Bibo is more familiar with those, so +CC Bibo.
This one is queued in the loongarch tree. Thanks.

Huacai

>
> 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
> > >