On Mon, 14 Oct 2024 at 19:36, 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>
> ---
Thanks very much for fixing this: the usercopy tests and kunit_vm_mmap
stuff has been broken on quite a few architectures, so I really
appreciate this being fixed "day one" for KUnit support. :-)
We'll take the rest of the patches via the kunit/kselftest tree; I
agree that it makes more sense for this one to go in separately via
loongarch.
Thanks,
-- David
> 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
>
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