linux-kernel - Re: [PATCH mm] fix for "kasan, fork: reset pointer tags of vmapped stacks"

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Date:   Wed, 16 Feb 2022 10:59:06 +0100
From:   Marco Elver <elver@...gle.com>
To:     andrey.konovalov@...ux.dev
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: [PATCH mm] fix for "kasan, fork: reset pointer tags of vmapped stacks"

On Tue, 15 Feb 2022 at 17:52, <andrey.konovalov@...ux.dev> wrote:
>
> From: Andrey Konovalov <andreyknvl@...gle.com>
>
> That patch didn't update the case when a stack is retrived from
> cached_stacks in alloc_thread_stack_node(). As cached_stacks stores
> vm_structs and not stack pointers themselves, the pointer tag needs
> to be reset there as well.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>

Reviewed-by: Marco Elver <elver@...gle.com>

Did the test catch this? If not, can this be tested?

> ---
>  kernel/fork.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 57d624f05182..5e3ad2e7a756 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -226,15 +226,17 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
>                 if (!s)
>                         continue;
>
> -               /* Mark stack accessible for KASAN. */
> +               /* Reset stack metadata. */
>                 kasan_unpoison_range(s->addr, THREAD_SIZE);
>
> +               stack = kasan_reset_tag(s->addr);
> +
>                 /* Clear stale pointers from reused stack. */
> -               memset(s->addr, 0, THREAD_SIZE);
> +               memset(stack, 0, THREAD_SIZE);
>
>                 tsk->stack_vm_area = s;
> -               tsk->stack = s->addr;
> -               return s->addr;
> +               tsk->stack = stack;
> +               return stack;
>         }
>
>         /*
> --
> 2.25.1
>