linux-kernel - Re: [PATCH] fork, vmalloc: KASAN-poison backing pages of vmapped stacks

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Date:   Mon, 23 Jan 2023 17:45:55 +0100
From:   Andrey Konovalov <andreyknvl@...il.com>
To:     Jann Horn <jannh@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Uladzislau Rezki <urezki@...il.com>,
        Christoph Hellwig <hch@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        linux-kernel@...r.kernel.org,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        kasan-dev@...glegroups.com
Subject: Re: [PATCH] fork, vmalloc: KASAN-poison backing pages of vmapped stacks

On Tue, Jan 17, 2023 at 5:35 PM Jann Horn <jannh@...gle.com> wrote:
>
> KASAN (except in HW_TAGS mode) tracks memory state based on virtual
> addresses. The mappings of kernel stack pages in the linear mapping are
> currently marked as fully accessible.
> Since stack corruption issues can cause some very gnarly errors, let's be
> extra careful and tell KASAN to forbid accesses to stack memory through the
> linear mapping.
>
> Signed-off-by: Jann Horn <jannh@...gle.com>
> ---
> I wrote this after seeing
> https://lore.kernel.org/all/Y8W5rjKdZ9erIF14@casper.infradead.org/
> and wondering about possible ways that this kind of stack corruption
> could be sneaking past KASAN.
> That's proooobably not the explanation, but still...

Hi Jann,

if you decide to keep KASAN poisoning after addressing Dmitry's
comments, please add a KASAN KUnit test for this.

Thank you!