linux-kernel - Re: [PATCH] x86/csum: Add KASAN/KCSAN instrumentation

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Message-ID: <CAG48ez3mfAwgkJp+GKLnbtgQoQVT78U+voRN09H5S=7Ewf+DgQ@mail.gmail.com>
Date:   Wed, 26 Jan 2022 18:47:45 +0100
From:   Jann Horn <jannh@...gle.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        kasan-dev@...glegroups.com, Eric Dumazet <edumazet@...gle.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH] x86/csum: Add KASAN/KCSAN instrumentation

On Wed, Jan 26, 2022 at 6:38 PM Dmitry Vyukov <dvyukov@...gle.com> wrote:
> On Wed, 26 Jan 2022 at 18:13, Jann Horn <jannh@...gle.com> wrote:
> >
> > In the optimized X86 version of the copy-with-checksum helpers, use
> > instrument_*() before accessing buffers from assembly code so that KASAN
> > and KCSAN don't have blind spots there.
[...]
> Can these potentially be called with KERNEL_DS as in some compat
> syscalls? If so it's better to use instrument_copy_to/from_user.
> Or probably it's better to use them anyway b/c we also want to know
> about user accesses for uaccess logging and maybe other things.

Christoph Hellwig has basically eradicated KERNEL_DS. :)

In particular, on X86, set_fs(KERNEL_DS) doesn't really do anything
anymore since commit 47058bb54b579 ("x86: remove address space
overrides using set_fs()").