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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 2 Apr 2020 12:26:52 -0700
Message-ID: <CAHk-=wg9cSm=AjPmkasNHBDwuW4D10jszjv6EeCKp8V9Qbx2hg@mail.gmail.com>
Subject: Re: [PATCH RESEND 1/4] uaccess: Add user_read_access_begin/end and user_write_access_begin/end
To:     Kees Cook <keescook@chromium.org>
Cc:     Al Viro <viro@zeniv.linux.org.uk>,
        Christophe Leroy <christophe.leroy@c-s.fr>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Dave Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Andrew Morton <akpm@linux-foundation.org>,
        Peter Anvin <hpa@zytor.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
        Linux-MM <linux-mm@kvack.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Russell King <linux@armlinux.org.uk>,
        Christian Borntraeger <borntraeger@de.ibm.com>
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On Thu, Apr 2, 2020 at 11:36 AM Kees Cook <keescook@chromium.org> wrote:
>
> Yup, I think it's a weakness of the ARM implementation and I'd like to
> not extend it further. AFAIK we should never nest, but I would not be
> surprised at all if we did.

Wel, at least the user_access_begin/end() sections can't nest. objtool
verifies and warns about that on x86.

> If we were looking at a design goal for all architectures, I'd like
> to be doing what the public PaX patchset

We already do better than PaX ever did. Seriously. Mainline has long
since passed their hacky garbage.

Plus PaX  and grsecurity should be actively shunned. Don't look at it,
don't use it, and tell everybody you know to not use that shit.

                Linus