linux-kernel - Re: [PATCH v2 13/18] uaccess: generalize access

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Date:   Thu, 17 Feb 2022 08:52:29 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linux API <linux-api@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>
Cc:     Russell King - ARM Linux <linux@...linux.org.uk>,
        Will Deacon <will@...nel.org>, Guo Ren <guoren@...nel.org>,
        Brian Cain <bcain@...eaurora.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Michal Simek <monstr@...str.eu>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Nick Hu <nickhu@...estech.com>,
        Greentime Hu <green.hu@...il.com>,
        Dinh Nguyen <dinguyen@...nel.org>,
        Stafford Horne <shorne@...il.com>,
        Helge Deller <deller@....de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Rich Felker <dalias@...c.org>,
        David Miller <davem@...emloft.net>,
        Richard Weinberger <richard@....at>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Max Filippov <jcmvbkbc@...il.com>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        alpha <linux-alpha@...r.kernel.org>,
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        "open list:QUALCOMM HEXAGON..." <linux-hexagon@...r.kernel.org>,
        linux-ia64@...r.kernel.org,
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        <linux-xtensa@...ux-xtensa.org>
Subject: Re: [PATCH v2 13/18] uaccess: generalize access_ok()

On Wed, Feb 16, 2022 at 2:13 PM Arnd Bergmann <arnd@...nel.org> wrote:

> + * limit and catch all possible overflows.
> + * On architectures with separate user address space (m68k, s390, parisc,
> + * sparc64) or those without an MMU, this should always return true.
...
> +static inline int __access_ok(const void __user *ptr, unsigned long size)
> +{
> +       unsigned long limit = user_addr_max();
> +       unsigned long addr = (unsigned long)ptr;
> +
> +       if (IS_ENABLED(CONFIG_ALTERNATE_USER_ADDRESS_SPACE))
> +               return true;

I noticed that I'm missing the check for !CONFIG_MMU here, despite
mentioning that in the comment above it. I've added it now.

        Arnd