From mboxrd@z Thu Jan  1 00:00:00 1970
From: Geert Uytterhoeven <geert@linux-m68k.org>
Subject: Re: [PATCH v2 13/18] uaccess: generalize access_ok()
Date: Fri, 18 Feb 2022 10:04:48 +0100
Message-ID: <CAMuHMdVfiuYEMQhtscwt4xCm1Dfw0M_qEmQ4pof59eB4jZFOPg@mail.gmail.com>
References: <20220216131332.1489939-1-arnd@kernel.org> <20220216131332.1489939-14-arnd@kernel.org>
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To: Arnd Bergmann <arnd@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>, Christoph Hellwig <hch@lst.de>, Linux-Arch <linux-arch@vger.kernel.org>, Linux MM <linux-mm@kvack.org>, Linux API <linux-api@vger.kernel.org>, Arnd Bergmann <arnd@arndb.de>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Al Viro <viro@zeniv.linux.org.uk>, Russell King <linux@armlinux.org.uk>, Will Deacon <will@kernel.org>, Guo Ren <guoren@kernel.org>, Brian Cain <bcain@codeaurora.org>, Michal Simek <monstr@monstr.eu>, Thomas Bogendoerfer <tsbogend@alpha.franken.de>, Nick Hu <nickhu@andestech.com>, Greentime Hu <green.hu@gmail.com>, Dinh Nguyen <dinguyen@kernel.org>, Stafford Horne <shorne@gmail.com>, Helge Deller <deller@gmx.de>, Michael Ellerman <mpe@ellerman.id.au>, Peter

On Wed, Feb 16, 2022 at 2:17 PM Arnd Bergmann <arnd@kernel.org> wrote:
> From: Arnd Bergmann <arnd@arndb.de>
>
> There are many different ways that access_ok() is defined across
> architectures, but in the end, they all just compare against the
> user_addr_max() value or they accept anything.
>
> Provide one definition that works for most architectures, checking
> against TASK_SIZE_MAX for user processes or skipping the check inside
> of uaccess_kernel() sections.
>
> For architectures without CONFIG_SET_FS(), this should be the fastest
> check, as it comes down to a single comparison of a pointer against a
> compile-time constant, while the architecture specific versions tend to
> do something more complex for historic reasons or get something wrong.
>
> Type checking for __user annotations is handled inconsistently across
> architectures, but this is easily simplified as well by using an inline
> function that takes a 'const void __user *' argument. A handful of
> callers need an extra __user annotation for this.
>
> Some architectures had trick to use 33-bit or 65-bit arithmetic on the
> addresses to calculate the overflow, however this simpler version uses
> fewer registers, which means it can produce better object code in the
> end despite needing a second (statically predicted) branch.
>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Acked-by: Mark Rutland <mark.rutland@arm.com> [arm64, asm-generic]
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

>  arch/m68k/Kconfig.cpu                 |  1 +
>  arch/m68k/include/asm/uaccess.h       | 19 +--------

Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds