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

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Date:   Thu, 24 Feb 2022 22:31:04 -0600
From:   Dinh Nguyen <dinguyen@...nel.org>
To:     Arnd Bergmann <arnd@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>, linux-arch@...r.kernel.org,
        linux-mm@...ck.org, linux-api@...r.kernel.org, arnd@...db.de,
        linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk
Cc:     linux@...linux.org.uk, will@...nel.org, guoren@...nel.org,
        bcain@...eaurora.org, geert@...ux-m68k.org, monstr@...str.eu,
        tsbogend@...ha.franken.de, nickhu@...estech.com,
        green.hu@...il.com, shorne@...il.com, deller@....de,
        mpe@...erman.id.au, peterz@...radead.org, mingo@...hat.com,
        mark.rutland@....com, hca@...ux.ibm.com, dalias@...c.org,
        davem@...emloft.net, richard@....at, x86@...nel.org,
        jcmvbkbc@...il.com, ebiederm@...ssion.com,
        akpm@...ux-foundation.org, ardb@...nel.org,
        linux-alpha@...r.kernel.org, linux-snps-arc@...ts.infradead.org,
        linux-csky@...r.kernel.org, linux-hexagon@...r.kernel.org,
        linux-ia64@...r.kernel.org, linux-m68k@...ts.linux-m68k.org,
        linux-mips@...r.kernel.org, openrisc@...ts.librecores.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-um@...ts.infradead.org, linux-xtensa@...ux-xtensa.org
Subject: Re: [PATCH v2 13/18] uaccess: generalize access_ok()



On 2/16/22 07:13, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.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@....de>
> Acked-by: Mark Rutland <mark.rutland@....com> [arm64, asm-generic]
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>   arch/Kconfig                          |  7 ++++
>   arch/alpha/include/asm/uaccess.h      | 34 +++------------
>   arch/arc/include/asm/uaccess.h        | 29 -------------
>   arch/arm/include/asm/uaccess.h        | 20 +--------
>   arch/arm64/include/asm/uaccess.h      | 11 ++---
>   arch/csky/include/asm/uaccess.h       |  8 ----
>   arch/hexagon/include/asm/uaccess.h    | 25 ------------
>   arch/ia64/include/asm/uaccess.h       |  5 +--
>   arch/m68k/Kconfig.cpu                 |  1 +
>   arch/m68k/include/asm/uaccess.h       | 19 +--------
>   arch/microblaze/include/asm/uaccess.h |  8 +---
>   arch/mips/include/asm/uaccess.h       | 29 +------------
>   arch/nds32/include/asm/uaccess.h      |  7 +---
>   arch/nios2/include/asm/uaccess.h      | 11 +----

Acked-by: Dinh Nguyen <dinguyen@...nel.org>