linux-kernel - Re: [PATCH 5/6] [v2] asm-generic: uaccess: remove inline strncpy_from_user/strnlen

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Date:   Mon, 17 May 2021 09:27:01 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Christoph Hellwig <hch@....de>
Cc:     linux-arch <linux-arch@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Vineet Gupta <vgupta@...opsys.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Brian Cain <bcain@...eaurora.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Jeff Dike <jdike@...toit.com>,
        Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Sid Manning <sidneym@...eaurora.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...nel.org>,
        "open list:SYNOPSYS ARC ARCHITECTURE" 
        <linux-snps-arc@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
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        <uclinux-h8-devel@...ts.sourceforge.jp>,
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        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        linux-um <linux-um@...ts.infradead.org>
Subject: Re: [PATCH 5/6] [v2] asm-generic: uaccess: remove inline strncpy_from_user/strnlen_user

On Mon, May 17, 2021 at 8:20 AM Christoph Hellwig <hch@....de> wrote:
>
> On Sat, May 15, 2021 at 12:18:02PM +0200, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@...db.de>
> >
> > Consolidate the asm-generic implementation with the library version
> > that is used everywhere else.
> >
> > These are the three versions for NOMMU kernels,
>
> I don't get the three versions part?

Right, that was confusing. Rewording to

| The inline version is used on three NOMMU architectures and is
| particularly inefficient when it scans the string one byte at a time
| twice. It also lacks a check for user_addr_max(), but this is
| probably ok on NOMMU targets.
|
| Consolidate the asm-generic implementation with the library version
| that is used everywhere else.  This version is generalized enough to
| work efficiently on both MMU and NOMMU targets, and using the
| same code everywhere reduces the potential for subtle bugs.

> > +     select GENERIC_STRNCPY_FROM_USER
> > +     select GENERIC_STRNLEN_USER
>
> Given that most architetures select the generic version I wonder
> if it might be worth to add another patch to invert the logic so
> that architectures with their own implementation need to sekect a symbol.

Done now, using 'CONFIG_ARCH_HAS_{STRNCPY_FROM,STRNLEN}_USER'.

There are still seven or eight architectures that provide their own though.

> > +extern long strncpy_from_user(char *dst, const char __user *src, long count);
> > +extern long strnlen_user(const char __user *src, long n);
>
> No need for the extern here.

Removed.

       Arnd