linux-kernel - Re: [PATCH] x86/uaccess: Fix 32-bit __get_user_asm_u64() when CC_HAS_ASM_GOTO

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Message-ID: <CAHk-=whF01ZS30vQAEjY9K4RM_QNjZ0mTCTt8SY4KuER-2d14w@mail.gmail.com>
Date:   Mon, 13 Sep 2021 10:05:32 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Will Deacon <will@...nel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Bill Wendling <morbo@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] x86/uaccess: Fix 32-bit __get_user_asm_u64() when CC_HAS_ASM_GOTO_OUTPUT=y

On Mon, Sep 13, 2021 at 9:36 AM Will Deacon <will@...nel.org> wrote:
>
> Use the existing '__gu_ptr' source pointer to unsigned int for 32-bit
> __get_user_asm_u64() instead of the original pointer.

Heh. And by "existing" you mean "the one that exists _purely_ for this
exact reason and that wasn't used" ;)

What a silly bug. And it's existed for a year, which I think shows
just how little 32-bit x86 is used these days (*).

            Linus

(*) but also probably how few 64-bit user accesses we do - the fact
that the bug was actually found by the "copy_from_kernel_nofault" code
that just shares the infrastructure on x86 rather than any user access
code is kind of interesting.