linux-kernel - Re: [PATCH v3] x86/uaccess: Use pointer masking to limit uaccess speculation

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Message-ID: <20200914175604.GF680@zn.tnic>
Date:   Mon, 14 Sep 2020 19:56:04 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     x86@...nel.org, Al Viro <viro@...iv.linux.org.uk>,
        linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Will Deacon <will@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Waiman Long <longman@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Andy Lutomirski <luto@...nel.org>,
        Christoph Hellwig <hch@....de>,
        David Laight <David.Laight@...lab.com>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v3] x86/uaccess: Use pointer masking to limit uaccess
 speculation

On Thu, Sep 10, 2020 at 12:22:53PM -0500, Josh Poimboeuf wrote:
> +/*
> + * Sanitize a user pointer such that it becomes NULL if it's not a valid user
> + * pointer.  This prevents speculative dereferences of user-controlled pointers
> + * to kernel space when access_ok() speculatively returns true.  This should be
> + * done *after* access_ok(), to avoid affecting error handling behavior.

Err, stupid question: can this macro then be folded into access_ok() so
that you don't have to touch so many places and the check can happen
automatically?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette