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

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Message-ID: <20200901142651.eir5nx4gpy63shlm@treble>
Date:   Tue, 1 Sep 2020 09:26:51 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     David Laight <David.Laight@...lab.com>
Cc:     "'x86@...nel.org'" <x86@...nel.org>,
        "'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
        'Linus Torvalds' <torvalds@...ux-foundation.org>,
        'Al Viro' <viro@...iv.linux.org.uk>,
        '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>
Subject: Re: [PATCH] x86/uaccess: Use pointer masking to limit uaccess
 speculation

On Tue, Sep 01, 2020 at 08:32:20AM +0000, David Laight wrote:
> > Yes, it would make sense to put the masking in access_ok() somehow.  But
> > to do it properly, I think we'd first need to make access_ok() generic.
> > Maybe that's do-able, but it would be a much bigger patch set.
> > 
> > First I'd prefer to just fix x86, like my patch does.  Then we could do
> > an access_ok() rework.
> 
> If you do a modified access_ok() you get to (slowly) collect all
> the important paths.
> No point replicating the same test.
> 
> A lot of the access_ok() can be deleted - maybe remove some __
> from the following functions.
> Or change to the variants that enable user-space accesses.

Well, yes, but that's a much bigger job which can be done later.

-- 
Josh