linux-kernel - Re: [PATCH 00/25] objtool: UACCESS validation v4

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Message-ID: <20190318235707.wdaldl2354fxmbab@treble>
Date:   Mon, 18 Mar 2019 18:57:07 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     torvalds@...ux-foundation.org, tglx@...utronix.de, hpa@...or.com,
        julien.thierry@....com, will.deacon@....com, luto@...capital.net,
        mingo@...nel.org, catalin.marinas@....com, james.morse@....com,
        valentin.schneider@....com, brgerst@...il.com, luto@...nel.org,
        bp@...en8.de, dvlasenk@...hat.com, linux-kernel@...r.kernel.org,
        dvyukov@...gle.com, rostedt@...dmis.org
Subject: Re: [PATCH 00/25] objtool: UACCESS validation v4

On Mon, Mar 18, 2019 at 04:38:40PM +0100, Peter Zijlstra wrote:
> Teach objtool to validate the UACCESS (SMAP, PAN) rules which are currently
> unenforced and (therefore obviously) violated.
> 
> UACCESS sections should be small; we want to limit the amount of code that can
> touch userspace. Furthermore, UACCESS state isn't scheduled, this means that
> anything that directly calls into the scheduler will result in random code
> running with UACCESS enabled and possibly getting back into the UACCESS region
> with UACCESS disabled and causing faults.
> 
> Forbid any CALL/RET while UACCESS is enabled; but provide a few exceptions.
> 
> This builds x86_64-allmodconfig and lots of x86_64-randconfig clean.
> 
> Changes since -v3:
> 
>  - removed a bunch of functions from the UACCESS-safe list
>    due to the removal of CONFIG_KASAN_EXTRA=y.
> 
>  - hopefully addressed all the feedback from Josh
> 
>  - realized objtool doesn't cover x86_32
> 
>  - some added additional annotations/fixes: kcov, signal
> 
>  - retains the DF check for now, Linus, do you (still) think it is worth doing
>    that DF check?

I'm still not crazy about the DF thing, but otherwise everything looks
great.

For the objtool bits:

Acked-by: Josh Poimboeuf <jpoimboe@...hat.com>

-- 
Josh