linux-kernel - Re: [PATCH 5/6] objtool: Add UACCESS validation

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Message-ID: <20190227173046.GU32494@hirez.programming.kicks-ass.net>
Date:   Wed, 27 Feb 2019 18:30:46 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>, Peter Anvin <hpa@...or.com>,
        Julien Thierry <julien.thierry@....com>,
        Will Deacon <will.deacon@....com>,
        Andy Lutomirski <luto@...capital.net>,
        Ingo Molnar <mingo@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        James Morse <james.morse@....com>, valentin.schneider@....com,
        Brian Gerst <brgerst@...il.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andrew Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH 5/6] objtool: Add UACCESS validation

On Wed, Feb 27, 2019 at 08:18:21AM -0800, Linus Torvalds wrote:

> So the whole "run with AC on" thing isn't a big deal, apart from the
> scheduling case.
> 
> And we know how to fix the scheduling case by just doing the
> save/restore thing..

Right, but I was hoping to avoid having to do that; and I think we can
do that if we push all of kasan_report into an exception, like that
'patch' I just posted.

If I'm not mistaken the regular kasan house-keeping crud just prods at
the shadow memory with simple code and should be perfectly safe.