linux-kernel - Re: [PATCH 3/8] powerpc: Mark functions called inside uaccess blocks w/ 'notrace'

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Message-ID: <20201016094132.GI2611@hirez.programming.kicks-ass.net>
Date:   Fri, 16 Oct 2020 11:41:32 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     "Christopher M. Riedl" <cmr@...efail.de>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/8] powerpc: Mark functions called inside uaccess blocks
 w/ 'notrace'

On Fri, Oct 16, 2020 at 07:56:16AM +0100, Christoph Hellwig wrote:
> On Thu, Oct 15, 2020 at 10:01:54AM -0500, Christopher M. Riedl wrote:
> > Functions called between user_*_access_begin() and user_*_access_end()
> > should be either inlined or marked 'notrace' to prevent leaving
> > userspace access exposed. Mark any such functions relevant to signal
> > handling so that subsequent patches can call them inside uaccess blocks.
> 
> I don't think running this much code with uaccess enabled is a good
> idea.  Please refactor the code to reduce the criticial sections with
> uaccess enabled.
> 
> Btw, does powerpc already have the objtool validation that we don't
> accidentally jump out of unsafe uaccess critical sections?

It does not, there was some effort on that a while ago, but I suspect
they're waiting for the ARM64 effort to land and build on that.