linux-kernel - Re: objtool clac/stac handling change..

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Message-ID: <20200702140447.GN2786714@ZenIV.linux.org.uk>
Date:   Thu, 2 Jul 2020 15:04:47 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Christophe Leroy <christophe.leroy@....fr>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: objtool clac/stac handling change..

On Thu, Jul 02, 2020 at 03:01:59PM +0100, Al Viro wrote:
> On Thu, Jul 02, 2020 at 11:34:31PM +1000, Michael Ellerman wrote:
> 
> > I think we can do something to make it work.
> > 
> > We don't have an equivalent of x86's ex_handler_uaccess(), so it's not
> > quite as easy as whacking a user_access_end() in there.
> > 
> > Probably the simplest option for us is to just handle it in our
> > unsafe_op_wrap(). I'll try and come up with something tomorrow.
> 
> The goal is to avoid using unsafe_op_wrap()...

Incidentally, the change Linus proposes would affect unsafe_put_user()
as well.  And you are not using unsafe_op_wrap() anywhere on that
path...