linux-kernel - Re: [PATCH PTI v3 03/10] x86/pti/64: Fix ESPFIX64 user mapping

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Message-ID: <20171214141038.7bddwvkabuy6ikxm@node.shutemov.name>
Date:   Thu, 14 Dec 2017 17:10:38 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     X86 ML <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        David Laight <David.Laight@...lab.com>,
        Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH PTI v3 03/10] x86/pti/64: Fix ESPFIX64 user mapping

On Wed, Dec 13, 2017 at 09:01:50AM -0800, Andy Lutomirski wrote:
> On Wed, Dec 13, 2017 at 5:12 AM, Kirill A. Shutemov
> <kirill@...temov.name> wrote:
> > On Tue, Dec 12, 2017 at 07:56:38AM -0800, Andy Lutomirski wrote:
> >> The ESPFIX64 user mapping belongs in pti.c just like all the other
> >> user mappings.  Move it there and make it work correctly while we're
> >> at it.
> >>
> >> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> >
> > Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> >
> > BTW, why do we open-code p?d_alloc() in pti_user_pagetable_walk_*()?
> > It seems unnecessary and potentially bogus: see smp_wmb() in __p?d_alloc()
> > helpers.
> 
> The helpers won't work -- we're allocating kernel-owned tables in the
> usermode part of init_mm.  The p?d_alloc() helpers allocate
> user-accounted tables in the kernelmode part of the mm.

What's wrong to account them against init_mm?

-- 
 Kirill A. Shutemov