Date: Thu, 1 Feb 2018 09:09:13 +0100
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Hugh Dickins <hughd@google.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Jon Masters <jcm@redhat.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        gnomes@lxorguk.ukuu.org.uk, peterz@infradead.org,
        ning.sun@intel.com, tboot-devel@lists.sourceforge.net,
        andi@firstfloor.org, luto@kernel.org, law@redhat.com,
        pbonzini@redhat.com, torvalds@linux-foundation.org,
        dwmw@amazon.co.uk, nickc@redhat.com, stable@vger.kernel.org,
        Jiri Kosina <jkosina@suse.cz>
Subject: Re: [PATCH 4.4] x86/pti: Make unpoison of pgd for trusted boot work
 for real
Message-ID: <20180201080913.GB15896@kroah.com>
References: <20180130021618.228975-1-hughd@google.com>
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Sender: stable-owner@vger.kernel.org

On Mon, Jan 29, 2018 at 06:16:18PM -0800, Hugh Dickins wrote:
> From: Dave Hansen <dave.hansen@linux.intel.com>
> 
> commit 445b69e3b75e42362a5bdc13c8b8f61599e2228a upstream
> 
> The inital fix for trusted boot and PTI potentially misses the pgd clearing
> if pud_alloc() sets a PGD.  It probably works in *practice* because for two
> adjacent calls to map_tboot_page() that share a PGD entry, the first will
> clear NX, *then* allocate and set the PGD (without NX clear).  The second
> call will *not* allocate but will clear the NX bit.
> 
> Defer the NX clearing to a point after it is known that all top-level
> allocations have occurred.  Add a comment to clarify why.
> 
> [ tglx: Massaged changelog ]
> 
> Fixes: 262b6b30087 ("x86/tboot: Unbreak tboot with PTI enabled")
> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
> Cc: Jon Masters <jcm@redhat.com>
> Cc: Tim Chen <tim.c.chen@linux.intel.com>
> Cc: gnomes@lxorguk.ukuu.org.uk
> Cc: peterz@infradead.org
> Cc: ning.sun@intel.com
> Cc: tboot-devel@lists.sourceforge.net
> Cc: andi@firstfloor.org
> Cc: luto@kernel.org
> Cc: law@redhat.com
> Cc: pbonzini@redhat.com
> Cc: torvalds@linux-foundation.org
> Cc: gregkh@linux-foundation.org
> Cc: dwmw@amazon.co.uk
> Cc: nickc@redhat.com
> Cc: stable@vger.kernel.org
> Link: https://lkml.kernel.org/r/20180110224939.2695CD47@viggo.jf.intel.com
> Cc: Jiri Kosina <jkosina@suse.cz>
> Signed-off-by: Hugh Dickins <hughd@google.com>
> 
> hughd notes: I have not tested tboot, but this looks to me as necessary
> and as safe in old-Kaiser backports as it is upstream; I'm not submitting
> the commit-to-be-fixed 262b6b30087, since it was undone by 445b69e3b75e,
> and makes conflict trouble because of 5-level's p4d versus 4-level's pgd.

Thanks for the backport, now queued up.

greg k-h