On Mon, Jan 29, 2018 at 06:16:18PM -0800, Hugh Dickins wrote:
> From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxxx>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Reviewed-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Cc: Jon Masters <jcm@xxxxxxxxxx>
> Cc: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
> Cc: gnomes@xxxxxxxxxxxxxxxxxxx
> Cc: peterz@xxxxxxxxxxxxx
> Cc: ning.sun@xxxxxxxxx
> Cc: tboot-devel@xxxxxxxxxxxxxxxxxxxxx
> Cc: andi@xxxxxxxxxxxxxx
> Cc: luto@xxxxxxxxxx
> Cc: law@xxxxxxxxxx
> Cc: pbonzini@xxxxxxxxxx
> Cc: torvalds@xxxxxxxxxxxxxxxxxxxx
> Cc: gregkh@xxxxxxxxxxxxxxxxxxxx
> Cc: dwmw@xxxxxxxxxxxx
> Cc: nickc@xxxxxxxxxx
> Cc: stable@xxxxxxxxxxxxxxx
> Link: https://lkml.kernel.org/r/20180110224939.2695CD47@xxxxxxxxxxxxxxxxxx
> Cc: Jiri Kosina <jkosina@xxxxxxx>
> Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
>
> 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