This is a note to let you know that I've just added the patch titled x86/pti: Make unpoison of pgd for trusted boot work for real to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: x86-pti-make-unpoison-of-pgd-for-trusted-boot-work-for-real.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 445b69e3b75e42362a5bdc13c8b8f61599e2228a Mon Sep 17 00:00:00 2001 From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Date: Wed, 10 Jan 2018 14:49:39 -0800 Subject: x86/pti: Make unpoison of pgd for trusted boot work for real 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 ] [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.] 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 Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/kernel/tboot.c | 10 ++++++++++ 1 file changed, 10 insertions(+) --- a/arch/x86/kernel/tboot.c +++ b/arch/x86/kernel/tboot.c @@ -140,6 +140,16 @@ static int map_tboot_page(unsigned long return -1; set_pte_at(&tboot_mm, vaddr, pte, pfn_pte(pfn, prot)); pte_unmap(pte); + + /* + * PTI poisons low addresses in the kernel page tables in the + * name of making them unusable for userspace. To execute + * code at such a low address, the poison must be cleared. + * + * Note: 'pgd' actually gets set in pud_alloc(). + */ + pgd->pgd &= ~_PAGE_NX; + return 0; } Patches currently in stable-queue which might be from dave.hansen@xxxxxxxxxxxxxxx are queue-4.4/x86-pti-make-unpoison-of-pgd-for-trusted-boot-work-for-real.patch