x86/bugs: Expose /sys/../spec_store_bypass

[mirror_ubuntu-bionic-kernel.git] / arch / x86 / kernel / tboot.c

diff --git a/arch/x86/kernel/tboot.c b/arch/x86/kernel/tboot.c
index a4eb27918cebf99dc2415f7eec49c4838d6f9f41..a2486f4440734756d49a96313c0e2f9a174a87db 100644 (file)
--- a/arch/x86/kernel/tboot.c
+++ b/arch/x86/kernel/tboot.c
@@ -138,6 +138,17 @@ static int map_tboot_page(unsigned long vaddr, unsigned long pfn,
                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 p4d_alloc() _or_
+        * pud_alloc() depending on 4/5-level paging.
+        */
+       pgd->pgd &= ~_PAGE_NX;
+
        return 0;
 }