[PATCH RFC v2 2/6] x86: Save pti_disable for each mm_context

Nadav Amit
2018-02-15T16:37:30Z

Save for each mm->context whether page-table isolation should be
disabled. In order not to make intrusive changes, the information is
saved in the PGD page metadata.

Signed-off-by: Nadav Amit <namit@vmware.com>
---
arch/x86/include/asm/mmu.h | 3 +++
arch/x86/include/asm/pti.h | 9 +++++++++
arch/x86/mm/pgtable.c | 4 +++-
arch/x86/mm/pti.c | 9 +++++++--
4 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/mmu.h b/arch/x86/include/asm/mmu.h
index 5ff3e8af2c20..fb8db4a09d8a 100644
--- a/arch/x86/include/asm/mmu.h
+++ b/arch/x86/include/asm/mmu.h
@@ -36,6 +36,9 @@ typedef struct {
/* True if mm supports a task running in 32 bit compatibility mode. */
unsigned short ia32_compat;
#endif
+#ifdef CONFIG_PAGE_TABLE_ISOLATION
+ unsigned short pti_disable;
+#endif

struct mutex lock;
void __user *vdso; /* vdso base address */
diff --git a/arch/x86/include/asm/pti.h b/arch/x86/include/asm/pti.h
index 0b5ef05b2d2d..96a5fbfedf7a 100644
--- a/arch/x86/include/asm/pti.h
+++ b/arch/x86/include/asm/pti.h
@@ -4,9 +4,18 @@
#ifndef __ASSEMBLY__

#ifdef CONFIG_PAGE_TABLE_ISOLATION
+static inline unsigned short mm_pti_disable(struct mm_struct *mm)
+{
+ if (mm == NULL)
+ return 0;
+
+ return mm->context.pti_disable;
+}
+
extern void pti_init(void);
extern void pti_check_boottime_disable(void);
#else
+static inline unsigned short mm_pti_disable(struct mm_struct *mm) { return 0; }
static inline void pti_check_boottime_disable(void) { }
#endif

diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index 004abf9ebf12..ef0394a97adb 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -139,7 +139,9 @@ static void pgd_ctor(struct mm_struct *mm, pgd_t *pgd)
if (!SHARED_KERNEL_PMD) {
pgd_set_mm(pgd, mm);
pgd_list_add(pgd);
- }
+ } else if (IS_ENABLED(CONFIG_PAGE_TABLE_ISOLATION) &&
+ static_cpu_has(X86_FEATURE_PTI))
+ pgd_set_mm(pgd, mm);
}

static void pgd_dtor(pgd_t *pgd)
diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index ce38f165489b..a973a291a34d 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -134,10 +134,15 @@ pgd_t __pti_set_user_pgd(pgd_t *pgdp, pgd_t pgd)
* may execute from it
* - we don't have NX support
* - we're clearing the PGD (i.e. the new pgd is not present).
+ * - PTI is disabled.
*/
if ((pgd.pgd & (_PAGE_USER|_PAGE_PRESENT)) == (_PAGE_USER|_PAGE_PRESENT) &&
- (__supported_pte_mask & _PAGE_NX))
- pgd.pgd |= _PAGE_NX;
+ (__supported_pte_mask & _PAGE_NX)) {
+ struct mm_struct *mm = pgd_page_get_mm(virt_to_page(pgdp));
+
+ if (!mm_pti_disable(mm))
+ pgd.pgd |= _PAGE_NX;
+ }

/* return the copy of the PGD we want the kernel to use: */
return pgd;
--
2.14.1