[PATCH 06/23] x86, kaiser: allow NX poison to be set in p4d/pgd

Dave Hansen
2017-11-23T00:40:07Z

From: Dave Hansen <dave.hansen@linux.intel.com>

The user portion of the kernel page tables use the NX bit to
poison them for userspace. But, that trips the p4d/pgd_bad()
checks. Make sure it does not do that.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Moritz Lipp <moritz.lipp@iaik.tugraz.at>
Cc: Daniel Gruss <daniel.gruss@iaik.tugraz.at>
Cc: Michael Schwarz <michael.schwarz@iaik.tugraz.at>
Cc: Richard Fellner <richard.fellner@student.tugraz.at>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Kees Cook <keescook@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: x86@kernel.org
---

b/arch/x86/include/asm/pgtable.h | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)

diff -puN arch/x86/include/asm/pgtable.h~kaiser-p4d-allow-nx arch/x86/include/asm/pgtable.h
--- a/arch/x86/include/asm/pgtable.h~kaiser-p4d-allow-nx 2017-11-22 15:45:47.382619743 -0800
+++ b/arch/x86/include/asm/pgtable.h 2017-11-22 15:45:47.386619743 -0800
@@ -846,7 +846,12 @@ static inline pud_t *pud_offset(p4d_t *p

static inline int p4d_bad(p4d_t p4d)
{
- return (p4d_flags(p4d) & ~(_KERNPG_TABLE | _PAGE_USER)) != 0;
+ unsigned long ignore_flags = _KERNPG_TABLE | _PAGE_USER;
+
+ if (IS_ENABLED(CONFIG_KAISER))
+ ignore_flags |= _PAGE_NX;
+
+ return (p4d_flags(p4d) & ~ignore_flags) != 0;
}
#endif /* CONFIG_PGTABLE_LEVELS > 3 */

@@ -880,7 +885,12 @@ static inline p4d_t *p4d_offset(pgd_t *p

static inline int pgd_bad(pgd_t pgd)
{
- return (pgd_flags(pgd) & ~_PAGE_USER) != _KERNPG_TABLE;
+ unsigned long ignore_flags = _PAGE_USER;
+
+ if (IS_ENABLED(CONFIG_KAISER))
+ ignore_flags |= _PAGE_NX;
+
+ return (pgd_flags(pgd) & ~ignore_flags) != _KERNPG_TABLE;
}

static inline int pgd_none(pgd_t pgd)
_