[PATCH 5/5] x86, pti: filter at vma->vm_page_prot population

Dave Hansen
2018-04-20T22:20:28Z

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

0day reported warnings at boot on 32-bit systems without NX support:

[ 12.349193] attempted to set unsupported pgprot: 8000000000000025 bits: 8000000000000000 supported: 7fffffffffffffff
[ 12.350792] WARNING: CPU: 0 PID: 1 at arch/x86/include/asm/pgtable.h:540 handle_mm_fault+0xfc1/0xfe0:
check_pgprot at arch/x86/include/asm/pgtable.h:535
(inlined by) pfn_pte at arch/x86/include/asm/pgtable.h:549
(inlined by) do_anonymous_page at mm/memory.c:3169
(inlined by) handle_pte_fault at mm/memory.c:3961
(inlined by) __handle_mm_fault at mm/memory.c:4087
(inlined by) handle_mm_fault at mm/memory.c:4124

The problem was that we stopped massaging page permissions at PTE creation
time, so vma->vm_page_prot was passed unfiltered to PTE creation.

To fix it, filter the page protections before they are installed in
vma->vm_page_prot.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Fixes: fb43d6cb91 ("x86/mm: Do not auto-massage page protections")
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Kees Cook <keescook@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nadav Amit <namit@vmware.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mm@kvack.org
Cc: Ingo Molnar <mingo@kernel.org>
---

b/arch/x86/Kconfig | 4 ++++
b/arch/x86/include/asm/pgtable.h | 5 +++++
b/mm/mmap.c | 11 ++++++++++-
3 files changed, 19 insertions(+), 1 deletion(-)

diff -puN arch/x86/include/asm/pgtable.h~pti-glb-protection_map arch/x86/include/asm/pgtable.h
--- a/arch/x86/include/asm/pgtable.h~pti-glb-protection_map 2018-04-20 14:10:08.251749151 -0700
+++ b/arch/x86/include/asm/pgtable.h 2018-04-20 14:10:08.260749151 -0700
@@ -601,6 +601,11 @@ static inline pgprot_t pgprot_modify(pgp

#define canon_pgprot(p) __pgprot(massage_pgprot(p))

+static inline pgprot_t arch_filter_pgprot(pgprot_t prot)
+{
+ return canon_pgprot(prot);
+}
+
static inline int is_new_memtype_allowed(u64 paddr, unsigned long size,
enum page_cache_mode pcm,
enum page_cache_mode new_pcm)
diff -puN arch/x86/Kconfig~pti-glb-protection_map arch/x86/Kconfig
--- a/arch/x86/Kconfig~pti-glb-protection_map 2018-04-20 14:10:08.253749151 -0700
+++ b/arch/x86/Kconfig 2018-04-20 14:10:08.260749151 -0700
@@ -52,6 +52,7 @@ config X86
select ARCH_HAS_DEVMEM_IS_ALLOWED
select ARCH_HAS_ELF_RANDOMIZE
select ARCH_HAS_FAST_MULTIPLIER
+ select ARCH_HAS_FILTER_PGPROT
select ARCH_HAS_FORTIFY_SOURCE
select ARCH_HAS_GCOV_PROFILE_ALL
select ARCH_HAS_KCOV if X86_64
@@ -273,6 +274,9 @@ config ARCH_HAS_CPU_RELAX
config ARCH_HAS_CACHE_LINE_SIZE
def_bool y

+config ARCH_HAS_FILTER_PGPROT
+ def_bool y
+
config HAVE_SETUP_PER_CPU_AREA
def_bool y

diff -puN mm/mmap.c~pti-glb-protection_map mm/mmap.c
--- a/mm/mmap.c~pti-glb-protection_map 2018-04-20 14:10:08.256749151 -0700
+++ b/mm/mmap.c 2018-04-20 14:10:08.261749151 -0700
@@ -100,11 +100,20 @@ pgprot_t protection_map[16] __ro_after_i
__S000, __S001, __S010, __S011, __S100, __S101, __S110, __S111
};

+#ifndef CONFIG_ARCH_HAS_FILTER_PGPROT
+static inline pgprot_t arch_filter_pgprot(pgprot_t prot)
+{
+ return prot;
+}
+#endif
+
pgprot_t vm_get_page_prot(unsigned long vm_flags)
{
- return __pgprot(pgprot_val(protection_map[vm_flags &
+ pgprot_t ret = __pgprot(pgprot_val(protection_map[vm_flags &
(VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]) |
pgprot_val(arch_vm_get_page_prot(vm_flags)));
+
+ return arch_filter_pgprot(ret);
}
EXPORT_SYMBOL(vm_get_page_prot);

_