powerpc/mm: Replace _PAGE_USER with _PAGE_PRIVILEGED

_PAGE_PRIVILEGED means the page can be accessed only by the kernel. This
is done to keep pte bits similar to PowerISA 3.0 Radix PTE format. User
pages are now marked by clearing _PAGE_PRIVILEGED bit.

Previously we allowed the kernel to have a privileged page in the lower
address range (USER_REGION). With this patch such access is denied.

We also prevent a kernel access to a non-privileged page in higher
address range (ie, REGION_ID != 0).

Both the above access scenarios should never happen.

Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Jeremy Kerr <jk@ozlabs.org>
Cc: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Acked-by: Ian Munsie <imunsie@au1.ibm.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 10 insertions, 6 deletions

diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
index 36e00371ba5a..dc0f6a00ccbd 100644
--- a/arch/powerpc/mm/hash_utils_64.c
+++ b/arch/powerpc/mm/hash_utils_64.c
@@ -174,7 +174,7 @@ unsigned long htab_convert_pte_flags(unsigned long pteflags)
 	 * User area is mapped with PP=0x2 for read/write
 	 * or PP=0x3 for read-only (including writeable but clean pages).
 	 */
-	if (pteflags & _PAGE_USER) {
+	if (!(pteflags & _PAGE_PRIVILEGED)) {
 		if (pteflags & _PAGE_RWX)
 			rflags |= 0x2;
 		if (!((pteflags & _PAGE_WRITE) && (pteflags & _PAGE_DIRTY)))
@@ -1090,7 +1090,7 @@ int hash_page_mm(struct mm_struct *mm, unsigned long ea,
 	/* Pre-check access permissions (will be re-checked atomically
 	 * in __hash_page_XX but this pre-check is a fast path
 	 */
-	if (access & ~pte_val(*ptep)) {
+	if (!check_pte_access(access, pte_val(*ptep))) {
 		DBG_LOW(" no access !\n");
 		rc = 1;
 		goto bail;
@@ -1228,12 +1228,16 @@ int __hash_page(unsigned long ea, unsigned long msr, unsigned long trap,
 	if (dsisr & DSISR_ISSTORE)
 		access |= _PAGE_WRITE;
 	/*
-	 * We need to set the _PAGE_USER bit if MSR_PR is set or if we are
-	 * accessing a userspace segment (even from the kernel). We assume
-	 * kernel addresses always have the high bit set.
+	 * We set _PAGE_PRIVILEGED only when
+	 * kernel mode access kernel space.
+	 *
+	 * _PAGE_PRIVILEGED is NOT set
+	 * 1) when kernel mode access user space
+	 * 2) user space access kernel space.
 	 */
+	access |= _PAGE_PRIVILEGED;
 	if ((msr & MSR_PR) || (REGION_ID(ea) == USER_REGION_ID))
-		access |= _PAGE_USER;
+		access &= ~_PAGE_PRIVILEGED;
 
 	if (trap == 0x400)
 		access |= _PAGE_EXEC;