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authorJohn David Anglin <dave.anglin@bell.net>2016-10-28 23:00:34 -0400
committerSasha Levin <alexander.levin@verizon.com>2016-11-23 23:09:24 -0500
commit056bcad97c8e1ac7f6287a45b090ea51f93565cf (patch)
tree8327d3050882c20ea58a62e4ee75f1ed9e9b9d03
parentdff2cd539e4b537bf2e929eea256b20cd5262b35 (diff)
downloadlinux-linaro-stable-056bcad97c8e1ac7f6287a45b090ea51f93565cf.tar.gz
parisc: Ensure consistent state when switching to kernel stack at syscall entry
[ Upstream commit 6ed518328d0189e0fdf1bb7c73290d546143ea66 ] We have one critical section in the syscall entry path in which we switch from the userspace stack to kernel stack. In the event of an external interrupt, the interrupt code distinguishes between those two states by analyzing the value of sr7. If sr7 is zero, it uses the kernel stack. Therefore it's important, that the value of sr7 is in sync with the currently enabled stack. This patch now disables interrupts while executing the critical section. This prevents the interrupt handler to possibly see an inconsistent state which in the worst case can lead to crashes. Interestingly, in the syscall exit path interrupts were already disabled in the critical section which switches back to the userspace stack. Cc: <stable@vger.kernel.org> Signed-off-by: John David Anglin <dave.anglin@bell.net> Signed-off-by: Helge Deller <deller@gmx.de> Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
-rw-r--r--arch/parisc/kernel/syscall.S11
1 files changed, 9 insertions, 2 deletions
diff --git a/arch/parisc/kernel/syscall.S b/arch/parisc/kernel/syscall.S
index 099c23616901..8f13c7facdd7 100644
--- a/arch/parisc/kernel/syscall.S
+++ b/arch/parisc/kernel/syscall.S
@@ -106,8 +106,6 @@ linux_gateway_entry:
mtsp %r0,%sr4 /* get kernel space into sr4 */
mtsp %r0,%sr5 /* get kernel space into sr5 */
mtsp %r0,%sr6 /* get kernel space into sr6 */
- mfsp %sr7,%r1 /* save user sr7 */
- mtsp %r1,%sr3 /* and store it in sr3 */
#ifdef CONFIG_64BIT
/* for now we can *always* set the W bit on entry to the syscall
@@ -133,6 +131,14 @@ linux_gateway_entry:
depdi 0, 31, 32, %r21
1:
#endif
+
+ /* We use a rsm/ssm pair to prevent sr3 from being clobbered
+ * by external interrupts.
+ */
+ mfsp %sr7,%r1 /* save user sr7 */
+ rsm PSW_SM_I, %r0 /* disable interrupts */
+ mtsp %r1,%sr3 /* and store it in sr3 */
+
mfctl %cr30,%r1
xor %r1,%r30,%r30 /* ye olde xor trick */
xor %r1,%r30,%r1
@@ -147,6 +153,7 @@ linux_gateway_entry:
*/
mtsp %r0,%sr7 /* get kernel space into sr7 */
+ ssm PSW_SM_I, %r0 /* enable interrupts */
STREGM %r1,FRAME_SIZE(%r30) /* save r1 (usp) here for now */
mfctl %cr30,%r1 /* get task ptr in %r1 */
LDREG TI_TASK(%r1),%r1