4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: John David Anglin <dave.anglin@xxxxxxxx> commit 6ed518328d0189e0fdf1bb7c73290d546143ea66 upstream. 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. Signed-off-by: John David Anglin <dave.anglin@xxxxxxxx> Signed-off-by: Helge Deller <deller@xxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/parisc/kernel/syscall.S | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) --- 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 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html