s390: fix handling of runtime instrumentation psw bit

Fix the following bugs:
- When returning from a signal the signal handler copies the saved psw mask
  from user space and uses parts of it. Especially it restores the RI bit
  unconditionally. If however the machine doesn't support RI, or RI is
  disabled for the task, the last lpswe instruction which returns to user
  space will generate a specification exception.
  To fix this check if the RI bit is allowed to be set and kill the task
  if not.
- In the compat mode signal handler code the RI bit of the psw mask gets
  propagated to the mask of the return psw: if user space enables RI in the
  signal handler, RI will also be enabled after the signal handler is
  finished.
  This is a different behaviour than with 64 bit tasks. So change this to
  match the 64 bit semantics, which restores the original RI bit value.
- Fix similar oddities within the ptrace code as well.

Reviewed-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 20 insertions, 10 deletions

diff --git a/arch/s390/kernel/ptrace.c b/arch/s390/kernel/ptrace.c
index 67db29efae32..1d1f9c30c5fa 100644
--- a/arch/s390/kernel/ptrace.c
+++ b/arch/s390/kernel/ptrace.c
@@ -198,9 +198,11 @@ static unsigned long __peek_user(struct task_struct *child, addr_t addr)
 		 * psw and gprs are stored on the stack
 		 */
 		tmp = *(addr_t *)((addr_t) &task_pt_regs(child)->psw + addr);
-		if (addr == (addr_t) &dummy->regs.psw.mask)
+		if (addr == (addr_t) &dummy->regs.psw.mask) {
 			/* Return a clean psw mask. */
-			tmp = PSW_USER_BITS | (tmp & PSW_MASK_USER);
+			tmp &= PSW_MASK_USER | PSW_MASK_RI;
+			tmp |= PSW_USER_BITS;
+		}
 
 	} else if (addr < (addr_t) &dummy->regs.orig_gpr2) {
 		/*
@@ -320,11 +322,15 @@ static int __poke_user(struct task_struct *child, addr_t addr, addr_t data)
 		/*
 		 * psw and gprs are stored on the stack
 		 */
-		if (addr == (addr_t) &dummy->regs.psw.mask &&
-		    ((data & ~PSW_MASK_USER) != PSW_USER_BITS ||
-		     ((data & PSW_MASK_EA) && !(data & PSW_MASK_BA))))
-			/* Invalid psw mask. */
-			return -EINVAL;
+		if (addr == (addr_t) &dummy->regs.psw.mask) {
+			unsigned long mask = PSW_MASK_USER;
+
+			mask |= is_ri_task(child) ? PSW_MASK_RI : 0;
+			if ((data & ~mask) != PSW_USER_BITS)
+				return -EINVAL;
+			if ((data & PSW_MASK_EA) && !(data & PSW_MASK_BA))
+				return -EINVAL;
+		}
 		*(addr_t *)((addr_t) &task_pt_regs(child)->psw + addr) = data;
 
 	} else if (addr < (addr_t) (&dummy->regs.orig_gpr2)) {
@@ -556,7 +562,8 @@ static u32 __peek_user_compat(struct task_struct *child, addr_t addr)
 		if (addr == (addr_t) &dummy32->regs.psw.mask) {
 			/* Fake a 31 bit psw mask. */
 			tmp = (__u32)(regs->psw.mask >> 32);
-			tmp = psw32_user_bits | (tmp & PSW32_MASK_USER);
+			tmp &= PSW32_MASK_USER | PSW32_MASK_RI;
+			tmp |= psw32_user_bits;
 		} else if (addr == (addr_t) &dummy32->regs.psw.addr) {
 			/* Fake a 31 bit psw address. */
 			tmp = (__u32) regs->psw.addr |
@@ -653,13 +660,16 @@ static int __poke_user_compat(struct task_struct *child,
 		 * psw, gprs, acrs and orig_gpr2 are stored on the stack
 		 */
 		if (addr == (addr_t) &dummy32->regs.psw.mask) {
+			__u32 mask = PSW32_MASK_USER;
+
+			mask |= is_ri_task(child) ? PSW32_MASK_RI : 0;
 			/* Build a 64 bit psw mask from 31 bit mask. */
-			if ((tmp & ~PSW32_MASK_USER) != psw32_user_bits)
+			if ((tmp & ~mask) != psw32_user_bits)
 				/* Invalid psw mask. */
 				return -EINVAL;
 			regs->psw.mask = (regs->psw.mask & ~PSW_MASK_USER) |
 				(regs->psw.mask & PSW_MASK_BA) |
-				(__u64)(tmp & PSW32_MASK_USER) << 32;
+				(__u64)(tmp & mask) << 32;
 		} else if (addr == (addr_t) &dummy32->regs.psw.addr) {
 			/* Build a 64 bit psw address from 31 bit address. */
 			regs->psw.addr = (__u64) tmp & PSW32_ADDR_INSN;