s390/signal: set correct address space control
If user space is running in primary mode it can switch to secondary
or access register mode, this is used e.g. in the clock_gettime code
of the vdso. If a signal is delivered to the user space process while
it has been running in access register mode the signal handler is
executed in access register mode as well which will result in a crash
most of the time.
Set the address space control bits in the PSW to the default for the
execution of the signal handler and make sure that the previous
address space control is restored on signal return. Take care
that user space can not switch to the kernel address space by
modifying the registers in the signal frame.
Cc: stable@vger.kernel.org
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/arch/s390/kernel/signal.c b/arch/s390/kernel/signal.c
index c13a2a3..d1259d8 100644
--- a/arch/s390/kernel/signal.c
+++ b/arch/s390/kernel/signal.c
@@ -136,6 +136,10 @@
/* Use regs->psw.mask instead of psw_user_bits to preserve PER bit. */
regs->psw.mask = (regs->psw.mask & ~PSW_MASK_USER) |
(user_sregs.regs.psw.mask & PSW_MASK_USER);
+ /* Check for invalid user address space control. */
+ if ((regs->psw.mask & PSW_MASK_ASC) >= (psw_kernel_bits & PSW_MASK_ASC))
+ regs->psw.mask = (psw_user_bits & PSW_MASK_ASC) |
+ (regs->psw.mask & ~PSW_MASK_ASC);
/* Check for invalid amode */
if (regs->psw.mask & PSW_MASK_EA)
regs->psw.mask |= PSW_MASK_BA;
@@ -273,7 +277,10 @@
/* Set up registers for signal handler */
regs->gprs[15] = (unsigned long) frame;
- regs->psw.mask |= PSW_MASK_EA | PSW_MASK_BA; /* 64 bit amode */
+ /* Force default amode and default user address space control. */
+ regs->psw.mask = PSW_MASK_EA | PSW_MASK_BA |
+ (psw_user_bits & PSW_MASK_ASC) |
+ (regs->psw.mask & ~PSW_MASK_ASC);
regs->psw.addr = (unsigned long) ka->sa.sa_handler | PSW_ADDR_AMODE;
regs->gprs[2] = map_signal(sig);
@@ -346,7 +353,10 @@
/* Set up registers for signal handler */
regs->gprs[15] = (unsigned long) frame;
- regs->psw.mask |= PSW_MASK_EA | PSW_MASK_BA; /* 64 bit amode */
+ /* Force default amode and default user address space control. */
+ regs->psw.mask = PSW_MASK_EA | PSW_MASK_BA |
+ (psw_user_bits & PSW_MASK_ASC) |
+ (regs->psw.mask & ~PSW_MASK_ASC);
regs->psw.addr = (unsigned long) ka->sa.sa_handler | PSW_ADDR_AMODE;
regs->gprs[2] = map_signal(sig);