powerpc: Fix string instr. emulation for 32-bit processes on ppc64

String instruction emulation would erroneously result in a segfault if
the upper bits of the EA are set and is so high that it fails access
check.  Truncate the EA to 32 bits if the process is 32-bit.

Signed-off-by: James Yang <James.Yang@freescale.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 4 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 071f6e040eb2..300daf3e7ab0 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -866,6 +866,10 @@ static int emulate_string_inst(struct pt_regs *regs, u32 instword)
                 u8 val;
                 u32 shift = 8 * (3 - (pos & 0x3));
 
+                /* if process is 32-bit, clear upper 32 bits of EA */
+                if ((regs->msr & MSR_64BIT) == 0)
+                        EA &= 0xFFFFFFFF;
+
                 switch ((instword & PPC_INST_STRING_MASK)) {
                         case PPC_INST_LSWX:
                         case PPC_INST_LSWI: