[PATCH 4.1 012/123] MIPS: Fix erroneous JR emulation for MIPS R6

From: Greg Kroah-Hartman
Date: Sat Aug 08 2015 - 18:12:10 EST

4.1-stable review patch. If anyone has any objections, please let me know.


From: Markos Chandras <markos.chandras@xxxxxxxxxx>

commit 143fefc8f315cd10e046e6860913c421c3385cb1 upstream.

Commit 5f9f41c474befb4ebbc40b27f65bb7d649241581 ("MIPS: kernel: Prepare
the JR instruction for emulation on MIPS R6") added support for
emulating the JR instruction on MIPS R6 cores but that introduced a bug
which could be triggered when hitting a JALR opcode because the code used
the wrong field in the 'r_format' struct to determine the instruction
opcode. This lead to crashes because an emulated JALR instruction was
treated as a JR one when the R6 emulator was turned off.

Fixes: 5f9f41c474be ("MIPS: kernel: Prepare the JR instruction for emulation on MIPS R6")
Signed-off-by: Markos Chandras <markos.chandras@xxxxxxxxxx>
Cc: linux-mips@xxxxxxxxxxxxxx
Patchwork: https://patchwork.linux-mips.org/patch/10583/
Signed-off-by: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

arch/mips/math-emu/cp1emu.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/mips/math-emu/cp1emu.c
+++ b/arch/mips/math-emu/cp1emu.c
@@ -451,7 +451,7 @@ static int isBranchInstr(struct pt_regs
/* Fall through */
case jr_op:
/* For R6, JR already emulated in jalr_op */
- if (NO_R6EMU && insn.r_format.opcode == jr_op)
+ if (NO_R6EMU && insn.r_format.func == jr_op)
*contpc = regs->regs[insn.r_format.rs];
return 1;

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