MIPS: Fix branch emulation for BLTC and BGEC instructions

Commits f1b44067c19258b7614e3cd09dfe8d8e12ff5895 ("MIPS: Emulate the
new MIPS R6 B{L,G}T{Z,}{AL,}C instructions") and commit
a8ff66f52d3f17b5ae793955270675c197f73d6c ("MIPS: Emulate the new MIPS
R6 B{L,G}E{Z,}{AL,}C instructions") added support for emulating various
branch compact instructions. However, it missed the case for those which
use the old BLEZL and BGTZL opcodes leading to random crashes when the R6
emulator is disabled. We fix this by ensuring that the 'rt' field is not
zero which is always true for these branch compact instructions.

Fixes: f1b44067c192 ("MIPS: Emulate the new MIPS R6 B{L,G}T{Z,}{AL,}C instructions")
Fixes: a8ff66f52d3f ("MIPS: Emulate the new MIPS R6 B{L,G}E{Z,}{AL,}C instructions")
Cc: <stable@vger.kernel.org> # 4.0+
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: Markos Chandras <markos.chandras@imgtec.com>
Patchwork: https://patchwork.linux-mips.org/patch/10582/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

diff --git a/arch/mips/kernel/branch.c b/arch/mips/kernel/branch.c
index c0c5e5972256e95273d7e34a0b4c3c4132232cd0..d8f9b357b2226bef0141c8ed6340baa8fb7c0f4f 100644 (file)
--- a/arch/mips/kernel/branch.c
+++ b/arch/mips/kernel/branch.c
@@ -600,7 +600,7 @@ int __compute_return_epc_for_insn(struct pt_regs *regs,
                break;
 
        case blezl_op: /* not really i_format */
-               if (NO_R6EMU)
+               if (!insn.i_format.rt && NO_R6EMU)
                        goto sigill_r6;
        case blez_op:
                /*
@@ -635,7 +635,7 @@ int __compute_return_epc_for_insn(struct pt_regs *regs,
                break;
 
        case bgtzl_op:
-               if (NO_R6EMU)
+               if (!insn.i_format.rt && NO_R6EMU)
                        goto sigill_r6;
        case bgtz_op:
                /*

diff --git a/arch/mips/math-emu/cp1emu.c b/arch/mips/math-emu/cp1emu.c
index 22b9b2cb9219fa4e4eb7b9cc340125a4c9aa4053..00c241ae04ce83ea5d73977f5eb8a80eb35ded19 100644 (file)
--- a/arch/mips/math-emu/cp1emu.c
+++ b/arch/mips/math-emu/cp1emu.c
@@ -551,7 +551,7 @@ static int isBranchInstr(struct pt_regs *regs, struct mm_decoded_insn dec_insn,
                                dec_insn.next_pc_inc;
                return 1;
        case blezl_op:
-               if (NO_R6EMU)
+               if (!insn.i_format.rt && NO_R6EMU)
                        break;
        case blez_op:
 
@@ -588,7 +588,7 @@ static int isBranchInstr(struct pt_regs *regs, struct mm_decoded_insn dec_insn,
                                dec_insn.next_pc_inc;
                return 1;
        case bgtzl_op:
-               if (NO_R6EMU)
+               if (!insn.i_format.rt && NO_R6EMU)
                        break;
        case bgtz_op:
                /*