ARM: kprobes: Reject probing of undefined data processing instructions

The instruction decoding in space_cccc_000x needs to reject probing of
instructions with undefined patterns as they may in future become
defined and then emulated faultily - as has already happened with the
SMC instruction.

This fix is achieved by testing for the instruction patterns we want to
probe and making the the default fall-through paths reject probes. This
also allows us to remove some explicit tests for instructions that we
wish to reject, as that is now the default action.

Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Nicolas Pitre <nicolas.pitre@linaro.org>

1 files changed, 17 insertions, 14 deletions

diff --git a/arch/arm/kernel/kprobes-decode.c b/arch/arm/kernel/kprobes-decode.c
index dc315c12d5f3..4715537b490c 100644
--- a/arch/arm/kernel/kprobes-decode.c
+++ b/arch/arm/kernel/kprobes-decode.c
@@ -966,14 +966,6 @@ space_cccc_000x(kprobe_opcode_t insn, struct arch_specific_insn *asi)
         /* cccc 0001 0xx0 xxxx xxxx xxxx xxxx xxx0 xxxx */
         if ((insn & 0x0f900010) == 0x01000000) {
 
-                /* BXJ      : cccc 0001 0010 xxxx xxxx xxxx 0010 xxxx */
-                /* MSR      : cccc 0001 0x10 xxxx xxxx xxxx 0000 xxxx */
-                /* MRS spsr : cccc 0001 0100 xxxx xxxx xxxx 0000 xxxx */
-                if ((insn & 0x0ff000f0) == 0x01200020 ||
-                    (insn & 0x0fb000f0) == 0x01200000 ||
-                    (insn & 0x0ff000f0) == 0x01400000)
-                        return INSN_REJECTED;
-
                 /* MRS cpsr : cccc 0001 0000 xxxx xxxx xxxx 0000 xxxx */
                 if ((insn & 0x0ff000f0) == 0x01000000) {
                         if (is_r15(insn, 12))
@@ -994,17 +986,21 @@ space_cccc_000x(kprobe_opcode_t insn, struct arch_specific_insn *asi)
 
                 /* SMLAxy : cccc 0001 0000 xxxx xxxx xxxx 1xx0 xxxx : Q */
                 /* SMLAWy : cccc 0001 0010 xxxx xxxx xxxx 1x00 xxxx : Q */
-                return prep_emulate_rd16rn12rs8rm0_wflags(insn, asi);
+                if ((insn & 0x0ff00090) == 0x01000080 ||
+                    (insn & 0x0ff000b0) == 0x01200080)
+                        return prep_emulate_rd16rn12rs8rm0_wflags(insn, asi);
+
+                /* BXJ      : cccc 0001 0010 xxxx xxxx xxxx 0010 xxxx */
+                /* MSR      : cccc 0001 0x10 xxxx xxxx xxxx 0000 xxxx */
+                /* MRS spsr : cccc 0001 0100 xxxx xxxx xxxx 0000 xxxx */
 
+                /* Other instruction encodings aren't yet defined */
+                return INSN_REJECTED;
         }
 
         /* cccc 0001 0xx0 xxxx xxxx xxxx xxxx 0xx1 xxxx */
         else if ((insn & 0x0f900090) == 0x01000010) {
 
-                /* BKPT : 1110 0001 0010 xxxx xxxx xxxx 0111 xxxx */
-                if ((insn & 0xfff000f0) == 0xe1200070)
-                        return INSN_REJECTED;
-
                 /* BLX(2) : cccc 0001 0010 xxxx xxxx xxxx 0011 xxxx */
                 /* BX     : cccc 0001 0010 xxxx xxxx xxxx 0001 xxxx */
                 if ((insn & 0x0ff000d0) == 0x01200010) {
@@ -1022,7 +1018,14 @@ space_cccc_000x(kprobe_opcode_t insn, struct arch_specific_insn *asi)
                 /* QSUB    : cccc 0001 0010 xxxx xxxx xxxx 0101 xxxx :Q */
                 /* QDADD   : cccc 0001 0100 xxxx xxxx xxxx 0101 xxxx :Q */
                 /* QDSUB   : cccc 0001 0110 xxxx xxxx xxxx 0101 xxxx :Q */
-                return prep_emulate_rd12rn16rm0_wflags(insn, asi);
+                if ((insn & 0x0f9000f0) == 0x01000050)
+                        return prep_emulate_rd12rn16rm0_wflags(insn, asi);
+
+                /* BKPT : 1110 0001 0010 xxxx xxxx xxxx 0111 xxxx */
+                /* SMC  : cccc 0001 0110 xxxx xxxx xxxx 0111 xxxx */
+
+                /* Other instruction encodings aren't yet defined */
+                return INSN_REJECTED;
         }
 
         /* cccc 0000 xxxx xxxx xxxx xxxx xxxx 1001 xxxx */