ARM: kprobes: Add emulation of hint instructions like NOP and WFI

Being able to probe NOP instructions is useful for hard-coding probeable
locations and is used by the kprobes test code.

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

1 files changed, 24 insertions, 0 deletions

diff --git a/arch/arm/kernel/kprobes-decode.c b/arch/arm/kernel/kprobes-decode.c
index 6bed8b089af0..03b85ad525ab 100644
--- a/arch/arm/kernel/kprobes-decode.c
+++ b/arch/arm/kernel/kprobes-decode.c
@@ -1225,6 +1225,30 @@ space_cccc_001x(kprobe_opcode_t insn, struct arch_specific_insn *asi)
         if ((insn & 0x0fb00000) == 0x03000000)
                 return prep_emulate_rd12_modify(insn, asi);
 
+        /* hints : cccc 0011 0010 0000 xxxx xxxx xxxx xxxx */
+        if ((insn & 0x0fff0000) == 0x03200000) {
+                unsigned op2 = insn & 0x000000ff;
+                if (op2 == 0x01 || op2 == 0x04) {
+                        /* YIELD : cccc 0011 0010 0000 xxxx xxxx 0000 0001 */
+                        /* SEV   : cccc 0011 0010 0000 xxxx xxxx 0000 0100 */
+                        asi->insn[0] = insn;
+                        asi->insn_handler = emulate_none;
+                        return INSN_GOOD;
+                } else if (op2 <= 0x03) {
+                        /* NOP   : cccc 0011 0010 0000 xxxx xxxx 0000 0000 */
+                        /* WFE   : cccc 0011 0010 0000 xxxx xxxx 0000 0010 */
+                        /* WFI   : cccc 0011 0010 0000 xxxx xxxx 0000 0011 */
+                        /*
+                         * We make WFE and WFI true NOPs to avoid stalls due
+                         * to missing events whilst processing the probe.
+                         */
+                        asi->insn_handler = emulate_nop;
+                        return INSN_GOOD_NO_SLOT;
+                }
+                /* For DBG and unallocated hints it's safest to reject them */
+                return INSN_REJECTED;
+        }
+
         /*
          * MSR   : cccc 0011 0x10 xxxx xxxx xxxx xxxx xxxx
          * ALU op with S bit and Rd == 15 :