arm64: kprobes instruction simulation support

Kprobes needs simulation of instructions that cannot be stepped
from a different memory location, e.g.: those instructions
that uses PC-relative addressing. In simulation, the behaviour
of the instruction is implemented using a copy of pt_regs.

The following instruction categories are simulated:
 - All branching instructions(conditional, register, and immediate)
 - Literal access instructions(load-literal, adr/adrp)

Conditional execution is limited to branching instructions in
ARM v8. If conditions at PSTATE do not match the condition fields
of opcode, the instruction is effectively NOP.

Thanks to Will Cohen for assorted suggested changes.

Signed-off-by: Sandeepa Prabhu <sandeepa.s.prabhu@gmail.com>
Signed-off-by: William Cohen <wcohen@redhat.com>
Signed-off-by: David A. Long <dave.long@linaro.org>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
[catalin.marinas@arm.com: removed linux/module.h include]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

1 files changed, 32 insertions, 1 deletions

diff --git a/arch/arm64/kernel/probes/decode-insn.c b/arch/arm64/kernel/probes/decode-insn.c
index 95c0c5281e7b..37e47a9d617e 100644
--- a/arch/arm64/kernel/probes/decode-insn.c
+++ b/arch/arm64/kernel/probes/decode-insn.c
@@ -21,6 +21,7 @@
 #include <asm/sections.h>
 
 #include "decode-insn.h"
+#include "simulate-insn.h"
 
 static bool __kprobes aarch64_insn_is_steppable(u32 insn)
 {
@@ -74,6 +75,7 @@ static bool __kprobes aarch64_insn_is_steppable(u32 insn)
 /* Return:
  *   INSN_REJECTED     If instruction is one not allowed to kprobe,
  *   INSN_GOOD         If instruction is supported and uses instruction slot,
+ *   INSN_GOOD_NO_SLOT If instruction is supported but doesn't use its slot.
  */
 static enum kprobe_insn __kprobes
 arm_probe_decode_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi)
@@ -84,8 +86,37 @@ arm_probe_decode_insn(kprobe_opcode_t insn, struct arch_specific_insn *asi)
 	 */
 	if (aarch64_insn_is_steppable(insn))
 		return INSN_GOOD;
-	else
+
+	if (aarch64_insn_is_bcond(insn)) {
+		asi->handler = simulate_b_cond;
+	} else if (aarch64_insn_is_cbz(insn) ||
+	    aarch64_insn_is_cbnz(insn)) {
+		asi->handler = simulate_cbz_cbnz;
+	} else if (aarch64_insn_is_tbz(insn) ||
+	    aarch64_insn_is_tbnz(insn)) {
+		asi->handler = simulate_tbz_tbnz;
+	} else if (aarch64_insn_is_adr_adrp(insn)) {
+		asi->handler = simulate_adr_adrp;
+	} else if (aarch64_insn_is_b(insn) ||
+	    aarch64_insn_is_bl(insn)) {
+		asi->handler = simulate_b_bl;
+	} else if (aarch64_insn_is_br(insn) ||
+	    aarch64_insn_is_blr(insn) ||
+	    aarch64_insn_is_ret(insn)) {
+		asi->handler = simulate_br_blr_ret;
+	} else if (aarch64_insn_is_ldr_lit(insn)) {
+		asi->handler = simulate_ldr_literal;
+	} else if (aarch64_insn_is_ldrsw_lit(insn)) {
+		asi->handler = simulate_ldrsw_literal;
+	} else {
+		/*
+		 * Instruction cannot be stepped out-of-line and we don't
+		 * (yet) simulate it.
+		 */
 		return INSN_REJECTED;
+	}
+
+	return INSN_GOOD_NO_SLOT;
 }
 
 static bool __kprobes