ARM: kprobes: introduces checker

This patch introdces 'checker' to decoding phase, and calls checkers
when instruction decoding. This allows further decoding for specific
instructions.  This patch introduces a stub call of checkers in kprobe
arch_prepare_kprobe() as an example and for further expansion.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Reviewed-by: Jon Medhurst <tixy@linaro.org>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Jon Medhurst <tixy@linaro.org>

1 files changed, 54 insertions, 6 deletions

diff --git a/arch/arm/probes/decode.c b/arch/arm/probes/decode.c
index 3b05d5742359..c7d442018902 100644
--- a/arch/arm/probes/decode.c
+++ b/arch/arm/probes/decode.c
@@ -342,6 +342,31 @@ static const int decode_struct_sizes[NUM_DECODE_TYPES] = {
         [DECODE_TYPE_REJECT]    = sizeof(struct decode_reject)
 };
 
+static int run_checkers(const struct decode_checker *checkers[],
+                int action, probes_opcode_t insn,
+                struct arch_probes_insn *asi,
+                const struct decode_header *h)
+{
+        const struct decode_checker **p;
+
+        if (!checkers)
+                return INSN_GOOD;
+
+        p = checkers;
+        while (*p != NULL) {
+                int retval;
+                probes_check_t *checker_func = (*p)[action].checker;
+
+                retval = INSN_GOOD;
+                if (checker_func)
+                        retval = checker_func(insn, asi, h);
+                if (retval == INSN_REJECTED)
+                        return retval;
+                p++;
+        }
+        return INSN_GOOD;
+}
+
 /*
  * probes_decode_insn operates on data tables in order to decode an ARM
  * architecture instruction onto which a kprobe has been placed.
@@ -388,11 +413,17 @@ static const int decode_struct_sizes[NUM_DECODE_TYPES] = {
 int __kprobes
 probes_decode_insn(probes_opcode_t insn, struct arch_probes_insn *asi,
                    const union decode_item *table, bool thumb,
-                   bool emulate, const union decode_action *actions)
+                   bool emulate, const union decode_action *actions,
+                   const struct decode_checker *checkers[])
 {
         const struct decode_header *h = (struct decode_header *)table;
         const struct decode_header *next;
         bool matched = false;
+        /*
+         * @insn can be modified by decode_regs. Save its original
+         * value for checkers.
+         */
+        probes_opcode_t origin_insn = insn;
 
         if (emulate)
                 insn = prepare_emulated_insn(insn, asi, thumb);
@@ -422,24 +453,41 @@ probes_decode_insn(probes_opcode_t insn, struct arch_probes_insn *asi,
                 }
 
                 case DECODE_TYPE_CUSTOM: {
+                        int err;
                         struct decode_custom *d = (struct decode_custom *)h;
-                        return actions[d->decoder.action].decoder(insn, asi, h);
+                        int action = d->decoder.action;
+
+                        err = run_checkers(checkers, action, origin_insn, asi, h);
+                        if (err == INSN_REJECTED)
+                                return INSN_REJECTED;
+                        return actions[action].decoder(insn, asi, h);
                 }
 
                 case DECODE_TYPE_SIMULATE: {
+                        int err;
                         struct decode_simulate *d = (struct decode_simulate *)h;
-                        asi->insn_handler = actions[d->handler.action].handler;
+                        int action = d->handler.action;
+
+                        err = run_checkers(checkers, action, origin_insn, asi, h);
+                        if (err == INSN_REJECTED)
+                                return INSN_REJECTED;
+                        asi->insn_handler = actions[action].handler;
                         return INSN_GOOD_NO_SLOT;
                 }
 
                 case DECODE_TYPE_EMULATE: {
+                        int err;
                         struct decode_emulate *d = (struct decode_emulate *)h;
+                        int action = d->handler.action;
+
+                        err = run_checkers(checkers, action, origin_insn, asi, h);
+                        if (err == INSN_REJECTED)
+                                return INSN_REJECTED;
 
                         if (!emulate)
-                                return actions[d->handler.action].decoder(insn,
-                                        asi, h);
+                                return actions[action].decoder(insn, asi, h);
 
-                        asi->insn_handler = actions[d->handler.action].handler;
+                        asi->insn_handler = actions[action].handler;
                         set_emulated_insn(insn, asi, thumb);
                         return INSN_GOOD;
                 }