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>

11 files changed, 95 insertions, 20 deletions

diff --git a/arch/arm/probes/decode-arm.c b/arch/arm/probes/decode-arm.c
index 04114f74a2d2..f72c33a2dcfb 100644
--- a/arch/arm/probes/decode-arm.c
+++ b/arch/arm/probes/decode-arm.c
@@ -726,10 +726,11 @@ static void __kprobes arm_singlestep(probes_opcode_t insn,
  */
 enum probes_insn __kprobes
 arm_probes_decode_insn(probes_opcode_t insn, struct arch_probes_insn *asi,
-                       bool emulate, const union decode_action *actions)
+                       bool emulate, const union decode_action *actions,
+                       const struct decode_checker *checkers[])
 {
         asi->insn_singlestep = arm_singlestep;
         asi->insn_check_cc = probes_condition_checks[insn>>28];
         return probes_decode_insn(insn, asi, probes_decode_arm_table, false,
-                                  emulate, actions);
+                                  emulate, actions, checkers);
 }
diff --git a/arch/arm/probes/decode-arm.h b/arch/arm/probes/decode-arm.h
index cb0b26331930..b3b80f6d414b 100644
--- a/arch/arm/probes/decode-arm.h
+++ b/arch/arm/probes/decode-arm.h
@@ -68,6 +68,7 @@ extern const union decode_item probes_decode_arm_table[];
 
 enum probes_insn arm_probes_decode_insn(probes_opcode_t,
                 struct arch_probes_insn *, bool emulate,
-                const union decode_action *actions);
+                const union decode_action *actions,
+                const struct decode_checker *checkers[]);
 
 #endif
diff --git a/arch/arm/probes/decode-thumb.c b/arch/arm/probes/decode-thumb.c
index 2f0453a895dc..985e7dd4cac6 100644
--- a/arch/arm/probes/decode-thumb.c
+++ b/arch/arm/probes/decode-thumb.c
@@ -863,20 +863,22 @@ static void __kprobes thumb32_singlestep(probes_opcode_t opcode,
 
 enum probes_insn __kprobes
 thumb16_probes_decode_insn(probes_opcode_t insn, struct arch_probes_insn *asi,
-                           bool emulate, const union decode_action *actions)
+                           bool emulate, const union decode_action *actions,
+                           const struct decode_checker *checkers[])
 {
         asi->insn_singlestep = thumb16_singlestep;
         asi->insn_check_cc = thumb_check_cc;
         return probes_decode_insn(insn, asi, probes_decode_thumb16_table, true,
-                                  emulate, actions);
+                                  emulate, actions, checkers);
 }
 
 enum probes_insn __kprobes
 thumb32_probes_decode_insn(probes_opcode_t insn, struct arch_probes_insn *asi,
-                           bool emulate, const union decode_action *actions)
+                           bool emulate, const union decode_action *actions,
+                           const struct decode_checker *checkers[])
 {
         asi->insn_singlestep = thumb32_singlestep;
         asi->insn_check_cc = thumb_check_cc;
         return probes_decode_insn(insn, asi, probes_decode_thumb32_table, true,
-                                  emulate, actions);
+                                  emulate, actions, checkers);
 }
diff --git a/arch/arm/probes/decode-thumb.h b/arch/arm/probes/decode-thumb.h
index 039013c7131d..8457add0a2d8 100644
--- a/arch/arm/probes/decode-thumb.h
+++ b/arch/arm/probes/decode-thumb.h
@@ -91,9 +91,11 @@ extern const union decode_item probes_decode_thumb16_table[];
 
 enum probes_insn __kprobes
 thumb16_probes_decode_insn(probes_opcode_t insn, struct arch_probes_insn *asi,
-                bool emulate, const union decode_action *actions);
+                bool emulate, const union decode_action *actions,
+                const struct decode_checker *checkers[]);
 enum probes_insn __kprobes
 thumb32_probes_decode_insn(probes_opcode_t insn, struct arch_probes_insn *asi,
-                bool emulate, const union decode_action *actions);
+                bool emulate, const union decode_action *actions,
+                const struct decode_checker *checkers[]);
 
 #endif
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;
                 }
diff --git a/arch/arm/probes/decode.h b/arch/arm/probes/decode.h
index 1d0b53169080..f9b08ba7fe73 100644
--- a/arch/arm/probes/decode.h
+++ b/arch/arm/probes/decode.h
@@ -314,6 +314,14 @@ union decode_action {
         probes_custom_decode_t  *decoder;
 };
 
+typedef enum probes_insn (probes_check_t)(probes_opcode_t,
+                                           struct arch_probes_insn *,
+                                           const struct decode_header *);
+
+struct decode_checker {
+        probes_check_t  *checker;
+};
+
 #define DECODE_END                      \
         {.bits = DECODE_TYPE_END}
 
@@ -402,6 +410,7 @@ probes_insn_handler_t probes_emulate_none;
 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);
+                const union decode_action *actions,
+                const struct decode_checker **checkers);
 
 #endif
diff --git a/arch/arm/probes/kprobes/actions-arm.c b/arch/arm/probes/kprobes/actions-arm.c
index 2206f2d80c76..fbd93a9ada75 100644
--- a/arch/arm/probes/kprobes/actions-arm.c
+++ b/arch/arm/probes/kprobes/actions-arm.c
@@ -339,3 +339,5 @@ const union decode_action kprobes_arm_actions[NUM_PROBES_ARM_ACTIONS] = {
         [PROBES_BRANCH] = {.handler = simulate_bbl},
         [PROBES_LDMSTM] = {.decoder = kprobe_decode_ldmstm}
 };
+
+const struct decode_checker *kprobes_arm_checkers[] = {NULL};
diff --git a/arch/arm/probes/kprobes/actions-thumb.c b/arch/arm/probes/kprobes/actions-thumb.c
index 6c4e60b62826..2796121fe90e 100644
--- a/arch/arm/probes/kprobes/actions-thumb.c
+++ b/arch/arm/probes/kprobes/actions-thumb.c
@@ -664,3 +664,6 @@ const union decode_action kprobes_t32_actions[NUM_PROBES_T32_ACTIONS] = {
         [PROBES_T32_MUL_ADD_LONG] = {
                 .handler = t32_emulate_rdlo12rdhi8rn16rm0_noflags},
 };
+
+const struct decode_checker *kprobes_t32_checkers[] = {NULL};
+const struct decode_checker *kprobes_t16_checkers[] = {NULL};
diff --git a/arch/arm/probes/kprobes/core.c b/arch/arm/probes/kprobes/core.c
index 701f49d74c35..74f3dc3ac212 100644
--- a/arch/arm/probes/kprobes/core.c
+++ b/arch/arm/probes/kprobes/core.c
@@ -61,6 +61,7 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
         kprobe_decode_insn_t *decode_insn;
         const union decode_action *actions;
         int is;
+        const struct decode_checker **checkers;
 
         if (in_exception_text(addr))
                 return -EINVAL;
@@ -74,9 +75,11 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
                 insn = __opcode_thumb32_compose(insn, inst2);
                 decode_insn = thumb32_probes_decode_insn;
                 actions = kprobes_t32_actions;
+                checkers = kprobes_t32_checkers;
         } else {
                 decode_insn = thumb16_probes_decode_insn;
                 actions = kprobes_t16_actions;
+                checkers = kprobes_t16_checkers;
         }
 #else /* !CONFIG_THUMB2_KERNEL */
         thumb = false;
@@ -85,12 +88,13 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
         insn = __mem_to_opcode_arm(*p->addr);
         decode_insn = arm_probes_decode_insn;
         actions = kprobes_arm_actions;
+        checkers = kprobes_arm_checkers;
 #endif
 
         p->opcode = insn;
         p->ainsn.insn = tmp_insn;
 
-        switch ((*decode_insn)(insn, &p->ainsn, true, actions)) {
+        switch ((*decode_insn)(insn, &p->ainsn, true, actions, checkers)) {
         case INSN_REJECTED:     /* not supported */
                 return -EINVAL;
 
diff --git a/arch/arm/probes/kprobes/core.h b/arch/arm/probes/kprobes/core.h
index 2e1e5a3d9155..f88c79fe632a 100644
--- a/arch/arm/probes/kprobes/core.h
+++ b/arch/arm/probes/kprobes/core.h
@@ -37,16 +37,19 @@ kprobe_decode_ldmstm(kprobe_opcode_t insn, struct arch_probes_insn *asi,
 typedef enum probes_insn (kprobe_decode_insn_t)(probes_opcode_t,
                                                 struct arch_probes_insn *,
                                                 bool,
-                                                const union decode_action *);
+                                                const union decode_action *,
+                                                const struct decode_checker *[*]);
 
 #ifdef CONFIG_THUMB2_KERNEL
 
 extern const union decode_action kprobes_t32_actions[];
 extern const union decode_action kprobes_t16_actions[];
-
+extern const struct decode_checker *kprobes_t32_checkers[];
+extern const struct decode_checker *kprobes_t16_checkers[];
 #else /* !CONFIG_THUMB2_KERNEL */
 
 extern const union decode_action kprobes_arm_actions[];
+extern const struct decode_checker *kprobes_arm_checkers[];
 
 #endif
 
diff --git a/arch/arm/probes/uprobes/core.c b/arch/arm/probes/uprobes/core.c
index b2954f6d3abe..d1329f1ba4e4 100644
--- a/arch/arm/probes/uprobes/core.c
+++ b/arch/arm/probes/uprobes/core.c
@@ -88,7 +88,7 @@ int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct mm_struct *mm,
         auprobe->ixol[1] = __opcode_to_mem_arm(UPROBE_SS_ARM_INSN);
 
         ret = arm_probes_decode_insn(insn, &auprobe->asi, false,
-                                     uprobes_probes_actions);
+                                     uprobes_probes_actions, NULL);
         switch (ret) {
         case INSN_REJECTED:
                 return -EINVAL;