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Subject[PATCH v18 10/11] ARM: kprobes: check register usage for probed instruction.
Date
This patch utilizes previous introduced checker to check register usage
for probed ARM instruction and saves it in a mask. Futher patch will
use such information to avoid simuation or emulation.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
---
arch/arm/include/asm/probes.h | 12 ++++
arch/arm/probes/decode.c | 7 ++
arch/arm/probes/kprobes/actions-arm.c | 2 +-
arch/arm/probes/kprobes/checkers-arm.c | 124 +++++++++++++++++++++++++++++++++
arch/arm/probes/kprobes/checkers.h | 1 +
5 files changed, 145 insertions(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/probes.h b/arch/arm/include/asm/probes.h
index f0a1ee8..ee04067 100644
--- a/arch/arm/include/asm/probes.h
+++ b/arch/arm/include/asm/probes.h
@@ -41,6 +41,18 @@ struct arch_probes_insn {
probes_insn_singlestep_t *insn_singlestep;
probes_insn_fn_t *insn_fn;
int stack_space;
+
+ /* Use 2 bits for a register. One more bit for extension */
+#define REG_NO_USE (0)
+#define REG_USE (1)
+#define REG_MASK (3)
+#define __register_usage_flag(n, f) ((f) << ((n) * 2))
+#define __register_usage_mask(n) (REG_MASK << ((n) * 2))
+#define __clean_register_flag(m, n) ((m) & (~(__register_usage_mask(n))))
+#define __set_register_flag(m, n, f) (__clean_register_flag(m, n) | __register_usage_flag(n, f))
+#define set_register_nouse(m, n) do {(m) = __set_register_flag(m, n, REG_NO_USE);} while(0)
+#define set_register_use(m, n) do {(m) = __set_register_flag(m, n, REG_USE);} while(0)
+ int register_usage_mask;
};

#endif /* __ASSEMBLY__ */
diff --git a/arch/arm/probes/decode.c b/arch/arm/probes/decode.c
index f9d7c42..d60a1b2 100644
--- a/arch/arm/probes/decode.c
+++ b/arch/arm/probes/decode.c
@@ -435,6 +435,13 @@ probes_decode_insn(probes_opcode_t insn, struct arch_probes_insn *asi,
*/
asi->stack_space = 0;

+ /*
+ * Similay to stack_space, register_usage_mask is filled by
+ * checkers. Its default value is set to ~0, which is 'all
+ * registers are used', to prevent any potential optimization.
+ */
+ asi->register_usage_mask = ~(0UL);
+
if (emulate)
insn = prepare_emulated_insn(insn, asi, thumb);

diff --git a/arch/arm/probes/kprobes/actions-arm.c b/arch/arm/probes/kprobes/actions-arm.c
index 4fedd4c..26e435b 100644
--- a/arch/arm/probes/kprobes/actions-arm.c
+++ b/arch/arm/probes/kprobes/actions-arm.c
@@ -340,4 +340,4 @@ const union decode_action kprobes_arm_actions[NUM_PROBES_ARM_ACTIONS] = {
[PROBES_LDMSTM] = {.decoder = kprobe_decode_ldmstm}
};

-const struct decode_checker *kprobes_arm_checkers[] = {arm_stack_checker, NULL};
+const struct decode_checker *kprobes_arm_checkers[] = {arm_stack_checker, arm_regs_checker, NULL};
diff --git a/arch/arm/probes/kprobes/checkers-arm.c b/arch/arm/probes/kprobes/checkers-arm.c
index f817663..df1d77b 100644
--- a/arch/arm/probes/kprobes/checkers-arm.c
+++ b/arch/arm/probes/kprobes/checkers-arm.c
@@ -97,3 +97,127 @@ const struct decode_checker arm_stack_checker[NUM_PROBES_ARM_ACTIONS] = {
[PROBES_STORE] = {.checker = arm_check_stack},
[PROBES_LDMSTM] = {.checker = arm_check_stack},
};
+
+static enum probes_insn __kprobes arm_check_regs_nouse(probes_opcode_t insn,
+ struct arch_probes_insn *asi,
+ const struct decode_header *h)
+{
+ asi->register_usage_mask = 0;
+ return INSN_GOOD;
+}
+
+static void __arm_check_regs(probes_opcode_t insn,
+ const struct decode_header *h,
+ int *quintuple)
+{
+ int i;
+ u32 regs = h->type_regs.bits >> DECODE_TYPE_BITS;
+ probes_opcode_t mask, shifted;
+
+ memset(quintuple, 0xff, sizeof(int) * 5);
+ for (i = 0, shifted = insn, mask = 0xf; regs != 0;
+ regs >>= 4, mask <<= 4, shifted >>= 4, i++)
+ if (regs & 0xf)
+ quintuple[i] = shifted & 0xf;
+}
+
+static enum probes_insn arm_check_regs_normal(probes_opcode_t insn,
+ struct arch_probes_insn *asi,
+ const struct decode_header *h)
+{
+ int quintuple[5], i;
+ asi->register_usage_mask = 0;
+ __arm_check_regs(insn, h, quintuple);
+ for (i = 0; i < 5; i++) {
+ int r = quintuple[i];
+ if (r < 0)
+ continue;
+ set_register_use(asi->register_usage_mask, r);
+ }
+
+ return INSN_GOOD;
+}
+
+static enum probes_insn arm_check_regs_ldmstm(probes_opcode_t insn,
+ struct arch_probes_insn *asi,
+ const struct decode_header *h)
+{
+ unsigned int reglist = insn & 0xffff;
+ unsigned int rn = (insn >> 16) & 0xf;
+ int i;
+
+ set_register_use(asi->register_usage_mask, rn);
+ for (i = 0; reglist > 0; i++, reglist >>= 1)
+ if (reglist & 1)
+ set_register_use(asi->register_usage_mask, i);
+ return INSN_GOOD;
+}
+
+static enum probes_insn arm_check_regs_mov_ip_sp(probes_opcode_t insn,
+ struct arch_probes_insn *asi,
+ const struct decode_header *h)
+{
+ /* should be 'mov ip, sp' */
+ set_register_use(asi->register_usage_mask, 12);
+ set_register_use(asi->register_usage_mask, 13);
+ return INSN_GOOD;
+}
+
+/*
+ * | Rn |Rt/d| | Rm |
+ * LDRD (register) cccc 000x x0x0 xxxx xxxx xxxx 1101 xxxx
+ * STRD (register) cccc 000x x0x0 xxxx xxxx xxxx 1111 xxxx
+ * | Rn |Rt/d| |imm4L|
+ * LDRD (immediate) cccc 000x x1x0 xxxx xxxx xxxx 1101 xxxx
+ * STRD (immediate) cccc 000x x1x0 xxxx xxxx xxxx 1111 xxxx
+ *
+ * Such instructions access Rt/d and its next register, so different
+ * from others, a specific checker is required for Rt/d and Rt2/d2.
+ */
+static enum probes_insn arm_check_regs_ldrdstrd(probes_opcode_t insn,
+ struct arch_probes_insn *asi,
+ const struct decode_header *h)
+{
+ int quintuple[5], rn, rdt, rm;
+ asi->register_usage_mask = 0;
+ __arm_check_regs(insn, h, quintuple);
+
+ rn = quintuple[4];
+ rdt = quintuple[3];
+ rm = quintuple[0];
+ set_register_use(asi->register_usage_mask, rn);
+ set_register_use(asi->register_usage_mask, rdt);
+ set_register_use(asi->register_usage_mask, rdt + 1);
+ if (rm >= 0)
+ set_register_use(asi->register_usage_mask, rm);
+
+ return INSN_GOOD;
+}
+
+
+const struct decode_checker arm_regs_checker[NUM_PROBES_ARM_ACTIONS] = {
+ [PROBES_EMULATE_NONE] = {.checker = arm_check_regs_nouse},
+ [PROBES_SIMULATE_NOP] = {.checker = arm_check_regs_nouse},
+ [PROBES_MRS] = {.checker = arm_check_regs_normal},
+ [PROBES_SATURATING_ARITHMETIC] = {.checker = arm_check_regs_normal},
+ [PROBES_MUL1] = {.checker = arm_check_regs_normal},
+ [PROBES_MUL2] = {.checker = arm_check_regs_normal},
+ [PROBES_MUL_ADD_LONG] = {.checker = arm_check_regs_normal},
+ [PROBES_MUL_ADD] = {.checker = arm_check_regs_normal},
+ [PROBES_LOAD] = {.checker = arm_check_regs_normal},
+ [PROBES_LOAD_EXTRA] = {.checker = arm_check_regs_normal},
+ [PROBES_STORE] = {.checker = arm_check_regs_normal},
+ [PROBES_STORE_EXTRA] = {.checker = arm_check_regs_normal},
+ [PROBES_DATA_PROCESSING_REG] = {.checker = arm_check_regs_normal},
+ [PROBES_DATA_PROCESSING_IMM] = {.checker = arm_check_regs_normal},
+ [PROBES_SATURATE] = {.checker = arm_check_regs_normal},
+ [PROBES_REV] = {.checker = arm_check_regs_normal},
+ [PROBES_MMI] = {.checker = arm_check_regs_normal},
+ [PROBES_PACK] = {.checker = arm_check_regs_normal},
+ [PROBES_EXTEND] = {.checker = arm_check_regs_normal},
+ [PROBES_EXTEND_ADD] = {.checker = arm_check_regs_normal},
+ [PROBES_BITFIELD] = {.checker = arm_check_regs_normal},
+ [PROBES_LDMSTM] = {.checker = arm_check_regs_ldmstm},
+ [PROBES_MOV_IP_SP] = {.checker = arm_check_regs_mov_ip_sp},
+ [PROBES_LDRSTRD] = {.checker = arm_check_regs_ldrdstrd},
+};
diff --git a/arch/arm/probes/kprobes/checkers.h b/arch/arm/probes/kprobes/checkers.h
index bddfa0e..cf6c9e7 100644
--- a/arch/arm/probes/kprobes/checkers.h
+++ b/arch/arm/probes/kprobes/checkers.h
@@ -47,6 +47,7 @@ extern const union decode_action stack_check_actions[];

#ifndef CONFIG_THUMB2_KERNEL
extern const struct decode_checker arm_stack_checker[];
+extern const struct decode_checker arm_regs_checker[];
#else
#endif
extern const struct decode_checker t32_stack_checker[];
--
1.8.4


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