[PATCH v5 1/3] ARM: probes: check stack operation when decoding

Wang Nan wangnan0 at huawei.com
Wed Aug 27 06:02:30 PDT 2014


This patch improves arm instruction decoder, allows it check whether an
instruction is a stack store operation. This information is important
for kprobe optimization.

For normal str instruction, this patch add a series of _SP_STACK
register indicator in the decoder to test the base and offset register
in ldr <Rt>, [<Rn>, <Rm>] against sp.

For stm instruction, it check sp register in instruction specific
decoder.

Signed-off-by: Wang Nan <wangnan0 at huawei.com>
Cc: Russell King <linux at arm.linux.org.uk>
Cc: "David A. Long" <dave.long at linaro.org> 
Cc: Jon Medhurst <tixy at linaro.org>
Cc: Taras Kondratiuk <taras.kondratiuk at linaro.org>
Cc: Ben Dooks <ben.dooks at codethink.co.uk>
Cc: Ananth N Mavinakayanahalli <ananth at in.ibm.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy at intel.com>
Cc: "David S. Miller" <davem at davemloft.net>
Cc: Masami Hiramatsu <masami.hiramatsu.pt at hitachi.com>
Cc: Will Deacon <will.deacon at arm.com>

---
 arch/arm/include/asm/probes.h    |  1 +
 arch/arm/kernel/kprobes-common.c |  4 ++++
 arch/arm/kernel/probes-arm.c     |  4 ++--
 arch/arm/kernel/probes-thumb.c   |  6 +++---
 arch/arm/kernel/probes.c         | 20 ++++++++++++++++++--
 arch/arm/kernel/probes.h         |  6 ++++++
 6 files changed, 34 insertions(+), 7 deletions(-)

diff --git a/arch/arm/include/asm/probes.h b/arch/arm/include/asm/probes.h
index 806cfe6..3f6912c 100644
--- a/arch/arm/include/asm/probes.h
+++ b/arch/arm/include/asm/probes.h
@@ -38,6 +38,7 @@ struct arch_probes_insn {
 	probes_check_cc			*insn_check_cc;
 	probes_insn_singlestep_t	*insn_singlestep;
 	probes_insn_fn_t		*insn_fn;
+	bool				is_stack_operation;
 };
 
 #endif
diff --git a/arch/arm/kernel/kprobes-common.c b/arch/arm/kernel/kprobes-common.c
index 0bf5d64..4e8b918 100644
--- a/arch/arm/kernel/kprobes-common.c
+++ b/arch/arm/kernel/kprobes-common.c
@@ -133,6 +133,10 @@ kprobe_decode_ldmstm(probes_opcode_t insn, struct arch_probes_insn *asi,
 	int is_ldm = insn & 0x100000;
 	int rn = (insn >> 16) & 0xf;
 
+	/* whether this is a push instruction? */
+	if ((rn == 0xd) && (!is_ldm))
+		asi->is_stack_operation = true;
+
 	if (rn <= 12 && (reglist & 0xe000) == 0) {
 		/* Instruction only uses registers in the range R0..R12 */
 		handler = emulate_generic_r0_12_noflags;
diff --git a/arch/arm/kernel/probes-arm.c b/arch/arm/kernel/probes-arm.c
index 8eaef81..5c187ba 100644
--- a/arch/arm/kernel/probes-arm.c
+++ b/arch/arm/kernel/probes-arm.c
@@ -577,7 +577,7 @@ static const union decode_item arm_cccc_01xx_table[] = {
 	/* STR (immediate)	cccc 010x x0x0 xxxx xxxx xxxx xxxx xxxx */
 	/* STRB (immediate)	cccc 010x x1x0 xxxx xxxx xxxx xxxx xxxx */
 	DECODE_EMULATEX	(0x0e100000, 0x04000000, PROBES_STORE,
-						 REGS(NOPCWB, ANY, 0, 0, 0)),
+						 REGS(NOPCWB_SP_STACK, ANY, 0, 0, 0)),
 
 	/* LDR (immediate)	cccc 010x x0x1 xxxx xxxx xxxx xxxx xxxx */
 	/* LDRB (immediate)	cccc 010x x1x1 xxxx xxxx xxxx xxxx xxxx */
@@ -587,7 +587,7 @@ static const union decode_item arm_cccc_01xx_table[] = {
 	/* STR (register)	cccc 011x x0x0 xxxx xxxx xxxx xxxx xxxx */
 	/* STRB (register)	cccc 011x x1x0 xxxx xxxx xxxx xxxx xxxx */
 	DECODE_EMULATEX	(0x0e100000, 0x06000000, PROBES_STORE,
-						 REGS(NOPCWB, ANY, 0, 0, NOPC)),
+						 REGS(NOPCWB_SP_STACK, ANY, 0, 0, NOPC_SP_STACK)),
 
 	/* LDR (register)	cccc 011x x0x1 xxxx xxxx xxxx xxxx xxxx */
 	/* LDRB (register)	cccc 011x x1x1 xxxx xxxx xxxx xxxx xxxx */
diff --git a/arch/arm/kernel/probes-thumb.c b/arch/arm/kernel/probes-thumb.c
index 4131351..d0d30d8 100644
--- a/arch/arm/kernel/probes-thumb.c
+++ b/arch/arm/kernel/probes-thumb.c
@@ -54,7 +54,7 @@ static const union decode_item t32_table_1110_100x_x1xx[] = {
 	/* STRD (immediate)	1110 1001 x1x0 xxxx xxxx xxxx xxxx xxxx */
 	/* LDRD (immediate)	1110 1001 x1x1 xxxx xxxx xxxx xxxx xxxx */
 	DECODE_EMULATEX	(0xff400000, 0xe9400000, PROBES_T32_LDRDSTRD,
-						 REGS(NOPCWB, NOSPPC, NOSPPC, 0, 0)),
+						 REGS(NOPCWB_SP_STACK, NOSPPC, NOSPPC, 0, 0)),
 
 	/* TBB			1110 1000 1101 xxxx xxxx xxxx 0000 xxxx */
 	/* TBH			1110 1000 1101 xxxx xxxx xxxx 0001 xxxx */
@@ -345,12 +345,12 @@ static const union decode_item t32_table_1111_100x[] = {
 	/* STR (immediate)	1111 1000 1100 xxxx xxxx xxxx xxxx xxxx */
 	/* LDR (immediate)	1111 1000 1101 xxxx xxxx xxxx xxxx xxxx */
 	DECODE_EMULATEX	(0xffe00000, 0xf8c00000, PROBES_T32_LDRSTR,
-						 REGS(NOPCX, ANY, 0, 0, 0)),
+						 REGS(NOPCX_SP_STACK, ANY, 0, 0, 0)),
 
 	/* STR (register)	1111 1000 0100 xxxx xxxx 0000 00xx xxxx */
 	/* LDR (register)	1111 1000 0101 xxxx xxxx 0000 00xx xxxx */
 	DECODE_EMULATEX	(0xffe00fc0, 0xf8400000, PROBES_T32_LDRSTR,
-						 REGS(NOPCX, ANY, 0, 0, NOSPPC)),
+						 REGS(NOPCX_SP_STACK, ANY, 0, 0, NOSPPC)),
 
 	/* LDRB (literal)	1111 1000 x001 1111 xxxx xxxx xxxx xxxx */
 	/* LDRSB (literal)	1111 1001 x001 1111 xxxx xxxx xxxx xxxx */
diff --git a/arch/arm/kernel/probes.c b/arch/arm/kernel/probes.c
index 1c77b8d..f811cac 100644
--- a/arch/arm/kernel/probes.c
+++ b/arch/arm/kernel/probes.c
@@ -258,7 +258,9 @@ set_emulated_insn(probes_opcode_t insn, struct arch_probes_insn *asi,
  * non-zero value, the corresponding nibble in pinsn is validated and modified
  * according to the type.
  */
-static bool __kprobes decode_regs(probes_opcode_t *pinsn, u32 regs, bool modify)
+static bool __kprobes decode_regs(probes_opcode_t *pinsn,
+		struct arch_probes_insn *asi,
+		u32 regs, bool modify)
 {
 	probes_opcode_t insn = *pinsn;
 	probes_opcode_t mask = 0xf; /* Start at least significant nibble */
@@ -307,11 +309,14 @@ static bool __kprobes decode_regs(probes_opcode_t *pinsn, u32 regs, bool modify)
 				goto reject;
 			break;
 
+		case REG_TYPE_NOPCWB_SP_STACK:
 		case REG_TYPE_NOPCWB:
 			if (!is_writeback(insn))
 				break; /* No writeback, so any register is OK */
 			/* fall through... */
+		case REG_TYPE_NOPC_SP_STACK:
 		case REG_TYPE_NOPC:
+		case REG_TYPE_NOPCX_SP_STACK:
 		case REG_TYPE_NOPCX:
 			/* Reject PC (R15) */
 			if (((insn ^ 0xffffffff) & mask) == 0)
@@ -319,6 +324,15 @@ static bool __kprobes decode_regs(probes_opcode_t *pinsn, u32 regs, bool modify)
 			break;
 		}
 
+		/* check stack operation */
+		switch (regs & 0xf) {
+			case REG_TYPE_NOPCWB_SP_STACK:
+			case REG_TYPE_NOPC_SP_STACK:
+			case REG_TYPE_NOPCX_SP_STACK:
+				if (((insn ^ 0xdddddddd) & mask) == 0)
+					asi->is_stack_operation = true;
+		}
+
 		/* Replace value of nibble with new register number... */
 		insn &= ~mask;
 		insn |= new_bits & mask;
@@ -394,6 +408,8 @@ probes_decode_insn(probes_opcode_t insn, struct arch_probes_insn *asi,
 	const struct decode_header *next;
 	bool matched = false;
 
+	asi->is_stack_operation = false;
+
 	if (emulate)
 		insn = prepare_emulated_insn(insn, asi, thumb);
 
@@ -410,7 +426,7 @@ probes_decode_insn(probes_opcode_t insn, struct arch_probes_insn *asi,
 		if (!matched && (insn & h->mask.bits) != h->value.bits)
 			continue;
 
-		if (!decode_regs(&insn, regs, emulate))
+		if (!decode_regs(&insn, asi, regs, emulate))
 			return INSN_REJECTED;
 
 		switch (type) {
diff --git a/arch/arm/kernel/probes.h b/arch/arm/kernel/probes.h
index dba9f24..568fd01 100644
--- a/arch/arm/kernel/probes.h
+++ b/arch/arm/kernel/probes.h
@@ -278,13 +278,19 @@ enum decode_reg_type {
 	REG_TYPE_NOSP,	   /* Register must not be SP */
 	REG_TYPE_NOSPPC,   /* Register must not be SP or PC */
 	REG_TYPE_NOPC,	   /* Register must not be PC */
+	REG_TYPE_NOPC_SP_STACK,	   /* REG_TYPE_NOPC and if this reg is sp
+				      then this is a stack operation */
 	REG_TYPE_NOPCWB,   /* No PC if load/store write-back flag also set */
+	REG_TYPE_NOPCWB_SP_STACK,   /* REG_TYPE_NOPCWB and, if this reg is sp
+				       then this is a stack operation */
 
 	/* The following types are used when the encoding for PC indicates
 	 * another instruction form. This distiction only matters for test
 	 * case coverage checks.
 	 */
 	REG_TYPE_NOPCX,	   /* Register must not be PC */
+	REG_TYPE_NOPCX_SP_STACK,	   /* REG_TYPE_NOPCX and if this reg is sp
+					      then this is a stack operation */
 	REG_TYPE_NOSPPCX,  /* Register must not be SP or PC */
 
 	/* Alias to allow '0' arg to be used in REGS macro. */
-- 
1.8.4




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