[PATCH v2 3/3] ARM: kprobes: disallow probing stack consuming instructions

Wang Nan
2014-11-18T06:23:22Z

This patch prohibit probing instructions for which the stack
requirement are unable to be determined statically. Some test cases
are found not work again after the modification, this patch also
removes them.

v1 -> v2:
- Use MAX_STACK_SIZE macro instead of hard coded stack size.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
---
arch/arm/include/asm/kprobes.h | 1 -
arch/arm/include/asm/probes.h | 12 ++++++++++++
arch/arm/kernel/entry-armv.S | 3 ++-
arch/arm/kernel/kprobes-test-arm.c | 16 ++++++++++------
arch/arm/kernel/kprobes.c | 9 +++++++++
5 files changed, 33 insertions(+), 8 deletions(-)

diff --git a/arch/arm/include/asm/kprobes.h b/arch/arm/include/asm/kprobes.h
index 49fa0df..56f9ac6 100644
--- a/arch/arm/include/asm/kprobes.h
+++ b/arch/arm/include/asm/kprobes.h
@@ -22,7 +22,6 @@

#define __ARCH_WANT_KPROBES_INSN_SLOT
#define MAX_INSN_SIZE 2
-#define MAX_STACK_SIZE 64 /* 32 would probably be OK */

#define flush_insn_slot(p) do { } while (0)
#define kretprobe_blacklist_size 0
diff --git a/arch/arm/include/asm/probes.h b/arch/arm/include/asm/probes.h
index ccf9af3..f0a1ee8 100644
--- a/arch/arm/include/asm/probes.h
+++ b/arch/arm/include/asm/probes.h
@@ -19,6 +19,8 @@
#ifndef _ASM_PROBES_H
#define _ASM_PROBES_H

+#ifndef __ASSEMBLY__
+
typedef u32 probes_opcode_t;

struct arch_probes_insn;
@@ -41,4 +43,14 @@ struct arch_probes_insn {
int stack_space;
};

+#endif /* __ASSEMBLY__ */
+
+/*
+ * We assume one instruction can consume at most 64 bytes stack, which is
+ * 'push {r0-r15}'. Instructions consume more or unknown stack space like
+ * 'str r0, [sp, #-80]' and 'str r0, [sp, r1]' should be prohibit to probe.
+ * Both kprobe and jprobe use this macro.
+ */
+#define MAX_STACK_SIZE 64
+
#endif
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 2f5555d..672b219 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -31,6 +31,7 @@

#include "entry-header.S"
#include <asm/entry-macro-multi.S>
+#include <asm/probes.h>

/*
* Interrupt handling.
@@ -249,7 +250,7 @@ __und_svc:
@ If a kprobe is about to simulate a "stmdb sp..." instruction,
@ it obviously needs free stack space which then will belong to
@ the saved context.
- svc_entry 64
+ svc_entry MAX_STACK_SIZE
#else
svc_entry
#endif
diff --git a/arch/arm/kernel/kprobes-test-arm.c b/arch/arm/kernel/kprobes-test-arm.c
index cb14242..d8ad5bb 100644
--- a/arch/arm/kernel/kprobes-test-arm.c
+++ b/arch/arm/kernel/kprobes-test-arm.c
@@ -476,7 +476,8 @@ void kprobe_arm_test_cases(void)
TEST_GROUP("Extra load/store instructions")

TEST_RPR( "strh r",0, VAL1,", [r",1, 48,", -r",2, 24,"]")
- TEST_RPR( "streqh r",14,VAL2,", [r",13,0, ", r",12, 48,"]")
+ TEST_RPR( "streqh r",14,VAL2,", [r",11,0, ", r",12, 48,"]")
+ TEST_UNSUPPORTED( "streqh r14, [r13, r12]")
TEST_RPR( "strh r",1, VAL1,", [r",2, 24,", r",3, 48,"]!")
TEST_RPR( "strneh r",12,VAL2,", [r",11,48,", -r",10,24,"]!")
TEST_RPR( "strh r",2, VAL1,", [r",3, 24,"], r",4, 48,"")
@@ -565,7 +566,8 @@ void kprobe_arm_test_cases(void)

#if __LINUX_ARM_ARCH__ >= 5
TEST_RPR( "strd r",0, VAL1,", [r",1, 48,", -r",2,24,"]")
- TEST_RPR( "strccd r",8, VAL2,", [r",13,0, ", r",12,48,"]")
+ TEST_RPR( "strccd r",8, VAL2,", [r",11,0, ", r",12,48,"]")
+ TEST_UNSUPPORTED( "strccd r8, [r13, r12]")
TEST_RPR( "strd r",4, VAL1,", [r",2, 24,", r",3, 48,"]!")
TEST_RPR( "strcsd r",12,VAL2,", [r",11,48,", -r",10,24,"]!")
TEST_RPR( "strd r",2, VAL1,", [r",5, 24,"], r",4,48,"")
@@ -638,13 +640,15 @@ void kprobe_arm_test_cases(void)
TEST_RP( "str"byte" r",2, VAL1,", [r",3, 24,"], #48") \
TEST_RP( "str"byte" r",10,VAL2,", [r",9, 64,"], #-48") \
TEST_RPR("str"byte" r",0, VAL1,", [r",1, 48,", -r",2, 24,"]") \
- TEST_RPR("str"byte" r",14,VAL2,", [r",13,0, ", r",12, 48,"]") \
+ TEST_RPR("str"byte" r",14,VAL2,", [r",11,0, ", r",12, 48,"]") \
+ TEST_UNSUPPORTED("str"byte" r14, [r13, r12]") \
TEST_RPR("str"byte" r",1, VAL1,", [r",2, 24,", r",3, 48,"]!") \
TEST_RPR("str"byte" r",12,VAL2,", [r",11,48,", -r",10,24,"]!") \
TEST_RPR("str"byte" r",2, VAL1,", [r",3, 24,"], r",4, 48,"") \
TEST_RPR("str"byte" r",10,VAL2,", [r",9, 48,"], -r",11,24,"") \
TEST_RPR("str"byte" r",0, VAL1,", [r",1, 24,", r",2, 32,", asl #1]")\
- TEST_RPR("str"byte" r",14,VAL2,", [r",13,0, ", r",12, 32,", lsr #2]")\
+ TEST_RPR("str"byte" r",14,VAL2,", [r",11,0, ", r",12, 32,", lsr #2]")\
+ TEST_UNSUPPORTED("str"byte" r14, [r13, r12, lsr #2]")\
TEST_RPR("str"byte" r",1, VAL1,", [r",2, 24,", r",3, 32,", asr #3]!")\
TEST_RPR("str"byte" r",12,VAL2,", [r",11,24,", r",10, 4,", ror #31]!")\
TEST_P( "ldr"byte" r0, [r",0, 24,", #-2]") \
@@ -668,12 +672,12 @@ void kprobe_arm_test_cases(void)

LOAD_STORE("")
TEST_P( "str pc, [r",0,0,", #15*4]")
- TEST_R( "str pc, [sp, r",2,15*4,"]")
+ TEST_UNSUPPORTED( "str pc, [sp, r2]")
TEST_BF( "ldr pc, [sp, #15*4]")
TEST_BF_R("ldr pc, [sp, r",2,15*4,"]")

TEST_P( "str sp, [r",0,0,", #13*4]")
- TEST_R( "str sp, [sp, r",2,13*4,"]")
+ TEST_UNSUPPORTED( "str sp, [sp, r2]")
TEST_BF( "ldr sp, [sp, #13*4]")
TEST_BF_R("ldr sp, [sp, r",2,13*4,"]")

diff --git a/arch/arm/kernel/kprobes.c b/arch/arm/kernel/kprobes.c
index d7bee4b..30498436 100644
--- a/arch/arm/kernel/kprobes.c
+++ b/arch/arm/kernel/kprobes.c
@@ -115,6 +115,15 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
break;
}

+ /*
+ * Never instrument insn like 'str r0, [sp, +/-r1]'. Also, insn likes
+ * 'str r0, [sp, #-68]' should also be prohibited.
+ * See __und_svc.
+ */
+ if ((p->ainsn.stack_space < 0) ||
+ (p->ainsn.stack_space > MAX_STACK_SIZE))
+ return -EINVAL;
+
return 0;
}

--
1.8.4