[PATCH v6 5/7] ARM: kprobes: disallow probing stack consuming instructions

From: Wang Nan
Date: Wed Oct 22 2014 - 07:35:01 EST


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.

Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
---
arch/arm/kernel/kprobes-test-arm.c | 16 ++++++++++------
arch/arm/kernel/kprobes.c | 8 ++++++++
2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/arch/arm/kernel/kprobes-test-arm.c b/arch/arm/kernel/kprobes-test-arm.c
index 264c064..59f9b25 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,"")
@@ -639,13 +641,15 @@ 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]") \
@@ -669,12 +673,12 @@ 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 028159c..afbb3e5 100644
--- a/arch/arm/kernel/kprobes.c
+++ b/arch/arm/kernel/kprobes.c
@@ -111,6 +111,14 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
break;
}

+ /*
+ * Unable to instrument insn like 'str r0, [sp, +/-r1]'.
+ * __und_svc protects 64 bytes stack, so instrumenting insn
+ * likes 'str r0, [sp, #-68]' should be prohibited.
+ */
+ if ((p->ainsn.stack_space < 0) || (p->ainsn.stack_space > 64))
+ return -EINVAL;
+
return 0;
}

--
1.8.4

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