Subject: [PATCH v14 7/7] ARM: kprobes: enable OPTPROBES for ARM 32

From: [email-masked] (Wang Nan)
Date: Mon, 8 Dec 2014 20:31:40 +0800

On 2014/12/8 20:06, Wang Nan wrote:
> On 2014/12/8 19:50, Jon Medhurst (Tixy) wrote:
>> On Mon, 2014-12-08 at 19:15 +0800, Wang Nan wrote:
>>> On 2014/12/8 19:04, Jon Medhurst (Tixy) wrote:
>>>> On Mon, 2014-12-08 at 14:28 +0800, Wang Nan wrote:
[...]
>>
>> so another CPU could find and delete next before this one has finished
>> doing so. Would the list end up in a consistent state where no loops
>> develop and no probes are missed? I don't know the answer and a full
>> analysis would be complicated, but my gut feeling is that if a cpu can
>> observe the links in the list in an inconsistent state then only bad
>> things can result.
>>
> 
> I see the problem.
> 
> I'm thinking about making core.c and opt-arm.c to share stop_machine() code.
> stop_machine() is required when removing breakpoint, so I'd like to define
> a "remove_breakpoint" function in core.c and make opt-arm.c to call it.
> Do you think it is a good idea?
> 
> 

What I mean is something like this:

diff --git a/arch/arm/probes/kprobes/core.c b/arch/arm/probes/kprobes/core.c
index 3a58db4..efd8ab1 100644
--- a/arch/arm/probes/kprobes/core.c
+++ b/arch/arm/probes/kprobes/core.c
@@ -163,19 +163,31 @@ void __kprobes arch_arm_kprobe(struct kprobe *p)
  * memory. It is also needed to atomically set the two half-words of a 32-bit
  * Thumb breakpoint.
  */
-int __kprobes __arch_disarm_kprobe(void *p)
-{
-	struct kprobe *kp = p;
-	void *addr = (void *)((uintptr_t)kp->addr & ~1);
-
-	__patch_text(addr, kp->opcode);
+struct patch {
+	void *addr;
+	unsigned int insn;
+};

+static int __remove_breakpoint(void *data)
+{
+	struct patch *p = data;
+	__patch_text(p->addr, p->insn);
 	return 0;
 }

+void __kprobes remove_breakpoint(void *addr, unsigned int insn)
+{
+	struct patch p = {
+		.addr = addr,
+		.insn = insn,
+	};
+	stop_machine(__remove_breakpoint, &p, cpu_online_mask);
+}
+
 void __kprobes arch_disarm_kprobe(struct kprobe *p)
 {
-	stop_machine(__arch_disarm_kprobe, p, cpu_online_mask);
+	remove_breakpoint((void *)((uintptr_t)p->addr & ~1),
+			p->opcode);
 }

 void __kprobes arch_remove_kprobe(struct kprobe *p)
diff --git a/arch/arm/probes/kprobes/core.h b/arch/arm/probes/kprobes/core.h
index f88c79f..7b7c334 100644
--- a/arch/arm/probes/kprobes/core.h
+++ b/arch/arm/probes/kprobes/core.h
@@ -30,6 +30,8 @@
 #define KPROBE_THUMB16_BREAKPOINT_INSTRUCTION	0xde18
 #define KPROBE_THUMB32_BREAKPOINT_INSTRUCTION	0xf7f0a018

+extern void remove_breakpoint(void *addr, unsigned int insn);
+
 enum probes_insn __kprobes
 kprobe_decode_ldmstm(kprobe_opcode_t insn, struct arch_probes_insn *asi,
 		const struct decode_header *h);
diff --git a/arch/arm/probes/kprobes/opt-arm.c b/arch/arm/probes/kprobes/opt-arm.c
index afbfeef..a1a1882 100644
--- a/arch/arm/probes/kprobes/opt-arm.c
+++ b/arch/arm/probes/kprobes/opt-arm.c
@@ -28,8 +28,9 @@
 #include <asm/insn.h>
 /* for patch_text */
 #include <asm/patch.h>
-/* for stop_machine */
-#include <linux/stop_machine.h>
+
+#include "core.h"
+
 /*
  * NOTE: the first sub and add instruction will be modified according
  * to the stack cost of the instruction.
@@ -245,13 +246,8 @@ int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *or
 	return 0;
 }

-/*
- * Similar to __arch_disarm_kprobe, operations which removing
- * breakpoints must be wrapped by stop_machine to avoid racing.
- */
-static __kprobes int __arch_optimize_kprobes(void *p)
+void __kprobes arch_optimize_kprobes(struct list_head *oplist)
 {
-	struct list_head *oplist = p;
 	struct optimized_kprobe *op, *tmp;

 	list_for_each_entry_safe(op, tmp, oplist, list) {
@@ -277,16 +273,15 @@ static __kprobes int __arch_optimize_kprobes(void *p)
 			  op->optinsn.copied_insn[0]) & 0xf0000000) |
 			(insn & 0x0fffffff);

-		patch_text(op->kp.addr, insn);
+		/*
+		 * Similar to __arch_disarm_kprobe, operations which
+		 * removing breakpoints must be wrapped by stop_machine
+		 * to avoid racing.
+		 */
+		remove_breakpoint(op->kp.addr, insn);

 		list_del_init(&op->list);
 	}
-	return 0;
-}
-
-void arch_optimize_kprobes(struct list_head *oplist)
-{
-	stop_machine(__arch_optimize_kprobes, oplist, cpu_online_mask);
 }

 void arch_unoptimize_kprobe(struct optimized_kprobe *op)

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