Patch "kprobes/x86: Return correct length in __copy_instruction()" has been added to the 4.0-stable tree

This is a note to let you know that I've just added the patch titled

kprobes/x86: Return correct length in __copy_instruction()

to the 4.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kprobes-x86-return-correct-length-in-__copy_instruction.patch
and it can be found in the queue-4.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Eugene Shatokhin <[email protected]>
Date: Tue, 17 Mar 2015 19:09:18 +0900
Subject: kprobes/x86: Return correct length in __copy_instruction()

From: Eugene Shatokhin <[email protected]>

commit c80e5c0c23ce2282476fdc64c4b5e3d3a40723fd upstream.

On x86-64, __copy_instruction() always returns 0 (error) if the instruction uses %rip-relative addressing. This is because kernel_insn_init() is called the second time for 'insn' instance in such cases and sets all its fields to 0.

Because of this, trying to place a kprobe on such instruction will fail, register_kprobe() will return -EINVAL.

This patch fixes the problem.

---
 arch/x86/kernel/kprobes/core.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

@@ -354,6 +354,7 @@ int __copy_instruction(u8 *dest, u8 *src
 {
 	struct insn insn;
 	kprobe_opcode_t buf[MAX_INSN_SIZE];
+	int length;
 	unsigned long recovered_insn =
 		recover_probed_instruction(buf, (unsigned long)src);
 

@@ -361,16 +362,18 @@ int __copy_instruction(u8 *dest, u8 *src
 		return 0;
 	kernel_insn_init(&insn, (void *)recovered_insn, MAX_INSN_SIZE);
 	insn_get_length(&insn);
+	length = insn.length;
+
 	/* Another subsystem puts a breakpoint, failed to recover */
 	if (insn.opcode.bytes[0] == BREAKPOINT_INSTRUCTION)
 		return 0;
-	memcpy(dest, insn.kaddr, insn.length);
+	memcpy(dest, insn.kaddr, length);
 
 #ifdef CONFIG_X86_64
 	if (insn_rip_relative(&insn)) {
 		s64 newdisp;
 		u8 *disp;
-		kernel_insn_init(&insn, dest, insn.length);
+		kernel_insn_init(&insn, dest, length);
 		insn_get_displacement(&insn);
 		/*
 		 * The copied instruction uses the %rip-relative addressing

@@ -394,7 +397,7 @@ int __copy_instruction(u8 *dest, u8 *src
 		*(s32 *) disp = (s32) newdisp;
 	}
 #endif
-	return insn.length;
+	return length;
 }
 
 static int arch_copy_kprobe(struct kprobe *p)

Patches currently in stable-queue which might be from [email protected] are

queue-4.0/kprobes-x86-return-correct-length-in-__copy_instruction.patch