[PATCH] Kprobes: Incorrect handling of probes on ret/lret instruction

[Prasanna S Panchamukhi]

Hi,

Kprobes could not handle the insertion of a probe on the ret/lret instruction
and used to oops after single stepping since kprobes was modifying eip/rip 
incorrectly. Adjustment of eip/rip is not required after single stepping in 
case of ret/lret instruction, because eip/rip points to the correct location 
after execution of the ret/lret instruction. This patch fixes the above problem.

Signed-off-by: Prasanna S Panchamukhi <prasanna@xxxxxxxxxx>

---



---

 linux-2.6.12-rc1-prasanna/arch/i386/kernel/kprobes.c   |    7 +++++++
 linux-2.6.12-rc1-prasanna/arch/x86_64/kernel/kprobes.c |    7 +++++++
 2 files changed, 14 insertions(+)

diff -puN arch/i386/kernel/kprobes.c~kprobes-ret-address-fix arch/i386/kernel/kprobes.c
--- linux-2.6.12-rc1/arch/i386/kernel/kprobes.c~kprobes-ret-address-fix	2005-03-31 14:32:56.000000000 +0530
+++ linux-2.6.12-rc1-prasanna/arch/i386/kernel/kprobes.c	2005-03-31 14:37:24.000000000 +0530
@@ -218,6 +218,13 @@ static void resume_execution(struct kpro
 		*tos &= ~(TF_MASK | IF_MASK);
 		*tos |= kprobe_old_eflags;
 		break;
+	case 0xc3:		/* ret/lret */
+	case 0xcb:
+	case 0xc2:
+	case 0xca:
+		regs->eflags &= ~TF_MASK;
+		/* eip is already adjusted, no more changes required*/
+		return;
 	case 0xe8:		/* call relative - Fix return addr */
 		*tos = orig_eip + (*tos - copy_eip);
 		break;
diff -puN arch/x86_64/kernel/kprobes.c~kprobes-ret-address-fix arch/x86_64/kernel/kprobes.c
--- linux-2.6.12-rc1/arch/x86_64/kernel/kprobes.c~kprobes-ret-address-fix	2005-03-31 14:33:31.000000000 +0530
+++ linux-2.6.12-rc1-prasanna/arch/x86_64/kernel/kprobes.c	2005-03-31 14:37:08.000000000 +0530
@@ -231,6 +231,13 @@ static void resume_execution(struct kpro
 		*tos &= ~(TF_MASK | IF_MASK);
 		*tos |= kprobe_old_rflags;
 		break;
+	case 0xc3:		/* ret/lret */
+	case 0xcb:
+	case 0xc2:
+	case 0xca:
+		regs->eflags &= ~TF_MASK;
+		/* rip is already adjusted, no more changes required*/
+		return;
 	case 0xe8:		/* call relative - Fix return addr */
 		*tos = orig_rip + (*tos - copy_rip);
 		break;

_

Thanks
Prasanna
-- 

Prasanna S Panchamukhi
Linux Technology Center
India Software Labs, IBM Bangalore
Ph: 91-80-25044636
<prasanna@xxxxxxxxxx>
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