Re: [PATCH] Kprobes: Print details of kretprobe on assertion failure

[Ananth N Mavinakayanahalli]

On Mon, Apr 02, 2007 at 02:17:32PM -0700, Andrew Morton wrote:
> On Mon, 2 Apr 2007 14:56:36 +0530
> Ananth N Mavinakayanahalli <ananth@xxxxxxxxxx> wrote:
> 
> > From: Ananth N Mavinakayanahalli <ananth@xxxxxxxxxx>
> > 
> > In certain cases like when the real return address can't be found or
> > when the number of tracked calls to a kretprobed function is less than
> > the number of returns, we may not be able to find the correct return
> > address after processing a kretprobe. Currently we just do a BUG_ON, but
> > no information is provided about the actual failing kretprobe.
> > 
> > Print out details of the kretprobe before calling BUG().
> > 
> > Signed-off-by: Ananth N Mavinakayanahalli <ananth@xxxxxxxxxx>
> > 
> > ---
> >  arch/i386/kernel/kprobes.c    |    6 +++++-
> >  arch/ia64/kernel/kprobes.c    |    7 ++++++-
> >  arch/powerpc/kernel/kprobes.c |    7 ++++++-
> >  arch/x86_64/kernel/kprobes.c  |    7 ++++++-
> >  4 files changed, 23 insertions(+), 4 deletions(-)
> > 
> > Index: linux-2.6.21-rc5/arch/i386/kernel/kprobes.c
> > ===================================================================
> > --- linux-2.6.21-rc5.orig/arch/i386/kernel/kprobes.c
> > +++ linux-2.6.21-rc5/arch/i386/kernel/kprobes.c
> > @@ -440,7 +440,11 @@ fastcall void *__kprobes trampoline_hand
> >  			break;
> >  	}
> >  
> > -	BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
> > +	if (!orig_ret_address || (orig_ret_address == trampoline_address)) {
> > +		printk("kretprobe BUG!: Processing kretprobe %p @ %p\n",
> > +				ri->rp, ri->rp->kp.addr);
> > +		BUG();
> > +	}
> >  
> >  	spin_unlock_irqrestore(&kretprobe_lock, flags);
> >  
> > Index: linux-2.6.21-rc5/arch/ia64/kernel/kprobes.c
> > ===================================================================
> > --- linux-2.6.21-rc5.orig/arch/ia64/kernel/kprobes.c
> > +++ linux-2.6.21-rc5/arch/ia64/kernel/kprobes.c
> > @@ -444,7 +444,12 @@ int __kprobes trampoline_probe_handler(s
> >  			break;
> >  	}
> >  
> > -	BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
> > +	if (!orig_ret_address || (orig_ret_address == trampoline_address)) {
> > +		printk("kretprobe BUG!: Processing kretprobe %p @ %p\n",
> > +				ri->rp, ri->rp->kp.addr);
> > +		BUG();
> > +	}
> > +
> >  	regs->cr_iip = orig_ret_address;
> >  
> >  	reset_current_kprobe();
> > Index: linux-2.6.21-rc5/arch/powerpc/kernel/kprobes.c
> > ===================================================================
> > --- linux-2.6.21-rc5.orig/arch/powerpc/kernel/kprobes.c
> > +++ linux-2.6.21-rc5/arch/powerpc/kernel/kprobes.c
> > @@ -293,7 +293,12 @@ int __kprobes trampoline_probe_handler(s
> >  			break;
> >  	}
> >  
> > -	BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
> > +	if (!orig_ret_address || (orig_ret_address == trampoline_address)) {
> > +		printk("kretprobe BUG!: Processing kretprobe %p @ %p\n",
> > +				ri->rp, ri->rp->kp.addr);
> > +		BUG();
> > +	}
> > +
> >  	regs->nip = orig_ret_address;
> >  
> >  	reset_current_kprobe();
> > Index: linux-2.6.21-rc5/arch/x86_64/kernel/kprobes.c
> > ===================================================================
> > --- linux-2.6.21-rc5.orig/arch/x86_64/kernel/kprobes.c
> > +++ linux-2.6.21-rc5/arch/x86_64/kernel/kprobes.c
> > @@ -438,7 +438,12 @@ int __kprobes trampoline_probe_handler(s
> >  			break;
> >  	}
> >  
> > -	BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
> > +	if (!orig_ret_address || (orig_ret_address == trampoline_address)) {
> > +		printk("kretprobe BUG!: Processing kretprobe %p @ %p\n",
> > +				ri->rp, ri->rp->kp.addr);
> > +		BUG();
> > +	}
> > +
> >  	regs->rip = orig_ret_address;
> >  
> 
> A lot of copying-and-pasting there.  Would it be better if this assertion
> was performed in a library function in kernel/kprobes.c?

Indeed. Here is the updated patch...

From: Ananth N Mavinakayanahalli <ananth@xxxxxxxxxx>

In certain cases like when the real return address can't be found or
when the number of tracked calls to a kretprobed function is less than
the number of returns, we may not be able to find the correct return
address after processing a kretprobe. Currently we just do a BUG_ON, but
no information is provided about the actual failing kretprobe.

Print out details of the kretprobe before calling BUG().

Signed-off-by: Ananth N Mavinakayanahalli <ananth@xxxxxxxxxx>

---
 arch/i386/kernel/kprobes.c    |    3 +--
 arch/ia64/kernel/kprobes.c    |    3 ++-
 arch/powerpc/kernel/kprobes.c |    2 +-
 arch/x86_64/kernel/kprobes.c  |    2 +-
 include/linux/kprobes.h       |   10 ++++++++++
 5 files changed, 15 insertions(+), 5 deletions(-)

Index: linux-2.6.21-rc5/arch/i386/kernel/kprobes.c
===================================================================
--- linux-2.6.21-rc5.orig/arch/i386/kernel/kprobes.c
+++ linux-2.6.21-rc5/arch/i386/kernel/kprobes.c
@@ -440,8 +440,7 @@ fastcall void *__kprobes trampoline_hand
 			break;
 	}
 
-	BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
-
+	kretprobe_assert(ri, orig_ret_address, trampoline_address);
 	spin_unlock_irqrestore(&kretprobe_lock, flags);
 
 	hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
Index: linux-2.6.21-rc5/arch/ia64/kernel/kprobes.c
===================================================================
--- linux-2.6.21-rc5.orig/arch/ia64/kernel/kprobes.c
+++ linux-2.6.21-rc5/arch/ia64/kernel/kprobes.c
@@ -444,7 +444,8 @@ int __kprobes trampoline_probe_handler(s
 			break;
 	}
 
-	BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
+	kretprobe_assert(ri, orig_ret_address, trampoline_address);
+
 	regs->cr_iip = orig_ret_address;
 
 	reset_current_kprobe();
Index: linux-2.6.21-rc5/arch/powerpc/kernel/kprobes.c
===================================================================
--- linux-2.6.21-rc5.orig/arch/powerpc/kernel/kprobes.c
+++ linux-2.6.21-rc5/arch/powerpc/kernel/kprobes.c
@@ -293,7 +293,7 @@ int __kprobes trampoline_probe_handler(s
 			break;
 	}
 
-	BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
+	kretprobe_assert(ri, orig_ret_address, trampoline_address);
 	regs->nip = orig_ret_address;
 
 	reset_current_kprobe();
Index: linux-2.6.21-rc5/arch/x86_64/kernel/kprobes.c
===================================================================
--- linux-2.6.21-rc5.orig/arch/x86_64/kernel/kprobes.c
+++ linux-2.6.21-rc5/arch/x86_64/kernel/kprobes.c
@@ -438,7 +438,7 @@ int __kprobes trampoline_probe_handler(s
 			break;
 	}
 
-	BUG_ON(!orig_ret_address || (orig_ret_address == trampoline_address));
+	kretprobe_assert(ri, orig_ret_address, trampoline_address);
 	regs->rip = orig_ret_address;
 
 	reset_current_kprobe();
Index: linux-2.6.21-rc5/include/linux/kprobes.h
===================================================================
--- linux-2.6.21-rc5.orig/include/linux/kprobes.h
+++ linux-2.6.21-rc5/include/linux/kprobes.h
@@ -158,6 +158,16 @@ struct kretprobe_instance {
 	struct task_struct *task;
 };
 
+static inline void kretprobe_assert(struct kretprobe_instance *ri,
+	unsigned long orig_ret_address, unsigned long trampoline_address)
+{
+	if (!orig_ret_address || (orig_ret_address == trampoline_address)) {
+		printk("kretprobe BUG!: Processing kretprobe %p @ %p\n",
+				ri->rp, ri->rp->kp.addr);
+		BUG();
+	}
+}
+
 extern spinlock_t kretprobe_lock;
 extern struct mutex kprobe_mutex;
 extern int arch_prepare_kprobe(struct kprobe *p);
-
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