From: Dave Anderson <anderson@redhat.com>
Date: Wed, 23 Jan 2008 15:19:17 -0500
Subject: [misc] kprobes: fix reentrancy
Message-id: 4797A145.7020209@redhat.com
O-Subject: [RHEL5.2 PATCH 4/4] kprobes: BZ #232489: need kprobes improvement patches
Bugzilla: 232489

BZ #232489: need kprobes improvement patches
https://bugzilla.redhat.com/show_bug.cgi?id=232489
linux-2.6.git-cdc7dbdfe6edac177acb32e4ca56b525d0743fe7

Backport of this ia64-specific commit:

   commit cdc7dbdfe6edac177acb32e4ca56b525d0743fe7
   Author: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
   Date:   Fri May 11 09:38:40 2007 -0700

   [IA64] fix Kprobes reentrancy

   In case of reentrance i.e when a probe handler calls a functions which
   inturn has a probe, we save a previous kprobe information and just single
   step the reentrant probe without calling the actual probe handler.  During
   this reentracy period, if an interrupt occurs and if probe happens to
   trigger in the inturrupt path, then we were corrupting the previous kprobe(
   as we were overriding the previous kprobe info) info their by crashing the
   system.  This patch fixes this issues by having a an array of previous
   kprobe info struct(with the array size of 2).

   This similar technique is not needed on i386 and x86_64 because by default
   interrupts are turn off in the break/int3 exception handler.

   Signed-off-by: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
   Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
   Signed-off-by: Tony Luck <tony.luck@intel.com>

The testing of this piece on ia64 by Masami Hiramatsu (mhiramat@redhat.com)
showed that the upstream code was insufficient.  Masami developed a
bugfix patch and pushed it upstream on 1/17/08.  The new kprobes-ia64
maintainer has already reviewed it, but but it has not been merged
upstream yet.  That fix is appended below, which applies on top of
the currently upstream patch.

diff --git a/arch/ia64/kernel/kprobes.c b/arch/ia64/kernel/kprobes.c
index 570d938..e6b5e1e 100644
--- a/arch/ia64/kernel/kprobes.c
+++ b/arch/ia64/kernel/kprobes.c
@@ -303,14 +303,19 @@ static int __kprobes valid_kprobe_addr(int template, int slot,
 
 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 {
-	kcb->prev_kprobe.kp = kprobe_running();
-	kcb->prev_kprobe.status = kcb->kprobe_status;
+	unsigned int i;
+	i = atomic_add_return(1, &kcb->prev_kprobe_index);
+	kcb->prev_kprobe[i-1].kp = kprobe_running();
+	kcb->prev_kprobe[i-1].status = kcb->kprobe_status;
 }
 
 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 {
-	__get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
-	kcb->kprobe_status = kcb->prev_kprobe.status;
+	unsigned int i;
+	i = atomic_read(&kcb->prev_kprobe_index);
+	__get_cpu_var(current_kprobe) = kcb->prev_kprobe[i-1].kp;
+	kcb->kprobe_status = kcb->prev_kprobe[i-1].status;
+	atomic_sub(1, &kcb->prev_kprobe_index);
 }
 
 static void __kprobes set_current_kprobe(struct kprobe *p,
diff --git a/include/asm-ia64/kprobes.h b/include/asm-ia64/kprobes.h
index 8301061..f40eea1 100644
--- a/include/asm-ia64/kprobes.h
+++ b/include/asm-ia64/kprobes.h
@@ -71,13 +71,15 @@ struct prev_kprobe {
 
 #define	MAX_PARAM_RSE_SIZE	(0x60+0x60/0x3f)
 /* per-cpu kprobe control block */
+#define ARCH_PREV_KPROBE_SZ 2
 struct kprobe_ctlblk {
 	unsigned long kprobe_status;
 	struct pt_regs jprobe_saved_regs;
 	unsigned long jprobes_saved_stacked_regs[MAX_PARAM_RSE_SIZE];
 	unsigned long *bsp;
 	unsigned long cfm;
-	struct prev_kprobe prev_kprobe;
+	atomic_t prev_kprobe_index;
+	struct prev_kprobe prev_kprobe[ARCH_PREV_KPROBE_SZ];
 };
 
 #define JPROBE_ENTRY(pentry)	(kprobe_opcode_t *)pentry