From: Masami Hiramatsu <mhiramat@redhat.com>
Date: Wed, 22 Apr 2009 09:32:26 -0400
Subject: [x86] prevent boosting kprobes on exception address
Message-id: 49EF1C6A.7010405@redhat.com
O-Subject: [RHEL 5.4 PATCH] BZ493088 kprobes: x86-64/i386: Prevent boosting kprobes on exception address
Bugzilla: 493088
RH-Acked-by: Dave Anderson <anderson@redhat.com>
RH-Acked-by: Prarit Bhargava <prarit@redhat.com>

Bugzilla:
https://bugzilla.redhat.com/show_bug.cgi?id=493088

Description:
Prevent boosting kprobes on exception address.

Don't boost at the addresses which are listed on exception tables,
because major page fault can occur on those addresses.  In that case,
kprobes can not ensure that when instruction buffer can be freed since
some processes will sleep on the buffer.

kprobes-ia64 already has same check.

Upstream status:
This fix has been in upstream.
commit 30390880debce4a68fd23e87a787f27609e4bf4a

Brew:
Built on all platforms.
https://brewweb.devel.redhat.com//taskinfo?taskID=1768152

Test status:
I checked that kprobes put on the address in ex_table were not boosted
with this patch, on both of x86_64 and i686.

diff --git a/arch/i386/kernel/kprobes.c b/arch/i386/kernel/kprobes.c
index fbcad23..149e8b9 100644
--- a/arch/i386/kernel/kprobes.c
+++ b/arch/i386/kernel/kprobes.c
@@ -31,6 +31,7 @@
 #include <linux/kprobes.h>
 #include <linux/ptrace.h>
 #include <linux/preempt.h>
+#include <linux/module.h>
 #include <asm/cacheflush.h>
 #include <asm/kdebug.h>
 #include <asm/desc.h>
@@ -100,6 +101,10 @@ static __always_inline int can_boost(kprobe_opcode_t *opcodes)
 #undef W
 	kprobe_opcode_t opcode;
 	kprobe_opcode_t *orig_opcodes = opcodes;
+
+	if (search_exception_tables(opcodes))
+		return 0;	/* Page fault may occur on this address. */
+
 retry:
 	if (opcodes - orig_opcodes > MAX_INSN_SIZE - 1)
 		return 0;
diff --git a/arch/x86_64/kernel/kprobes.c b/arch/x86_64/kernel/kprobes.c
index 8a5b93f..005a0de 100644
--- a/arch/x86_64/kernel/kprobes.c
+++ b/arch/x86_64/kernel/kprobes.c
@@ -129,6 +129,9 @@ static __always_inline int can_boost(kprobe_opcode_t *opcodes)
 	kprobe_opcode_t opcode;
 	kprobe_opcode_t *orig_opcodes = opcodes;
 
+	if (search_exception_tables(opcodes))
+		return 0;	/* Page fault may occur on this address. */
+
 retry:
 	if (opcodes - orig_opcodes > __MAX_INSN_SIZE - 1)
 		return 0;