[PATCH] kprobes: fix race in recovery of reentrant probe
There is a window where a probe gets removed right after the probe is hit
on some different cpu. In this case probe handlers can't find a matching
probe instance related to break address. In this case we need to read the
original instruction at break address to see if that is not a break/int3
instruction and recover safely.
Previous code had a bug where we were not checking for the above race in
case of reentrant probes and the below patch fixes this race.
Tested on IA64, Powerpc, x86_64.
Signed-off-by: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/arch/i386/kernel/kprobes.c b/arch/i386/kernel/kprobes.c
index 2f372db..6483eeb 100644
--- a/arch/i386/kernel/kprobes.c
+++ b/arch/i386/kernel/kprobes.c
@@ -188,6 +188,19 @@
kcb->kprobe_status = KPROBE_REENTER;
return 1;
} else {
+ if (regs->eflags & VM_MASK) {
+ /* We are in virtual-8086 mode. Return 0 */
+ goto no_kprobe;
+ }
+ if (*addr != BREAKPOINT_INSTRUCTION) {
+ /* The breakpoint instruction was removed by
+ * another cpu right after we hit, no further
+ * handling of this interrupt is appropriate
+ */
+ regs->eip -= sizeof(kprobe_opcode_t);
+ ret = 1;
+ goto no_kprobe;
+ }
p = __get_cpu_var(current_kprobe);
if (p->break_handler && p->break_handler(p, regs)) {
goto ss_probe;
diff --git a/arch/ia64/kernel/kprobes.c b/arch/ia64/kernel/kprobes.c
index 4de7f67..346fedf 100644
--- a/arch/ia64/kernel/kprobes.c
+++ b/arch/ia64/kernel/kprobes.c
@@ -638,6 +638,13 @@
if (p->break_handler && p->break_handler(p, regs)) {
goto ss_probe;
}
+ } else if (!is_ia64_break_inst(regs)) {
+ /* The breakpoint instruction was removed by
+ * another cpu right after we hit, no further
+ * handling of this interrupt is appropriate
+ */
+ ret = 1;
+ goto no_kprobe;
} else {
/* Not our break */
goto no_kprobe;
diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index 27b0c40..cfab485 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -179,6 +179,18 @@
kcb->kprobe_status = KPROBE_REENTER;
return 1;
} else {
+ if (*addr != BREAKPOINT_INSTRUCTION) {
+ /* If trap variant, then it belongs not to us */
+ kprobe_opcode_t cur_insn = *addr;
+ if (is_trap(cur_insn))
+ goto no_kprobe;
+ /* The breakpoint instruction was removed by
+ * another cpu right after we hit, no further
+ * handling of this interrupt is appropriate
+ */
+ ret = 1;
+ goto no_kprobe;
+ }
p = __get_cpu_var(current_kprobe);
if (p->break_handler && p->break_handler(p, regs)) {
goto ss_probe;
diff --git a/arch/sparc64/kernel/kprobes.c b/arch/sparc64/kernel/kprobes.c
index ff5e9d5..b9a9ce7 100644
--- a/arch/sparc64/kernel/kprobes.c
+++ b/arch/sparc64/kernel/kprobes.c
@@ -135,6 +135,14 @@
prepare_singlestep(p, regs, kcb);
return 1;
} else {
+ if (*(u32 *)addr != BREAKPOINT_INSTRUCTION) {
+ /* The breakpoint instruction was removed by
+ * another cpu right after we hit, no further
+ * handling of this interrupt is appropriate
+ */
+ ret = 1;
+ goto no_kprobe;
+ }
p = __get_cpu_var(current_kprobe);
if (p->break_handler && p->break_handler(p, regs))
goto ss_probe;
diff --git a/arch/x86_64/kernel/kprobes.c b/arch/x86_64/kernel/kprobes.c
index b7dc1f8..8b866a8 100644
--- a/arch/x86_64/kernel/kprobes.c
+++ b/arch/x86_64/kernel/kprobes.c
@@ -334,6 +334,15 @@
return 1;
}
} else {
+ if (*addr != BREAKPOINT_INSTRUCTION) {
+ /* The breakpoint instruction was removed by
+ * another cpu right after we hit, no further
+ * handling of this interrupt is appropriate
+ */
+ regs->rip = (unsigned long)addr;
+ ret = 1;
+ goto no_kprobe;
+ }
p = __get_cpu_var(current_kprobe);
if (p->break_handler && p->break_handler(p, regs)) {
goto ss_probe;