[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>

5 files changed, 49 insertions, 0 deletions

diff --git a/arch/i386/kernel/kprobes.c b/arch/i386/kernel/kprobes.c
index 2f372dbd34fd..6483eeb1a4e8 100644
--- a/arch/i386/kernel/kprobes.c
+++ b/arch/i386/kernel/kprobes.c
@@ -188,6 +188,19 @@ static int __kprobes kprobe_handler(struct pt_regs *regs)
                         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 4de7f6759093..346fedf9ea47 100644
--- a/arch/ia64/kernel/kprobes.c
+++ b/arch/ia64/kernel/kprobes.c
@@ -638,6 +638,13 @@ static int __kprobes pre_kprobes_handler(struct die_args *args)
                         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 27b0c40601fb..cfab48566db1 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -179,6 +179,18 @@ static inline int kprobe_handler(struct pt_regs *regs)
                         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 ff5e9d5cad50..b9a9ce70e55c 100644
--- a/arch/sparc64/kernel/kprobes.c
+++ b/arch/sparc64/kernel/kprobes.c
@@ -135,6 +135,14 @@ static int __kprobes kprobe_handler(struct pt_regs *regs)
                         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 b7dc1f816d13..8b866a8572cf 100644
--- a/arch/x86_64/kernel/kprobes.c
+++ b/arch/x86_64/kernel/kprobes.c
@@ -334,6 +334,15 @@ int __kprobes kprobe_handler(struct pt_regs *regs)
                                 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;