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authorMasami Hiramatsu <mhiramat@kernel.org>2019-02-24 01:49:52 +0900
committerIngo Molnar <mingo@kernel.org>2019-04-19 14:26:05 +0200
commit3ff9c075cc767b3060bdac12da72fc94dd7da1b8 (patch)
tree68514aa6c9c1556f490fc7e729562f2b18a593f1
parent3fe3331bb285700ab2253dbb07f8e478fcea2f1b (diff)
downloadlwn-3ff9c075cc767b3060bdac12da72fc94dd7da1b8.tar.gz
lwn-3ff9c075cc767b3060bdac12da72fc94dd7da1b8.zip
x86/kprobes: Verify stack frame on kretprobe
Verify the stack frame pointer on kretprobe trampoline handler, If the stack frame pointer does not match, it skips the wrong entry and tries to find correct one. This can happen if user puts the kretprobe on the function which can be used in the path of ftrace user-function call. Such functions should not be probed, so this adds a warning message that reports which function should be blacklisted. Tested-by: Andrea Righi <righi.andrea@gmail.com> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org> Acked-by: Steven Rostedt <rostedt@goodmis.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/155094059185.6137.15527904013362842072.stgit@devbox Signed-off-by: Ingo Molnar <mingo@kernel.org>
-rw-r--r--arch/x86/kernel/kprobes/core.c26
-rw-r--r--include/linux/kprobes.h1
2 files changed, 27 insertions, 0 deletions
diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index a034cb808e7e..18fbe9be2d68 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -569,6 +569,7 @@ void arch_prepare_kretprobe(struct kretprobe_instance *ri, struct pt_regs *regs)
unsigned long *sara = stack_addr(regs);
ri->ret_addr = (kprobe_opcode_t *) *sara;
+ ri->fp = sara;
/* Replace the return addr with trampoline addr */
*sara = (unsigned long) &kretprobe_trampoline;
@@ -759,15 +760,21 @@ static __used void *trampoline_handler(struct pt_regs *regs)
unsigned long flags, orig_ret_address = 0;
unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;
kprobe_opcode_t *correct_ret_addr = NULL;
+ void *frame_pointer;
+ bool skipped = false;
INIT_HLIST_HEAD(&empty_rp);
kretprobe_hash_lock(current, &head, &flags);
/* fixup registers */
#ifdef CONFIG_X86_64
regs->cs = __KERNEL_CS;
+ /* On x86-64, we use pt_regs->sp for return address holder. */
+ frame_pointer = &regs->sp;
#else
regs->cs = __KERNEL_CS | get_kernel_rpl();
regs->gs = 0;
+ /* On x86-32, we use pt_regs->flags for return address holder. */
+ frame_pointer = &regs->flags;
#endif
regs->ip = trampoline_address;
regs->orig_ax = ~0UL;
@@ -789,8 +796,25 @@ static __used void *trampoline_handler(struct pt_regs *regs)
if (ri->task != current)
/* another task is sharing our hash bucket */
continue;
+ /*
+ * Return probes must be pushed on this hash list correct
+ * order (same as return order) so that it can be poped
+ * correctly. However, if we find it is pushed it incorrect
+ * order, this means we find a function which should not be
+ * probed, because the wrong order entry is pushed on the
+ * path of processing other kretprobe itself.
+ */
+ if (ri->fp != frame_pointer) {
+ if (!skipped)
+ pr_warn("kretprobe is stacked incorrectly. Trying to fixup.\n");
+ skipped = true;
+ continue;
+ }
orig_ret_address = (unsigned long)ri->ret_addr;
+ if (skipped)
+ pr_warn("%ps must be blacklisted because of incorrect kretprobe order\n",
+ ri->rp->kp.addr);
if (orig_ret_address != trampoline_address)
/*
@@ -808,6 +832,8 @@ static __used void *trampoline_handler(struct pt_regs *regs)
if (ri->task != current)
/* another task is sharing our hash bucket */
continue;
+ if (ri->fp != frame_pointer)
+ continue;
orig_ret_address = (unsigned long)ri->ret_addr;
if (ri->rp && ri->rp->handler) {
diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index 201f0f2683f2..9a897256e481 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -173,6 +173,7 @@ struct kretprobe_instance {
struct kretprobe *rp;
kprobe_opcode_t *ret_addr;
struct task_struct *task;
+ void *fp;
char data[0];
};