kprobes: Allow kprobes coexist with livepatch

Allow kprobes which do not modify regs->ip, coexist with livepatch
by dropping FTRACE_OPS_FL_IPMODIFY from ftrace_ops.

User who wants to modify regs->ip (e.g. function fault injection)
must set a dummy post_handler to its kprobes when registering.
However, if such regs->ip modifying kprobes is set on a function,
that function can not be livepatched.

Link: http://lkml.kernel.org/r/156403587671.30117.5233558741694155985.stgit@devnote2

Acked-by: Joe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

1 files changed, 40 insertions, 16 deletions

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index d9770a5393c8..f57deec96ba1 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -962,8 +962,15 @@ static struct kprobe *alloc_aggr_kprobe(struct kprobe *p)
 #ifdef CONFIG_KPROBES_ON_FTRACE
 static struct ftrace_ops kprobe_ftrace_ops __read_mostly = {
         .func = kprobe_ftrace_handler,
+        .flags = FTRACE_OPS_FL_SAVE_REGS,
+};
+
+static struct ftrace_ops kprobe_ipmodify_ops __read_mostly = {
+        .func = kprobe_ftrace_handler,
         .flags = FTRACE_OPS_FL_SAVE_REGS | FTRACE_OPS_FL_IPMODIFY,
 };
+
+static int kprobe_ipmodify_enabled;
 static int kprobe_ftrace_enabled;
 
 /* Must ensure p->addr is really on ftrace */
@@ -976,58 +983,75 @@ static int prepare_kprobe(struct kprobe *p)
 }
 
 /* Caller must lock kprobe_mutex */
-static int arm_kprobe_ftrace(struct kprobe *p)
+static int __arm_kprobe_ftrace(struct kprobe *p, struct ftrace_ops *ops,
+                               int *cnt)
 {
         int ret = 0;
 
-        ret = ftrace_set_filter_ip(&kprobe_ftrace_ops,
-                                   (unsigned long)p->addr, 0, 0);
+        ret = ftrace_set_filter_ip(ops, (unsigned long)p->addr, 0, 0);
         if (ret) {
                 pr_debug("Failed to arm kprobe-ftrace at %pS (%d)\n",
                          p->addr, ret);
                 return ret;
         }
 
-        if (kprobe_ftrace_enabled == 0) {
-                ret = register_ftrace_function(&kprobe_ftrace_ops);
+        if (*cnt == 0) {
+                ret = register_ftrace_function(ops);
                 if (ret) {
                         pr_debug("Failed to init kprobe-ftrace (%d)\n", ret);
                         goto err_ftrace;
                 }
         }
 
-        kprobe_ftrace_enabled++;
+        (*cnt)++;
         return ret;
 
 err_ftrace:
         /*
-         * Note: Since kprobe_ftrace_ops has IPMODIFY set, and ftrace requires a
-         * non-empty filter_hash for IPMODIFY ops, we're safe from an accidental
-         * empty filter_hash which would undesirably trace all functions.
+         * At this point, sinec ops is not registered, we should be sefe from
+         * registering empty filter.
          */
-        ftrace_set_filter_ip(&kprobe_ftrace_ops, (unsigned long)p->addr, 1, 0);
+        ftrace_set_filter_ip(ops, (unsigned long)p->addr, 1, 0);
         return ret;
 }
 
+static int arm_kprobe_ftrace(struct kprobe *p)
+{
+        bool ipmodify = (p->post_handler != NULL);
+
+        return __arm_kprobe_ftrace(p,
+                ipmodify ? &kprobe_ipmodify_ops : &kprobe_ftrace_ops,
+                ipmodify ? &kprobe_ipmodify_enabled : &kprobe_ftrace_enabled);
+}
+
 /* Caller must lock kprobe_mutex */
-static int disarm_kprobe_ftrace(struct kprobe *p)
+static int __disarm_kprobe_ftrace(struct kprobe *p, struct ftrace_ops *ops,
+                                  int *cnt)
 {
         int ret = 0;
 
-        if (kprobe_ftrace_enabled == 1) {
-                ret = unregister_ftrace_function(&kprobe_ftrace_ops);
+        if (*cnt == 1) {
+                ret = unregister_ftrace_function(ops);
                 if (WARN(ret < 0, "Failed to unregister kprobe-ftrace (%d)\n", ret))
                         return ret;
         }
 
-        kprobe_ftrace_enabled--;
+        (*cnt)--;
 
-        ret = ftrace_set_filter_ip(&kprobe_ftrace_ops,
-                           (unsigned long)p->addr, 1, 0);
+        ret = ftrace_set_filter_ip(ops, (unsigned long)p->addr, 1, 0);
         WARN_ONCE(ret < 0, "Failed to disarm kprobe-ftrace at %pS (%d)\n",
                   p->addr, ret);
         return ret;
 }
+
+static int disarm_kprobe_ftrace(struct kprobe *p)
+{
+        bool ipmodify = (p->post_handler != NULL);
+
+        return __disarm_kprobe_ftrace(p,
+                ipmodify ? &kprobe_ipmodify_ops : &kprobe_ftrace_ops,
+                ipmodify ? &kprobe_ipmodify_enabled : &kprobe_ftrace_enabled);
+}
 #else   /* !CONFIG_KPROBES_ON_FTRACE */
 #define prepare_kprobe(p)       arch_prepare_kprobe(p)
 #define arm_kprobe_ftrace(p)    (-ENODEV)