[PATCH 6/7] kprobes/ftrace: Use ftrace_location() when [dis]arming probes

[Naveen N. Rao]

Ftrace location could include more than a single instruction in case of
some architectures (powerpc64, for now). In this case, kprobe is
permitted on any of those instructions, and uses ftrace infrastructure
for functioning.

However, [dis]arm_kprobe_ftrace() uses the kprobe address when setting
up ftrace filter IP. This won't work if the address points to any
instruction apart from the one that has a branch to _mcount(). To
resolve this, have [dis]arm_kprobe_ftrace() use ftrace_function() to
identify the filter IP.

Signed-off-by: Naveen N. Rao <naveen.n....@linux.vnet.ibm.com>
---
 kernel/kprobes.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 445337c107e0..282ee704e2d8 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -978,10 +978,10 @@ static int prepare_kprobe(struct kprobe *p)
 /* Caller must lock kprobe_mutex */
 static int arm_kprobe_ftrace(struct kprobe *p)
 {
+       unsigned long ftrace_ip = ftrace_location((unsigned long)p->addr);
        int ret = 0;
 
-       ret = ftrace_set_filter_ip(&kprobe_ftrace_ops,
-                                  (unsigned long)p->addr, 0, 0);
+       ret = ftrace_set_filter_ip(&kprobe_ftrace_ops, ftrace_ip, 0, 0);
        if (ret) {
                pr_debug("Failed to arm kprobe-ftrace at %pS (%d)\n",
                         p->addr, ret);
@@ -1005,13 +1005,14 @@ static int arm_kprobe_ftrace(struct kprobe *p)
         * non-empty filter_hash for IPMODIFY ops, we're safe from an accidental
         * empty filter_hash which would undesirably trace all functions.
         */
-       ftrace_set_filter_ip(&kprobe_ftrace_ops, (unsigned long)p->addr, 1, 0);
+       ftrace_set_filter_ip(&kprobe_ftrace_ops, ftrace_ip, 1, 0);
        return ret;
 }
 
 /* Caller must lock kprobe_mutex */
 static int disarm_kprobe_ftrace(struct kprobe *p)
 {
+       unsigned long ftrace_ip = ftrace_location((unsigned long)p->addr);
        int ret = 0;
 
        if (kprobe_ftrace_enabled == 1) {
@@ -1022,8 +1023,7 @@ static int disarm_kprobe_ftrace(struct kprobe *p)
 
        kprobe_ftrace_enabled--;
 
-       ret = ftrace_set_filter_ip(&kprobe_ftrace_ops,
-                          (unsigned long)p->addr, 1, 0);
+       ret = ftrace_set_filter_ip(&kprobe_ftrace_ops, ftrace_ip, 1, 0);
        WARN_ONCE(ret < 0, "Failed to disarm kprobe-ftrace at %pS (%d)\n",
                  p->addr, ret);
        return ret;
-- 
2.22.0