[PATCH v3 16/39] x86/ibt,ftrace: Search for __fentry__ location

Peter Zijlstra
2022-03-03T11:31:49Z

Have ftrace_location() search the symbol for the __fentry__ location
when it isn't at func+0 and use this for {,un}register_ftrace_direct().

This avoids a whole bunch of assumptions about __fentry__ being at
func+0.

Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
kernel/trace/ftrace.c | 34 +++++++++++++++++++++++++++++++---
1 file changed, 31 insertions(+), 3 deletions(-)

--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1578,7 +1578,25 @@ unsigned long ftrace_location_range(unsi
*/
unsigned long ftrace_location(unsigned long ip)
{
- return ftrace_location_range(ip, ip);
+ struct dyn_ftrace *rec;
+ unsigned long offset;
+ unsigned long size;
+
+ rec = lookup_rec(ip, ip);
+ if (!rec) {
+ if (!kallsyms_lookup_size_offset(ip, &size, &offset))
+ goto out;
+
+ /* map sym+0 to __fentry__ */
+ if (!offset)
+ rec = lookup_rec(ip, ip + size - 1);
+ }
+
+ if (rec)
+ return rec->ip;
+
+out:
+ return 0;
}

/**
@@ -4962,7 +4980,8 @@ ftrace_match_addr(struct ftrace_hash *ha
{
struct ftrace_func_entry *entry;

- if (!ftrace_location(ip))
+ ip = ftrace_location(ip);
+ if (!ip)
return -EINVAL;

if (remove) {
@@ -5110,11 +5129,16 @@ int register_ftrace_direct(unsigned long
struct ftrace_func_entry *entry;
struct ftrace_hash *free_hash = NULL;
struct dyn_ftrace *rec;
- int ret = -EBUSY;
+ int ret = -ENODEV;

mutex_lock(&direct_mutex);

+ ip = ftrace_location(ip);
+ if (!ip)
+ goto out_unlock;
+
/* See if there's a direct function at @ip already */
+ ret = -EBUSY;
if (ftrace_find_rec_direct(ip))
goto out_unlock;

@@ -5222,6 +5246,10 @@ int unregister_ftrace_direct(unsigned lo

mutex_lock(&direct_mutex);

+ ip = ftrace_location(ip);
+ if (!ip)
+ goto out_unlock;
+
entry = find_direct_entry(&ip, NULL);
if (!entry)
goto out_unlock;