ftrace: Fix possible use-after-free issue in ftrace_location()

KASAN reports a bug:

  BUG: KASAN: use-after-free in ftrace_location+0x90/0x120
  Read of size 8 at addr ffff888141d40010 by task insmod/424
  CPU: 8 PID: 424 Comm: insmod Tainted: G        W          6.9.0-rc2+
  [...]
  Call Trace:
   <TASK>
   dump_stack_lvl+0x68/0xa0
   print_report+0xcf/0x610
   kasan_report+0xb5/0xe0
   ftrace_location+0x90/0x120
   register_kprobe+0x14b/0xa40
   kprobe_init+0x2d/0xff0 [kprobe_example]
   do_one_initcall+0x8f/0x2d0
   do_init_module+0x13a/0x3c0
   load_module+0x3082/0x33d0
   init_module_from_file+0xd2/0x130
   __x64_sys_finit_module+0x306/0x440
   do_syscall_64+0x68/0x140
   entry_SYSCALL_64_after_hwframe+0x71/0x79

The root cause is that, in lookup_rec(), ftrace record of some address
is being searched in ftrace pages of some module, but those ftrace pages
at the same time is being freed in ftrace_release_mod() as the
corresponding module is being deleted:

           CPU1                       |      CPU2
  register_kprobes() {                | delete_module() {
    check_kprobe_address_safe() {     |
      arch_check_ftrace_location() {  |
        ftrace_location() {           |
          lookup_rec() // USE!        |   ftrace_release_mod() // Free!

To fix this issue:
  1. Hold rcu lock as accessing ftrace pages in ftrace_location_range();
  2. Use ftrace_location_range() instead of lookup_rec() in
     ftrace_location();
  3. Call synchronize_rcu() before freeing any ftrace pages both in
     ftrace_process_locs()/ftrace_release_mod()/ftrace_free_mem().

Link: https://lore.kernel.org/linux-trace-kernel/20240509192859.1273558-1-zhengyejian1@huawei.com
Cc: stable@vger.kernel.org
Cc: <mhiramat@kernel.org>
Cc: <mark.rutland@arm.com>
Cc: <mathieu.desnoyers@efficios.com>
Fixes: ae6aa16fdc16 ("kprobes: introduce ftrace based optimization")
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 5a01d72f66db534d9a632ee6ca1d8828c14896a9..2308c0a2fd29fe69a73900addf5d833a1c3bd9fc 100644 (file)
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1595,12 +1595,15 @@ static struct dyn_ftrace *lookup_rec(unsigned long start, unsigned long end)
 unsigned long ftrace_location_range(unsigned long start, unsigned long end)
 {
        struct dyn_ftrace *rec;
+       unsigned long ip = 0;
 
+       rcu_read_lock();
        rec = lookup_rec(start, end);
        if (rec)
-               return rec->ip;
+               ip = rec->ip;
+       rcu_read_unlock();
 
-       return 0;
+       return ip;
 }
 
 /**
@@ -1614,25 +1617,22 @@ unsigned long ftrace_location_range(unsigned long start, unsigned long end)
  */
 unsigned long ftrace_location(unsigned long ip)
 {
-       struct dyn_ftrace *rec;
+       unsigned long loc;
        unsigned long offset;
        unsigned long size;
 
-       rec = lookup_rec(ip, ip);
-       if (!rec) {
+       loc = ftrace_location_range(ip, ip);
+       if (!loc) {
                if (!kallsyms_lookup_size_offset(ip, &size, &offset))
                        goto out;
 
                /* map sym+0 to __fentry__ */
                if (!offset)
-                       rec = lookup_rec(ip, ip + size - 1);
+                       loc = ftrace_location_range(ip, ip + size - 1);
        }
 
-       if (rec)
-               return rec->ip;
-
 out:
-       return 0;
+       return loc;
 }
 
 /**
@@ -6591,6 +6591,8 @@ static int ftrace_process_locs(struct module *mod,
        /* We should have used all pages unless we skipped some */
        if (pg_unuse) {
                WARN_ON(!skipped);
+               /* Need to synchronize with ftrace_location_range() */
+               synchronize_rcu();
                ftrace_free_pages(pg_unuse);
        }
        return ret;
@@ -6804,6 +6806,9 @@ void ftrace_release_mod(struct module *mod)
  out_unlock:
        mutex_unlock(&ftrace_lock);
 
+       /* Need to synchronize with ftrace_location_range() */
+       if (tmp_page)
+               synchronize_rcu();
        for (pg = tmp_page; pg; pg = tmp_page) {
 
                /* Needs to be called outside of ftrace_lock */
@@ -7137,6 +7142,7 @@ void ftrace_free_mem(struct module *mod, void *start_ptr, void *end_ptr)
        unsigned long start = (unsigned long)(start_ptr);
        unsigned long end = (unsigned long)(end_ptr);
        struct ftrace_page **last_pg = &ftrace_pages_start;
+       struct ftrace_page *tmp_page = NULL;
        struct ftrace_page *pg;
        struct dyn_ftrace *rec;
        struct dyn_ftrace key;
@@ -7178,12 +7184,8 @@ void ftrace_free_mem(struct module *mod, void *start_ptr, void *end_ptr)
                ftrace_update_tot_cnt--;
                if (!pg->index) {
                        *last_pg = pg->next;
-                       if (pg->records) {
-                               free_pages((unsigned long)pg->records, pg->order);
-                               ftrace_number_of_pages -= 1 << pg->order;
-                       }
-                       ftrace_number_of_groups--;
-                       kfree(pg);
+                       pg->next = tmp_page;
+                       tmp_page = pg;
                        pg = container_of(last_pg, struct ftrace_page, next);
                        if (!(*last_pg))
                                ftrace_pages = pg;
@@ -7200,6 +7202,11 @@ void ftrace_free_mem(struct module *mod, void *start_ptr, void *end_ptr)
                clear_func_from_hashes(func);
                kfree(func);
        }
+       /* Need to synchronize with ftrace_location_range() */
+       if (tmp_page) {
+               synchronize_rcu();
+               ftrace_free_pages(tmp_page);
+       }
 }
 
 void __init ftrace_free_init_mem(void)