On 2024/4/10 23:28, Steven Rostedt wrote:
On Mon, 1 Apr 2024 20:55:43 +0800
Zheng Yejian <zhengyeji...@huawei.com> wrote:
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+ #213
[...]
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 when lookup_rec() is lookuping ftrace record of
an address in some module, and at the same time in ftrace_release_mod(),
the memory that saving ftrace records has been freed as that module is
being deleted.
register_kprobes() {
check_kprobe_address_safe() {
arch_check_ftrace_location() {
ftrace_location() {
lookup_rec() // access memory that has been freed by
// ftrace_release_mod() !!!
It seems that the ftrace_lock is required when lookuping records in
ftrace_location(), so is ftrace_location_range().
Fixes: ae6aa16fdc16 ("kprobes: introduce ftrace based optimization")
Signed-off-by: Zheng Yejian <zhengyeji...@huawei.com>
---
kernel/trace/ftrace.c | 28 ++++++++++++++++++----------
1 file changed, 18 insertions(+), 10 deletions(-)
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index da1710499698..838d175709c1 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1581,7 +1581,7 @@ static struct dyn_ftrace *lookup_rec(unsigned long start,
unsigned long end)
}
/**
- * ftrace_location_range - return the first address of a traced location
+ * ftrace_location_range_locked - return the first address of a traced location
* if it touches the given ip range
* @start: start of range to search.
* @end: end of range to search (inclusive). @end points to the last byte
@@ -1592,7 +1592,7 @@ static struct dyn_ftrace *lookup_rec(unsigned long start,
unsigned long end)
* that is either a NOP or call to the function tracer. It checks the ftrace
* internal tables to determine if the address belongs or not.
*/
-unsigned long ftrace_location_range(unsigned long start, unsigned long end)
+static unsigned long ftrace_location_range_locked(unsigned long start,
unsigned long end)
{
struct dyn_ftrace *rec;
@@ -1603,6 +1603,17 @@ unsigned long ftrace_location_range(unsigned long start, unsigned long end)
return 0;
}
+unsigned long ftrace_location_range(unsigned long start, unsigned long end)
+{
+ unsigned long loc;
+
+ mutex_lock(&ftrace_lock);
+ loc = ftrace_location_range_locked(start, end);
+ mutex_unlock(&ftrace_lock);
I'm not so sure we can take a mutex in all places that call this function.
What about using RCU?
rcu_read_lock();
loc = ftrace_location_range_rcu(start, end);
rcu_read_unlock();
Then in ftrace_release_mod() we can have:
out_unlock:
mutex_unlock();
/* Need to synchronize with ftrace_location() */
if (tmp_pages)
synchronize_rcu();
-- Steve
Yes, it is better to use RCU, I'll do it in v2.
--
Thanks
Zheng Yejian
+
+ return loc;
+}
+
/**
* ftrace_location - return the ftrace location
* @ip: the instruction pointer to check
@@ -1614,25 +1625,22 @@ 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;
}
/**
