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SubjectRe: [PATCH] ftrace: Fix use-after-free issue in ftrace_location()
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On 2024/4/10 23:28, Steven Rostedt wrote:
> On Mon, 1 Apr 2024 20:55:43 +0800
> Zheng Yejian <zhengyejian1@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 <zhengyejian1@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;
>> }
>>
>> /**
>


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