On Thu, May 12, 2022 at 3:08 PM Song Liu song@kernel.org wrote:

We see the following GPF when register_ftrace_direct fails:

[ ] general protection fault, probably for non-canonical address \ 0x200000000000010: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC PTI [...] [ ] RIP: 0010:ftrace_find_rec_direct+0x53/0x70 [ ] Code: 48 c1 e0 03 48 03 42 08 48 8b 10 31 c0 48 85 d2 74 [...] [ ] RSP: 0018:ffffc9000138bc10 EFLAGS: 00010206 [ ] RAX: 0000000000000000 RBX: ffffffff813e0df0 RCX: 000000000000003b [ ] RDX: 0200000000000000 RSI: 000000000000000c RDI: ffffffff813e0df0 [ ] RBP: ffffffffa00a3000 R08: ffffffff81180ce0 R09: 0000000000000001 [ ] R10: ffffc9000138bc18 R11: 0000000000000001 R12: ffffffff813e0df0 [ ] R13: ffffffff813e0df0 R14: ffff888171b56400 R15: 0000000000000000 [ ] FS: 00007fa9420c7780(0000) GS:ffff888ff6a00000(0000) knlGS:000000000 [ ] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ ] CR2: 000000000770d000 CR3: 0000000107d50003 CR4: 0000000000370ee0 [ ] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ ] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ ] Call Trace: [ ] <TASK> [ ] register_ftrace_direct+0x54/0x290 [ ] ? render_sigset_t+0xa0/0xa0 [ ] bpf_trampoline_update+0x3f5/0x4a0 [ ] ? 0xffffffffa00a3000 [ ] bpf_trampoline_link_prog+0xa9/0x140 [ ] bpf_tracing_prog_attach+0x1dc/0x450 [ ] bpf_raw_tracepoint_open+0x9a/0x1e0 [ ] ? find_held_lock+0x2d/0x90 [ ] ? lock_release+0x150/0x430 [ ] __sys_bpf+0xbd6/0x2700 [ ] ? lock_is_held_type+0xd8/0x130 [ ] __x64_sys_bpf+0x1c/0x20 [ ] do_syscall_64+0x3a/0x80 [ ] entry_SYSCALL_64_after_hwframe+0x44/0xae [ ] RIP: 0033:0x7fa9421defa9 [ ] Code: 00 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 9 f8 [...] [ ] RSP: 002b:00007ffed743bd78 EFLAGS: 00000246 ORIG_RAX: 0000000000000141 [ ] RAX: ffffffffffffffda RBX: 00000000069d2480 RCX: 00007fa9421defa9 [ ] RDX: 0000000000000078 RSI: 00007ffed743bd80 RDI: 0000000000000011 [ ] RBP: 00007ffed743be00 R08: 0000000000bb7270 R09: 0000000000000000 [ ] R10: 00000000069da210 R11: 0000000000000246 R12: 0000000000000001 [ ] R13: 00007ffed743c4b0 R14: 00000000069d2480 R15: 0000000000000001 [ ] </TASK> [ ] Modules linked in: klp_vm(OK) [ ] ---[ end trace 0000000000000000 ]---

One way to trigger this is:

1. load a livepatch that patches kernel function xxx;
2. run bpftrace -e 'kfunc:xxx {}', this will fail (expected for now);
3. repeat #2 => gpf.

This is because the entry is added to direct_functions, but not removed. Fix this by remove the entry from direct_functions when register_ftrace_direct fails.

Also remove the last trailing space from ftrace.c, so we don't have to worry about it anymore.

Cc: stable@vger.kernel.org Fixes: 763e34e74bb7 ("ftrace: Add register_ftrace_direct()") Signed-off-by: Song Liu song@kernel.org

Hi Steven,

Could you please share your thoughts on this fix?

Thanks, Song

---

kernel/trace/ftrace.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 4f1d2f5e7263..375293c5f3e9 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -4465,7 +4465,7 @@ int ftrace_func_mapper_add_ip(struct ftrace_func_mapper *mapper,

• @ip: The instruction pointer address to remove the data from
• Returns the data if it is found, otherwise NULL.

• • Note, if the data pointer is used as the data itself, (see

• • Note, if the data pointer is used as the data itself, (see
  • ftrace_func_mapper_find_ip(), then the return value may be meaningless,
  • if the data pointer was set to zero.
  */

@@ -5200,8 +5200,10 @@ int register_ftrace_direct(unsigned long ip, unsigned long addr)

    if (!ret && !(direct_ops.flags & FTRACE_OPS_FL_ENABLED)) {
            ret = register_ftrace_function(&direct_ops);

•           if (ret)
  

•           if (ret) {
                    ftrace_set_filter_ip(&direct_ops, ip, 1, 0);
  

•                   remove_hash_entry(direct_functions, entry);
  

•           }
    }
  
    if (ret) {
  

-- 2.30.2

On Thu, 12 May 2022 15:08:08 -0700 Song Liu song@kernel.org wrote:

--- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -4465,7 +4465,7 @@ int ftrace_func_mapper_add_ip(struct ftrace_func_mapper *mapper,

• @ip: The instruction pointer address to remove the data from
• Returns the data if it is found, otherwise NULL.

• • Note, if the data pointer is used as the data itself, (see

• • Note, if the data pointer is used as the data itself, (see
  • ftrace_func_mapper_find_ip(), then the return value may be meaningless,
  • if the data pointer was set to zero.
  */

@@ -5200,8 +5200,10 @@ int register_ftrace_direct(unsigned long ip, unsigned long addr) if (!ret && !(direct_ops.flags & FTRACE_OPS_FL_ENABLED)) { ret = register_ftrace_function(&direct_ops);

• if (ret)
  

• if (ret) {
  ftrace_set_filter_ip(&direct_ops, ip, 1, 0);
  

• 	remove_hash_entry(direct_functions, entry);
  

• }
  

  }

if (ret) {

Perhaps something like this is more robust?

-- Steve

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 4f1d2f5e7263..cd38ad490174 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -5195,8 +5195,6 @@ int register_ftrace_direct(unsigned long ip, unsigned long addr) goto out_unlock;

ret = ftrace_set_filter_ip(&direct_ops, ip, 0, 0); - if (ret) - remove_hash_entry(direct_functions, entry);

if (!ret && !(direct_ops.flags & FTRACE_OPS_FL_ENABLED)) { ret = register_ftrace_function(&direct_ops); @@ -5205,6 +5203,7 @@ int register_ftrace_direct(unsigned long ip, unsigned long addr) }

if (ret) { + remove_hash_entry(direct_functions, entry); kfree(entry); if (!direct->count) { list_del_rcu(&direct->next);