On Fri, 28 Aug 2020 13:11:15 +0000
"Eddy_Wu@xxxxxxxxxxxxxx" <Eddy_Wu@xxxxxxxxxxxxxx> wrote:
> > -----Original Message-----
> > From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Sent: Friday, August 28, 2020 12:13 AM
> > To: linux-kernel@xxxxxxxxxxxxxxx; mhiramat@xxxxxxxxxx
> > Cc: Eddy Wu (RD-TW) <Eddy_Wu@xxxxxxxxxxxxxx>; x86@xxxxxxxxxx; davem@xxxxxxxxxxxxx; rostedt@xxxxxxxxxxx;
> > naveen.n.rao@xxxxxxxxxxxxx; anil.s.keshavamurthy@xxxxxxxxx; linux-arch@xxxxxxxxxxxxxxx; cameron@xxxxxxxxxxxxxx;
> > oleg@xxxxxxxxxx; will@xxxxxxxxxx; paulmck@xxxxxxxxxx; peterz@xxxxxxxxxxxxx
> > Subject: [RFC][PATCH 3/7] kprobes: Remove kretprobe hash
> >
> > @@ -1935,71 +1932,45 @@ unsigned long __kretprobe_trampoline_han
> > unsigned long trampoline_address,
> > void *frame_pointer)
> > {
> > // ... removed
> > // NULL here
> > + first = node = current->kretprobe_instances.first;
> > + while (node) {
> > + ri = container_of(node, struct kretprobe_instance, llist);
> >
> > - orig_ret_address = (unsigned long)ri->ret_addr;
> > - if (skipped)
> > - pr_warn("%ps must be blacklisted because of incorrect kretprobe order\n",
> > - ri->rp->kp.addr);
> > + BUG_ON(ri->fp != frame_pointer);
> >
> > - if (orig_ret_address != trampoline_address)
> > + orig_ret_address = (unsigned long)ri->ret_addr;
> > + if (orig_ret_address != trampoline_address) {
> > /*
> > * This is the real return address. Any other
> > * instances associated with this task are for
> > * other calls deeper on the call stack
> > */
> > break;
> > + }
> > +
> > + node = node->next;
> > }
> >
>
> Hi, I found a NULL pointer dereference here, where current->kretprobe_instances.first == NULL in these two scenario:
Thanks! that may be what I'm chasing.
>
> 1) In task "rs:main Q:Reg"
> # insmod samples/kprobes/kretprobe_example.ko func=schedule
> # pkill sddm-greeter
>
> 2) In task "llvmpipe-10"
> # insmod samples/kprobes/kretprobe_example.ko func=schedule
> login plasmashell session from sddm graphical interface
OK, schedule function will be the key. I guess the senario is..
1) kretporbe replace the return address with kretprobe_trampoline on task1's kernel stack
2) the task1 forks task2 before returning to the kretprobe_trampoline
3) while copying the process with the kernel stack, task2->kretprobe_instances.first = NULL
4) task2 returns to the kretprobe_trampoline
5) Bomb!
Hmm, we need to fixup the kernel stack when copying process.
Thank you,
>
> based on Masami's v2 + Peter's lockless patch, I'll try the new branch once I can compile kernel
>
> Stacktrace may not be really useful here:
> [ 402.008630] BUG: kernel NULL pointer dereference, address: 0000000000000018
> [ 402.008633] #PF: supervisor read access in kernel mode
> [ 402.008642] #PF: error_code(0x0000) - not-present page
> [ 402.008644] PGD 0 P4D 0
> [ 402.008646] Oops: 0000 [#1] PREEMPT SMP PTI
> [ 402.008649] CPU: 7 PID: 1505 Comm: llvmpipe-10 Kdump: loaded Not tainted 5.9.0-rc2-00111-g72091ec08f03-dirty #45
> [ 402.008650] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/29/2019
> [ 402.008653] RIP: 0010:__kretprobe_trampoline_handler+0xb8/0x17f
> [ 402.008655] Code: 65 4c 8b 34 25 80 6d 01 00 4c 89 e2 48 c7 c7 91 6b 85 91 49 8d b6 38 07 00 00 e8 d1 1a f9 ff 48 85 db 74 06 48 3b 5d d0 75 16 <49> 8b 75 18 48 c7 c7 a0 6c 85 91 48
> 8b 56 28 e8 b2 1a f9 ff 0f 0b
> [ 402.008655] RSP: 0018:ffffab408147bde0 EFLAGS: 00010246
> [ 402.008656] RAX: 0000000000000021 RBX: 0000000000000000 RCX: 0000000000000002
> [ 402.008657] RDX: 0000000080000002 RSI: ffffffff9189757d RDI: 00000000ffffffff
> [ 402.008658] RBP: ffffab408147be20 R08: 0000000000000001 R09: 000000000000955c
> [ 402.008658] R10: 0000000000000004 R11: 0000000000000000 R12: 0000000000000000
> [ 402.008659] R13: 0000000000000000 R14: ffff90736d305f40 R15: 0000000000000000
> [ 402.008661] FS: 00007f20f6ffd700(0000) GS:ffff9073781c0000(0000) knlGS:0000000000000000
> [ 402.008675] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 402.008678] CR2: 0000000000000018 CR3: 00000001ed256006 CR4: 00000000003706e0
> [ 402.008684] Call Trace:
> [ 402.008689] ? elfcorehdr_read+0x40/0x40
> [ 402.008690] ? elfcorehdr_read+0x40/0x40
> [ 402.008691] trampoline_handler+0x42/0x60
> [ 402.008692] kretprobe_trampoline+0x2a/0x50
> [ 402.008693] RIP: 0010:kretprobe_trampoline+0x0/0x50
>
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--
Masami Hiramatsu <mhiramat@xxxxxxxxxx>
