Re: WARNING in arch_uprobe_analyze_insn

[Oleg Nesterov <oleg@redhat.com>]

On 05/14, syzbot wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    66e1c94db3cd Merge branch 'x86-pti-for-linus' of git://git..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=11817107800000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=fcce42b221691ff9
> dashboard link: https://syzkaller.appspot.com/bug?extid=30d675e3ca03c1c351e7
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=143d5417800000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11178e97800000

doesn't work for me...

I guess syscall(__NR_perf_event_open) should trigger perf_uprobe_init() but
the hard-coded attr.type doesn't match perf_uprobe->type on my machine...


Nevermind, it seems that the code is indeed wrong, uprobe_init_insn() does

	insn_init(insn, auprobe->insn, sizeof(auprobe->insn), x86_64);
	/* has the side-effect of processing the entire instruction */
	insn_get_length(insn);
	if (WARN_ON_ONCE(!insn_complete(insn)))
		return -ENOEXEC;

Masami, could your help?

What if insn can't be decoded, say, because it is not valid? Can't
insn_complete() return F in this case?

I think it can... Say, insn_get_immediate() doesn't set immediate.got in
err_out path.

Unfortunately, insn_get_length() returns void, and I do not see any
insn-was-decoded-correctly helper. Perhaps we should simply remove
this WARN_ON() ?

Alternatively, If am right we can move this check down after the "good_insns"
checks, but this doesn't look very clean to me.


> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+30d675e3ca03c1c351e7@syzkaller.appspotmail.com
> 
> random: sshd: uninitialized urandom read (32 bytes read)
> random: sshd: uninitialized urandom read (32 bytes read)
> random: sshd: uninitialized urandom read (32 bytes read)
> random: sshd: uninitialized urandom read (32 bytes read)
> random: sshd: uninitialized urandom read (32 bytes read)
> WARNING: CPU: 0 PID: 4511 at arch/x86/kernel/uprobes.c:296 insn_complete
> arch/x86/include/asm/insn.h:147 [inline]
> WARNING: CPU: 0 PID: 4511 at arch/x86/kernel/uprobes.c:296 uprobe_init_insn
> arch/x86/kernel/uprobes.c:296 [inline]
> WARNING: CPU: 0 PID: 4511 at arch/x86/kernel/uprobes.c:296
> arch_uprobe_analyze_insn+0x13d/0x15f0 arch/x86/kernel/uprobes.c:861
> Kernel panic - not syncing: panic_on_warn set ...
> 
> CPU: 0 PID: 4511 Comm: syz-executor347 Not tainted 4.17.0-rc4+ #46
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x1b9/0x294 lib/dump_stack.c:113
>  panic+0x22f/0x4de kernel/panic.c:184
>  __warn.cold.8+0x163/0x1b3 kernel/panic.c:536
>  report_bug+0x252/0x2d0 lib/bug.c:186
>  fixup_bug arch/x86/kernel/traps.c:178 [inline]
>  do_error_trap+0x1de/0x490 arch/x86/kernel/traps.c:296
>  do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:315
>  invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:992
> RIP: 0010:insn_complete arch/x86/include/asm/insn.h:147 [inline]
> RIP: 0010:uprobe_init_insn arch/x86/kernel/uprobes.c:296 [inline]
> RIP: 0010:arch_uprobe_analyze_insn+0x13d/0x15f0
> arch/x86/kernel/uprobes.c:861
> RSP: 0018:ffff8801cf277510 EFLAGS: 00010246
> RAX: 0000000000000000 RBX: ffff8801cf277560 RCX: ffffffff876ccf2a
> RDX: 0000000000000004 RSI: ffffffff876ce6ab RDI: ffff8801cf27759c
> RBP: ffff8801cf277628 R08: ffff8801d8c0a5c0 R09: ffff8801cf277560
> R10: ffff8801d7ad81d0 R11: ffff8801cf2775af R12: 0000000000000000
> R13: dffffc0000000000 R14: ffff8801d7ad8080 R15: ffff8801cf277600
>  prepare_uprobe kernel/events/uprobes.c:610 [inline]
>  install_breakpoint.isra.21+0x710/0x830 kernel/events/uprobes.c:657
>  uprobe_mmap+0x6a0/0xcf0 kernel/events/uprobes.c:1089
>  mmap_region+0x5c8/0x1870 mm/mmap.c:1807
>  do_mmap+0xde2/0x1360 mm/mmap.c:1535
>  do_mmap_pgoff include/linux/mm.h:2237 [inline]
>  vm_mmap_pgoff+0x1fb/0x2a0 mm/util.c:357
>  ksys_mmap_pgoff+0x4c9/0x640 mm/mmap.c:1585
>  __do_sys_mmap arch/x86/kernel/sys_x86_64.c:100 [inline]
>  __se_sys_mmap arch/x86/kernel/sys_x86_64.c:91 [inline]
>  __x64_sys_mmap+0xe9/0x1b0 arch/x86/kernel/sys_x86_64.c:91
>  do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x43ff29
> RSP: 002b:00007ffc922a4898 EFLAGS: 00000212 ORIG_RAX: 0000000000000009
> RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 000000000043ff29
> RDX: 0000000000000000 RSI: 0000000000002000 RDI: 000000002000c000
> RBP: 00000000006ca018 R08: 0000000000000003 R09: 0000000000000000
> R10: 0000000000000012 R11: 0000000000000212 R12: 0000000000401850
> R13: 00000000004018e0 R14: 0000000000000000 R15: 0000000000000000
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> Kernel Offset: disabled
> Rebooting in 86400 seconds..
> 
> 
> ---
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