Hi all,
I've hit the following while fuzzing with syzkaller inside a KVM tools guest
running the latest -next kernel:
[ 326.963405] general protection fault: 0000 [#1] PREEMPT SMP KASAN
[ 326.963416] Modules linked in:
[ 326.963430] CPU: 0 PID: 10488 Comm: syz-executor Not tainted 4.6.0-rc3-next-20160412-sasha-00023-g0b02d6d-dirty #2998
[ 326.963437] task: ffff8800b6f91000 ti: ffff8801b5de0000 task.ti: ffff8801b5de0000
[ 326.963501] RIP: free_pages_and_swap_cache (./arch/x86/include/asm/bitops.h:311 (discriminator 3) include/linux/page-flags.h:320 (discriminator 3) mm/swap_state.c:242 (discriminator 3) mm/swap_state.c:269 (discriminator 3))
[ 326.963505] RSP: 0018:ffff8801b5de7878 EFLAGS: 00010202
[ 326.963510] RAX: 00000000000015b0 RBX: 0000000000000003 RCX: 0000000000000000
[ 326.963514] RDX: 0000000000000001 RSI: 0000000000000000 RDI: ffffffffb989fa00
[ 326.963519] RBP: ffff8801b5de78b0 R08: 0000000000000000 R09: fffffffffffffff4
[ 326.963524] R10: 000000000014000a R11: ffffffffaa24a300 R12: dffffc0000000000
[ 326.963532] R13: 000000000000ad80 R14: ffff8800b5eef010 R15: 000000000000ad80
[ 326.963539] FS: 00007f01f5466700(0000) GS:ffff8801d4200000(0000) knlGS:0000000000000000
[ 326.963544] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 326.963549] CR2: 0000000000811000 CR3: 00000001b3c49000 CR4: 00000000000406f0
[ 326.963556] Stack:
[ 326.963566] ffff8801b5de7958 000001fe3911bddd ffff8800b5eef000 dffffc0000000000
[ 326.963574] ffff8800b5eef008 ffff8801b5de7958 00000000000001fe ffff8801b5de78f0
[ 326.963582] ffffffffa06d6ce7 ffff8801b5de7980 ffff8801b5bcc828 dffffc0000000000
[ 326.963583] Call Trace:
[ 326.963596] tlb_flush_mmu_free (mm/memory.c:259 (discriminator 4))
[ 326.963604] tlb_finish_mmu (mm/memory.c:283)
[ 326.963613] exit_mmap (mm/mmap.c:2730)
[ 326.963649] mmput (include/linux/compiler.h:222 kernel/fork.c:748 kernel/fork.c:715)
[ 326.963687] do_exit (./arch/x86/include/asm/bitops.h:311 include/linux/thread_info.h:92 kernel/exit.c:437 kernel/exit.c:735)
[ 326.963712] do_group_exit (kernel/exit.c:862)
[ 326.963720] get_signal (kernel/signal.c:2307)
[ 326.963735] do_signal (arch/x86/kernel/signal.c:784)
[ 326.963859] exit_to_usermode_loop (arch/x86/entry/common.c:231)
[ 326.963868] syscall_return_slowpath (arch/x86/entry/common.c:274 arch/x86/entry/common.c:329)
[ 326.963877] ret_from_fork (arch/x86/entry/entry_64.S:404)
[ 326.963953] Code: 00 74 08 4c 89 ff e8 c5 88 05 00 4d 8b 2f 4d 85 ed 4d 89 ef 75 0e 31 f6 48 c7 c7 c0 58 56 ae e8 58 c6 99 01 4c 89 e8 48 c1 e8 03 <42> 80 3c 20 00 74 08 4c 89 ef e8 96 88 05 00 49 8b 45 00 f6 c4
All code
========
0: 00 74 08 4c add %dh,0x4c(%rax,%rcx,1)
4: 89 ff mov %edi,%edi
6: e8 c5 88 05 00 callq 0x588d0
b: 4d 8b 2f mov (%r15),%r13
e: 4d 85 ed test %r13,%r13
11: 4d 89 ef mov %r13,%r15
14: 75 0e jne 0x24
16: 31 f6 xor %esi,%esi
18: 48 c7 c7 c0 58 56 ae mov $0xffffffffae5658c0,%rdi
1f: e8 58 c6 99 01 callq 0x199c67c
24: 4c 89 e8 mov %r13,%rax
27: 48 c1 e8 03 shr $0x3,%rax
2b:* 42 80 3c 20 00 cmpb $0x0,(%rax,%r12,1) <-- trapping instruction
30: 74 08 je 0x3a
32: 4c 89 ef mov %r13,%rdi
35: e8 96 88 05 00 callq 0x588d0
3a: 49 8b 45 00 mov 0x0(%r13),%rax
3e: f6 c4 00 test $0x0,%ah
Code starting with the faulting instruction
===========================================
0: 42 80 3c 20 00 cmpb $0x0,(%rax,%r12,1)
5: 74 08 je 0xf
7: 4c 89 ef mov %r13,%rdi
a: e8 96 88 05 00 callq 0x588a5
f: 49 8b 45 00 mov 0x0(%r13),%rax
13: f6 c4 00 test $0x0,%ah
[ 326.963963] RIP free_pages_and_swap_cache (./arch/x86/include/asm/bitops.h:311 (discriminator 3) include/linux/page-flags.h:320 (discriminator 3) mm/swap_state.c:242 (discriminator 3) mm/swap_state.c:269 (discriminator 3))
[ 326.963965] RSP <ffff8801b5de7878>