kvm: WARNING in kvm_apic_accept_events

[Dmitry Vyukov]

Hello,

The following program triggers WARNING in kvm_apic_accept_events:

// autogenerated by syzkaller (http://github.com/google/syzkaller)
#include <unistd.h>
#include <sys/syscall.h>
#include <string.h>
#include <stdint.h>

long r[32];

int main()
{
        memset(r, -1, sizeof(r));
        r[0] = syscall(SYS_mmap, 0x20000000ul, 0x10000ul, 0x3ul,
0x32ul, 0xfffffffffffffffful, 0x0ul);
        memcpy((void*)0x20007000, "\x2f\x64\x65\x76\x2f\x6b\x76\x6d", 8);
        r[2] = syscall(SYS_open, 0x20007000ul, 0x801ul, 0x0ul, 0, 0, 0);
        r[3] = syscall(SYS_ioctl, r[2], 0xae01ul, 0x0ul, 0, 0, 0);
        *(uint64_t*)0x2000cbe8 = (uint64_t)0x2cf6;
        r[5] = syscall(SYS_ioctl, r[3], 0xae78ul, 0x2000cbe8ul, 0, 0, 0);
        r[6] = syscall(SYS_ioctl, r[2], 0xae01ul, 0x0ul, 0, 0, 0);
        r[7] = syscall(SYS_ioctl, r[6], 0xae60ul, 0, 0, 0, 0);
        r[8] = syscall(SYS_ioctl, r[6], 0xae41ul, 0x0ul, 0, 0, 0);
        *(uint8_t*)0x20001f89 = (uint8_t)0xff5b;
        *(uint8_t*)0x20001f8a = (uint8_t)0x8;
        *(uint8_t*)0x20001f8b = (uint8_t)0x7;
        *(uint8_t*)0x20001f8c = (uint8_t)0x8;
        *(uint32_t*)0x20001f8d = (uint32_t)0x2;
        *(uint8_t*)0x20001f91 = (uint8_t)0xfffffffffffffff7;
        *(uint8_t*)0x20001f92 = (uint8_t)0x8;
        *(uint8_t*)0x20001f93 = (uint8_t)0x6;
        *(uint8_t*)0x20001f94 = (uint8_t)0x4e399187;
        *(uint8_t*)0x20001f95 = (uint8_t)0x28;
        *(uint8_t*)0x20001f96 = (uint8_t)0x5;
        *(uint8_t*)0x20001f97 = (uint8_t)0x7;
        *(uint8_t*)0x20001f98 = (uint8_t)0x4;
        *(uint32_t*)0x20001f99 = (uint32_t)0x4;
        *(uint32_t*)0x20001f9d = (uint32_t)0x8;
        *(uint8_t*)0x20001fa1 = (uint8_t)0x1;
        *(uint8_t*)0x20001fa2 = (uint8_t)0x4;
        *(uint8_t*)0x20001fa3 = (uint8_t)0x2;
        *(uint8_t*)0x20001fa4 = (uint8_t)0x5;
        r[28] = syscall(SYS_ioctl, r[8], 0x4040aea0ul, 0x20001f89ul, 0, 0, 0);
        *(uint32_t*)0x2000c000 = (uint32_t)0x2;
        r[30] = syscall(SYS_ioctl, r[8], 0x4004ae99ul, 0x2000c000ul, 0, 0, 0);
        r[31] = syscall(SYS_ioctl, r[8], 0xae80ul, 0, 0, 0, 0);
        return 0;
}


------------[ cut here ]------------
WARNING: CPU: 1 PID: 6658 at arch/x86/kvm/lapic.c:2157
kvm_apic_accept_events+0x3dd/0x440()
Modules linked in:
CPU: 1 PID: 6658 Comm: a.out Tainted: G        W       4.4.0-rc8+ #216
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
 00000000ffffffff ffff88006c8bf990 ffffffff82904c8d 0000000000000000
 ffff8800624eaf00 ffffffff85ee24a0 ffff88006c8bf9d0 ffffffff8133e979
 ffffffff810d4f0d ffffffff85ee24a0 000000000000086d ffff88006571b608
Call Trace:
 [<     inline     >] __dump_stack lib/dump_stack.c:15
 [<ffffffff82904c8d>] dump_stack+0x6f/0xa2 lib/dump_stack.c:50
 [<ffffffff8133e979>] warn_slowpath_common+0xd9/0x140 kernel/panic.c:460
 [<ffffffff8133eba9>] warn_slowpath_null+0x29/0x30 kernel/panic.c:493
 [<ffffffff810d4f0d>] kvm_apic_accept_events+0x3dd/0x440
arch/x86/kvm/lapic.c:2157
 [<     inline     >] vcpu_block arch/x86/kvm/x86.c:6627
 [<     inline     >] vcpu_run arch/x86/kvm/x86.c:6662
 [<ffffffff81068822>] kvm_arch_vcpu_ioctl_run+0xc32/0x5820
arch/x86/kvm/x86.c:6818
 [<ffffffff8101cf61>] kvm_vcpu_ioctl+0x5f1/0xd00
arch/x86/kvm/../../../virt/kvm/kvm_main.c:2375
 [<     inline     >] vfs_ioctl fs/ioctl.c:43
 [<ffffffff817b36b1>] do_vfs_ioctl+0x681/0xe40 fs/ioctl.c:607
 [<     inline     >] SYSC_ioctl fs/ioctl.c:622
 [<ffffffff817b3eff>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:613
 [<ffffffff85e745b6>] entry_SYSCALL_64_fastpath+0x16/0x7a
arch/x86/entry/entry_64.S:185
---[ end trace 231a97373e5bf4b0 ]---


On commit b06f3a168cdcd80026276898fd1fee443ef25743 (Jan 6).