Re: NULL-ptr deref in kvm_arch_vcpu_ioctl under AMD CPUs

[Robert ÅwiÄcki]

> ====
> // autogenerated by syzkaller (http://github.com/google/syzkaller)
> #include <unistd.h>
> #include <sys/syscall.h>
> #include <string.h>
> #include <stdint.h>
> #include <pthread.h>
>
> long r[6];
>
> int main()
> {
> memset(r, -1, sizeof(r));
> r[0] = syscall(SYS_mmap, 0x20000000ul, 0x13000ul, 0x3ul, 0x32ul,
> 0xfffffffffffffffful, 0x0ul);
> memcpy((void*)0x2000eedb, "\x2f\x64\x65\x76\x2f\x6b\x76\x6d", 8);
> r[2] = syscall(SYS_open, 0x2000eedbul, 0x0ul, 0x100ul, 0, 0, 0);
> r[3] = syscall(SYS_ioctl, r[2], 0xae01ul, 0x0ul, 0, 0, 0);
> r[4] = syscall(SYS_ioctl, r[3], 0xae41ul, 0x7ul, 0, 0, 0);
> r[5] = syscall(SYS_ioctl, r[4], 0x8040ae9ful, 0x20010feful, 0, 0, 0);
> return 0;
> }
> ====
>
> strace:
>
> open("/dev/kvm", O_RDONLY)              = 3
> ioctl(3, KVM_CREATE_VM, 0)              = 4
> ioctl(4, KVM_CREATE_VCPU, 0x7)          = 5
> ioctl(5, KVM_GET_PIT2 or KVM_GET_VCPU_EVENTS, 0x20010fef) = 0
>
> Should be run in parallel (try increasing 10 to 100 or so, if this doesn't work)
>
> $ for x in `seq 1 10`; do { ./prog & }; done

Here's a very similar one, but it works *inside* qemu, with nested
virtualization enabled (AMD SVM). It hits another symbol in the
kernel, but the general idea is the same. Run this binary ~100 times
in parallel. Tested with host: 4.4 and guest 4.4 and 4.5-rc4 on host
CPU Opteron 6272

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

#ifndef SYS_mmap
#define SYS_mmap 9
#endif
#ifndef SYS_syz_open_dev
#define SYS_syz_open_dev 1000001
#endif
#ifndef SYS_ioctl
#define SYS_ioctl 16
#endif

long r[6];

int main()
{
memset(r, -1, sizeof(r));
r[0] = syscall(SYS_mmap, 0x20000000ul, 0xf000ul, 0x3ul, 0x32ul,
0xfffffffffffffffful, 0x0ul);
memcpy((void*)0x2000173f, "\x2f\x64\x65\x76\x2f\x6b\x76\x6d", 8);
r[2] = syscall(SYS_open, 0x2000173ful, 0x0ul, 0x100ul, 0, 0, 0);
r[3] = syscall(SYS_ioctl, r[2], 0xae01ul, 0x0ul, 0, 0, 0);
r[4] = syscall(SYS_ioctl, r[3], 0xae41ul, 0x8ul, 0, 0, 0);
r[5] = syscall(SYS_ioctl, r[4], 0x8004ae98ul, 0x20007000ul, 0, 0, 0);
return 0;
}
=================

strace:
open("/dev/kvm", O_RDONLY)              = 3
ioctl(3, KVM_CREATE_VM, 0)              = 4
ioctl(4, KVM_CREATE_VCPU, 0x8)          = 5
ioctl(5, KVM_GET_MP_STATE, 0x20007000)  = 0

Run as: for x in `seq 1 40`; do { ./prog & }; done

[  162.697592] kvm: Nested Virtualization enabled
[  218.733272] BUG: unable to handle kernel NULL pointer dereference
at 00000000000000f0
[  218.733309] IP: [<ffffffffa025e34a>] kvm_apic_accept_events+0x2a/0x150 [kvm]
[  218.733312] PGD d4a1067 PUD f7b8067 PMD 0
[  218.733314] Oops: 0000 [#1] SMP
[  218.733325] Modules linked in: kvm_amd kvm ext4 crc16 mbcache jbd2
sg sr_mod cdrom sd_mod ata_generic uhci_hcd ehci_hcd ata_piix usbcore
e1000 libata usb_common scsi_mod floppy
[  218.733328] CPU: 1 PID: 2106 Comm: y Not tainted
4.3.0-0.bpo.1-amd64 #1 Debian 4.3.3-7~bpo8+1
[  218.733329] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS 1.7.5-20140531_083030-gandalf 04/01/2014
[  218.733330] task: ffff88001f97e3c0 ti: ffff88001f9c8000 task.ti:
ffff88001f9c8000
[  218.733351] RIP: 0010:[<ffffffffa025e34a>]  [<ffffffffa025e34a>]
kvm_apic_accept_events+0x2a/0x150 [kvm]
[  218.733353] RSP: 0018:ffff88001f9cbdf0  EFLAGS: 00010246
[  218.733354] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000100000000
[  218.733355] RDX: ffff88000da65000 RSI: ffff88001f9cbe30 RDI: ffff88000ea18100
[  218.733356] RBP: ffff88000ea18100 R08: 0000000000000000 R09: 0000000000000000
[  218.733357] R10: 0000000000000000 R11: 0000000000000203 R12: 000000008004ae98
[  218.733358] R13: 0000000020007000 R14: ffff88000d48bb00 R15: 0000000020007000
[  218.733362] FS:  00007fb33aba2700(0000) GS:ffff88000f900000(0000)
knlGS:0000000000000000
[  218.733363] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  218.733365] CR2: 00000000000000f0 CR3: 000000000f7bb000 CR4: 00000000000006e0
[  218.733369] Stack:
[  218.733372]  ffff88000ea18100 00000000a9f3a679 ffff88000ea18100
ffff88001f9cbe30
[  218.733374]  ffffffffa0240172 ffffffffffffffea ffff88000ea18100
ffffffffa022c63c
[  218.733376]  ffff88000ea14000 ffffffff8121705b ffff88000ea14000
ffff88000ea14a30
[  218.733377] Call Trace:
[  218.733396]  [<ffffffffa0240172>] ?
kvm_arch_vcpu_ioctl_get_mpstate+0x12/0x40 [kvm]
[  218.733410]  [<ffffffffa022c63c>] ? kvm_vcpu_ioctl+0xfc/0x5a0 [kvm]
[  218.733414]  [<ffffffff8121705b>] ? anon_inode_getfd+0x4b/0x70
[  218.733427]  [<ffffffffa022b70f>] ? kvm_dev_ioctl+0x11f/0x450 [kvm]
[  218.733432]  [<ffffffff811e3255>] ? do_vfs_ioctl+0x2d5/0x4b0
[  218.733435]  [<ffffffff811e34a6>] ? SyS_ioctl+0x76/0x90
[  218.733439]  [<ffffffff8158a3f6>] ? system_call_fast_compare_end+0xc/0x6b
[  218.733460] Code: 00 66 66 66 66 90 55 53 48 89 fd 48 83 ec 10 48
8b 9f a0 02 00 00 65 48 8b 04 25 28 00 00 00 48 89 44 24 08 31 c0 66
66 66 66 90 <48> 83 bb f0 00 00 00 00 75 22 48 8b 44 24 08 65 48 33 04
25 28

-- 
Robert ÅwiÄcki