[SRU][PATCH 1/1] KVM: X86: Fix scan ioapic use-before-initialization

[Colin Ian King]

On 05/12/2018 14:06, Seth Forshee wrote:
> On Tue, Dec 04, 2018 at 12:14:08PM +0100, Juerg Haefliger wrote:
>> On Mon,  3 Dec 2018 21:22:38 -0500
>> Khalid Elmously <khalid.elmously at canonical.com> wrote:
>>
>>> From: Wanpeng Li <wanpengli at tencent.com>
>>>
>>> CVE-2018-19407
>>>
>>> Reported by syzkaller:
>>>
>>>  BUG: unable to handle kernel NULL pointer dereference at 00000000000001c8
>>>  PGD 80000003ec4da067 P4D 80000003ec4da067 PUD 3f7bfa067 PMD 0
>>>  Oops: 0000 [#1] PREEMPT SMP PTI
>>>  CPU: 7 PID: 5059 Comm: debug Tainted: G           OE     4.19.0-rc5 #16
>>>  RIP: 0010:__lock_acquire+0x1a6/0x1990
>>>  Call Trace:
>>>   lock_acquire+0xdb/0x210
>>>   _raw_spin_lock+0x38/0x70
>>>   kvm_ioapic_scan_entry+0x3e/0x110 [kvm]
>>>   vcpu_enter_guest+0x167e/0x1910 [kvm]
>>>   kvm_arch_vcpu_ioctl_run+0x35c/0x610 [kvm]
>>>   kvm_vcpu_ioctl+0x3e9/0x6d0 [kvm]
>>>   do_vfs_ioctl+0xa5/0x690
>>>   ksys_ioctl+0x6d/0x80
>>>   __x64_sys_ioctl+0x1a/0x20
>>>   do_syscall_64+0x83/0x6e0
>>>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
>>>
>>> The reason is that the testcase writes hyperv synic HV_X64_MSR_SINT6 msr
>>> and triggers scan ioapic logic to load synic vectors into EOI exit bitmap.
>>> However, irqchip is not initialized by this simple testcase, ioapic/apic
>>> objects should not be accessed.
>>> This can be triggered by the following program:
>>>
>>>     #define _GNU_SOURCE
>>>
>>>     #include <endian.h>
>>>     #include <stdint.h>
>>>     #include <stdio.h>
>>>     #include <stdlib.h>
>>>     #include <string.h>
>>>     #include <sys/syscall.h>
>>>     #include <sys/types.h>
>>>     #include <unistd.h>
>>>
>>>     uint64_t r[3] = {0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffffff};
>>>
>>>     int main(void)
>>>     {
>>>     	syscall(__NR_mmap, 0x20000000, 0x1000000, 3, 0x32, -1, 0);
>>>     	long res = 0;
>>>     	memcpy((void*)0x20000040, "/dev/kvm", 9);
>>>     	res = syscall(__NR_openat, 0xffffffffffffff9c, 0x20000040, 0, 0);
>>>     	if (res != -1)
>>>     		r[0] = res;
>>>     	res = syscall(__NR_ioctl, r[0], 0xae01, 0);
>>>     	if (res != -1)
>>>     		r[1] = res;
>>>     	res = syscall(__NR_ioctl, r[1], 0xae41, 0);
>>>     	if (res != -1)
>>>     		r[2] = res;
>>>     	memcpy(
>>>     			(void*)0x20000080,
>>>     			"\x01\x00\x00\x00\x00\x5b\x61\xbb\x96\x00\x00\x40\x00\x00\x00\x00\x01\x00"
>>>     			"\x08\x00\x00\x00\x00\x00\x0b\x77\xd1\x78\x4d\xd8\x3a\xed\xb1\x5c\x2e\x43"
>>>     			"\xaa\x43\x39\xd6\xff\xf5\xf0\xa8\x98\xf2\x3e\x37\x29\x89\xde\x88\xc6\x33"
>>>     			"\xfc\x2a\xdb\xb7\xe1\x4c\xac\x28\x61\x7b\x9c\xa9\xbc\x0d\xa0\x63\xfe\xfe"
>>>     			"\xe8\x75\xde\xdd\x19\x38\xdc\x34\xf5\xec\x05\xfd\xeb\x5d\xed\x2e\xaf\x22"
>>>     			"\xfa\xab\xb7\xe4\x42\x67\xd0\xaf\x06\x1c\x6a\x35\x67\x10\x55\xcb",
>>>     			106);
>>>     	syscall(__NR_ioctl, r[2], 0x4008ae89, 0x20000080);
>>>     	syscall(__NR_ioctl, r[2], 0xae80, 0);
>>>     	return 0;
>>>     }
>>>
>>> This patch fixes it by bailing out scan ioapic if ioapic is not initialized in
>>> kernel.
>>>
>>> Reported-by: Wei Wu <ww9210 at gmail.com>
>>> Cc: Paolo Bonzini <pbonzini at redhat.com>
>>> Cc: Radim Krčmář <rkrcmar at redhat.com>
>>> Cc: Wei Wu <ww9210 at gmail.com>
>>> Signed-off-by: Wanpeng Li <wanpengli at tencent.com>
>>> Cc: stable at vger.kernel.org
>>> Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>
>>
>> Empty line here please.
> 
> Um, why? This has never been a requirement, and it's not what is
> produced by 'git cherry-pick -x'. I personally don't want to have to go
> in and hand-edit the commit message to add a blank line here every time
> I cherry pick a patch.

+1 to that too, we've never added blank lines in the past, why the change?

Colin