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

[Stefan Bader]

On 05.12.18 15:10, Colin Ian King wrote:
> 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
> 
I did in some cases but would not make that a strict requirement in general. It
helps to improve separating the signed off chain from upstream from those added
by us.

-Stefan

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