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

[Stefan Bader]

On 18.12.18 13:37, Kleber Souza wrote:
> On 12/4/18 3:22 AM, Khalid Elmously 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>
>> (cherry-picked from e97f852fd4561e77721bb9a4e0ea9d98305b1e93)
> (cherry picked from commit e97f852fd4561e77721bb9a4e0ea9d98305b1e93)
>> Signed-off-by: Khalid Elmously <khalid.elmously at canonical.com>
> 
> With the cherry-pick line above fixed:
> 
> Acked-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>
Acked-by: Stefan Bader <stefan.bader at canonical.com>
> 
>> ---

+1 to fix cherry pick line.

>>  arch/x86/kvm/x86.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index c98ffb0e6b47..a3b6f780ad99 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -7225,7 +7225,8 @@ static void vcpu_scan_ioapic(struct kvm_vcpu *vcpu)
>>  	else {
>>  		if (vcpu->arch.apicv_active)
>>  			kvm_x86_ops->sync_pir_to_irr(vcpu);
>> -		kvm_ioapic_scan_entry(vcpu, vcpu->arch.ioapic_handled_vectors);
>> +		if (ioapic_in_kernel(vcpu->kvm))
>> +			kvm_ioapic_scan_entry(vcpu, vcpu->arch.ioapic_handled_vectors);
>>  	}
>>  
>>  	if (is_guest_mode(vcpu))
> 
> 
> 


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