Re: [PATCH] kvm: x86: svm: Fix NULL pointer dereference when AVIC not enabled

[Paolo Bonzini]

On 21/02/20 16:39, Alex Williamson wrote:
> On Fri, 21 Feb 2020 08:52:17 -0600
> Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx> wrote:
> 
>> Launching VM w/ AVIC disabled together with pass-through device
>> results in NULL pointer dereference bug with the following call trace.
>>
>>     RIP: 0010:svm_refresh_apicv_exec_ctrl+0x17e/0x1a0 [kvm_amd]
>>
>>     Call Trace:
>>      kvm_vcpu_update_apicv+0x44/0x60 [kvm]
>>      kvm_arch_vcpu_ioctl_run+0x3f4/0x1c80 [kvm]
>>      kvm_vcpu_ioctl+0x3d8/0x650 [kvm]
>>      do_vfs_ioctl+0xaa/0x660
>>      ? tomoyo_file_ioctl+0x19/0x20
>>      ksys_ioctl+0x67/0x90
>>      __x64_sys_ioctl+0x1a/0x20
>>      do_syscall_64+0x57/0x190
>>      entry_SYSCALL_64_after_hwframe+0x44/0xa9
>>
>> Investigation shows that this is due to the uninitialized usage of
>> struct vapu_svm.ir_list in the svm_set_pi_irte_mode(), which is
>> called from svm_refresh_apicv_exec_ctrl().
>>
>> The ir_list is initialized only if AVIC is enabled. So, fixes by
>> adding a check if AVIC is enabled in the svm_refresh_apicv_exec_ctrl().
>>
>> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=206579
>> Fixes: 8937d762396d ("kvm: x86: svm: Add support to (de)activate posted interrupts.")
>> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
>> Cc: Alex Williamson <alex.williamson@xxxxxxxxxx>
>> ---
>>  arch/x86/kvm/svm.c | 3 +++
>>  1 file changed, 3 insertions(+)
> 
> Works for me, thanks Suravee!
> 
> Tested-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> 
>>
>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>> index 19035fb..1858455 100644
>> --- a/arch/x86/kvm/svm.c
>> +++ b/arch/x86/kvm/svm.c
>> @@ -5222,6 +5222,9 @@ static void svm_refresh_apicv_exec_ctrl(struct kvm_vcpu *vcpu)
>>  	struct vmcb *vmcb = svm->vmcb;
>>  	bool activated = kvm_vcpu_apicv_active(vcpu);
>>  
>> +	if (!avic)
>> +		return;
>> +
>>  	if (activated) {
>>  		/**
>>  		 * During AVIC temporary deactivation, guest could update
> 

Thanks to both of you.  I'll get it to Linus next Monday.

Paolo