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

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

[Suravee Suthikulpanit]

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@amd.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
---
 arch/x86/kvm/svm.c | 3 +++
 1 file changed, 3 insertions(+)

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
-- 
1.8.3.1

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

[Alex Williamson]

On Fri, 21 Feb 2020 08:52:17 -0600
Suravee Suthikulpanit <suravee.suthikulpanit@amd.com> 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@amd.com>
> Cc: Alex Williamson <alex.williamson@redhat.com>
> ---
>  arch/x86/kvm/svm.c | 3 +++
>  1 file changed, 3 insertions(+)

Works for me, thanks Suravee!

Tested-by: Alex Williamson <alex.williamson@redhat.com>

> 
> 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

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@amd.com> 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@amd.com>
>> Cc: Alex Williamson <alex.williamson@redhat.com>
>> ---
>>  arch/x86/kvm/svm.c | 3 +++
>>  1 file changed, 3 insertions(+)
> 
> Works for me, thanks Suravee!
> 
> Tested-by: Alex Williamson <alex.williamson@redhat.com>
> 
>>
>> 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