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

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Date:   Fri, 21 Feb 2020 08:39:34 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        pbonzini@...hat.com, joro@...tes.org, jon.grimm@....com
Subject: Re: [PATCH] kvm: x86: svm: Fix NULL pointer dereference when AVIC
 not enabled

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

Works for me, thanks Suravee!

Tested-by: Alex Williamson <alex.williamson@...hat.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