Re: [PATCH v3 5/6] KVM: arm64: vgic-v3: Retire all pending LPIs on vcpu destroy

From: James Morse <james.morse@arm.com>
To: Marc Zyngier <maz@kernel.org>, Zenghui Yu <yuzenghui@huawei.com>
Cc: Julien Grall <julien@xen.org>,
	kvm@vger.kernel.org, Andre Przywara <Andre.Przywara@arm.com>,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v3 5/6] KVM: arm64: vgic-v3: Retire all pending LPIs on vcpu destroy
Date: Thu, 23 Apr 2020 12:35:30 +0100	[thread overview]
Message-ID: <2a0d1542-1964-c818-aae8-76f9227676b8@arm.com> (raw)
In-Reply-To: <20200422161844.3848063-6-maz@kernel.org>

Hi Marc, Zenghui,

On 22/04/2020 17:18, Marc Zyngier wrote:
> From: Zenghui Yu <yuzenghui@huawei.com>
> 
> It's likely that the vcpu fails to handle all virtual interrupts if
> userspace decides to destroy it, leaving the pending ones stay in the
> ap_list. If the un-handled one is a LPI, its vgic_irq structure will
> be eventually leaked because of an extra refcount increment in
> vgic_queue_irq_unlock().

> diff --git a/virt/kvm/arm/vgic/vgic-init.c b/virt/kvm/arm/vgic/vgic-init.c
> index a963b9d766b73..53ec9b9d9bc43 100644
> --- a/virt/kvm/arm/vgic/vgic-init.c
> +++ b/virt/kvm/arm/vgic/vgic-init.c
> @@ -348,6 +348,12 @@ void kvm_vgic_vcpu_destroy(struct kvm_vcpu *vcpu)
>  {
>  	struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
>  
> +	/*
> +	 * Retire all pending LPIs on this vcpu anyway as we're
> +	 * going to destroy it.
> +	 */

Looking at the other caller, do we need something like:
|	if (vgic_cpu->lpis_enabled)

?

> +	vgic_flush_pending_lpis(vcpu);
> +

Otherwise, I get this on a gic-v2 machine!:
[ 1742.187139] BUG: KASAN: use-after-free in vgic_flush_pending_lpis+0x250/0x2c0
[ 1742.194302] Read of size 8 at addr ffff0008e1bf1f28 by task qemu-system-aar/542
[ 1742.203140] CPU: 2 PID: 542 Comm: qemu-system-aar Not tainted
5.7.0-rc2-00006-g4fb0f7bb0e27 #2
[ 1742.211780] Hardware name: ARM LTD ARM Juno Development Platform/ARM Juno Development
Platform, BIOS EDK II Jul 30 2018
[ 1742.222596] Call trace:
[ 1742.225059]  dump_backtrace+0x0/0x328
[ 1742.228738]  show_stack+0x18/0x28
[ 1742.232071]  dump_stack+0x134/0x1b0
[ 1742.235578]  print_address_description.isra.0+0x6c/0x350
[ 1742.240910]  __kasan_report+0x10c/0x180
[ 1742.244763]  kasan_report+0x4c/0x68
[ 1742.248268]  __asan_report_load8_noabort+0x30/0x48
[ 1742.253081]  vgic_flush_pending_lpis+0x250/0x2c0
[ 1742.257718]  __kvm_vgic_destroy+0x1cc/0x478
[ 1742.261919]  kvm_vgic_destroy+0x30/0x48
[ 1742.265773]  kvm_arch_destroy_vm+0x20/0x128
[ 1742.269976]  kvm_put_kvm+0x3e0/0x8d0
[ 1742.273567]  kvm_vm_release+0x3c/0x60
[ 1742.277248]  __fput+0x218/0x630
[ 1742.280406]  ____fput+0x10/0x20
[ 1742.283565]  task_work_run+0xd8/0x1f0
[ 1742.287245]  do_exit+0x87c/0x2640
[ 1742.290575]  do_group_exit+0xd0/0x258
[ 1742.294254]  __arm64_sys_exit_group+0x3c/0x48
[ 1742.298631]  el0_svc_common.constprop.0+0x10c/0x348
[ 1742.303529]  do_el0_svc+0x48/0xd0
[ 1742.306861]  el0_sync_handler+0x11c/0x1b8
[ 1742.310888]  el0_sync+0x158/0x180
[ 1742.315716] The buggy address belongs to the page:
[ 1742.320529] page:fffffe002366fc40 refcount:0 mapcount:0 mapping:000000007e21d29f index:0x0
[ 1742.328821] flags: 0x2ffff00000000000()
[ 1742.332678] raw: 2ffff00000000000 0000000000000000 ffffffff23660401 0000000000000000
[ 1742.340449] raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
[ 1742.348215] page dumped because: kasan: bad access detected
[ 1742.355304] Memory state around the buggy address:
[ 1742.360115]  ffff0008e1bf1e00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[ 1742.367360]  ffff0008e1bf1e80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[ 1742.374606] >ffff0008e1bf1f00: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[ 1742.381851]                                   ^
[ 1742.386399]  ffff0008e1bf1f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[ 1742.393645]  ffff0008e1bf2000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
[ 1742.400889] ==================================================================
[ 1742.408132] Disabling lock debugging due to kernel taint

With that:
Reviewed-by: James Morse <james.morse@arm.com>

Thanks,

James
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