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From:   Sasha Levin <sashal@kernel.org>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc:     Steve Rutherford <srutherford@google.com>,
        Jon Cargille <jcargill@google.com>,
        Jim Mattson <jmattson@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sasha Levin <sashal@kernel.org>, kvm@vger.kernel.org
Subject: [PATCH AUTOSEL 5.4 238/330] KVM: Remove CREATE_IRQCHIP/SET_PIT2 race
Date:   Thu, 17 Sep 2020 21:59:38 -0400
Message-Id: <20200918020110.2063155-238-sashal@kernel.org>
In-Reply-To: <20200918020110.2063155-1-sashal@kernel.org>
References: <20200918020110.2063155-1-sashal@kernel.org>
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From: Steve Rutherford <srutherford@google.com>

[ Upstream commit 7289fdb5dcdbc5155b5531529c44105868a762f2 ]

Fixes a NULL pointer dereference, caused by the PIT firing an interrupt
before the interrupt table has been initialized.

SET_PIT2 can race with the creation of the IRQchip. In particular,
if SET_PIT2 is called with a low PIT timer period (after the creation of
the IOAPIC, but before the instantiation of the irq routes), the PIT can
fire an interrupt at an uninitialized table.

Signed-off-by: Steve Rutherford <srutherford@google.com>
Signed-off-by: Jon Cargille <jcargill@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Message-Id: <20200416191152.259434-1-jcargill@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/x86/kvm/x86.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8920ee7b28811..67ad417a29ca4 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5050,10 +5050,13 @@ set_identity_unlock:
 		r = -EFAULT;
 		if (copy_from_user(&u.ps, argp, sizeof(u.ps)))
 			goto out;
+		mutex_lock(&kvm->lock);
 		r = -ENXIO;
 		if (!kvm->arch.vpit)
-			goto out;
+			goto set_pit_out;
 		r = kvm_vm_ioctl_set_pit(kvm, &u.ps);
+set_pit_out:
+		mutex_unlock(&kvm->lock);
 		break;
 	}
 	case KVM_GET_PIT2: {
@@ -5073,10 +5076,13 @@ set_identity_unlock:
 		r = -EFAULT;
 		if (copy_from_user(&u.ps2, argp, sizeof(u.ps2)))
 			goto out;
+		mutex_lock(&kvm->lock);
 		r = -ENXIO;
 		if (!kvm->arch.vpit)
-			goto out;
+			goto set_pit2_out;
 		r = kvm_vm_ioctl_set_pit2(kvm, &u.ps2);
+set_pit2_out:
+		mutex_unlock(&kvm->lock);
 		break;
 	}
 	case KVM_REINJECT_CONTROL: {
-- 
2.25.1