linux-kernel - [PATCH 01/10] KVM: x86: Don't take kvm->lock when iterating over vCPUs in suspend notifier

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250118005552.2626804-2-seanjc@google.com>
Date: Fri, 17 Jan 2025 16:55:43 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, 
	David Woodhouse <dwmw2@...radead.org>, Paul Durrant <paul@....org>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	syzbot+352e553a86e0d75f5120@...kaller.appspotmail.com, 
	Paul Durrant <pdurrant@...zon.com>, David Woodhouse <dwmw@...zon.co.uk>, 
	Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: [PATCH 01/10] KVM: x86: Don't take kvm->lock when iterating over
 vCPUs in suspend notifier

When queueing vCPU PVCLOCK updates in response to SUSPEND or HIBERNATE,
don't take kvm->lock as doing so can trigger a largely theoretical
deadlock, it is perfectly safe to iterate over the xarray of vCPUs without
holding kvm->lock, and kvm->lock doesn't protect kvm_set_guest_paused() in
any way (pv_time.active and pvclock_set_guest_stopped_request are
protected by vcpu->mutex, not kvm->lock).

Reported-by: syzbot+352e553a86e0d75f5120@...kaller.appspotmail.com
Closes: https://lore.kernel.org/all/677c0f36.050a0220.3b3668.0014.GAE@google.com
Fixes: 7d62874f69d7 ("kvm: x86: implement KVM PM-notifier")
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/x86.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b2d9a16fd4d3..26e18c9b0375 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6907,7 +6907,6 @@ static int kvm_arch_suspend_notifier(struct kvm *kvm)
 	unsigned long i;
 	int ret = 0;
 
-	mutex_lock(&kvm->lock);
 	kvm_for_each_vcpu(i, vcpu, kvm) {
 		if (!vcpu->arch.pv_time.active)
 			continue;
@@ -6919,7 +6918,6 @@ static int kvm_arch_suspend_notifier(struct kvm *kvm)
 			break;
 		}
 	}
-	mutex_unlock(&kvm->lock);
 
 	return ret ? NOTIFY_BAD : NOTIFY_DONE;
 }
-- 
2.48.0.rc2.279.g1de40edade-goog