From nobody Sat Feb 7 09:58:54 2026 Received: from air.basealt.ru (air.basealt.ru [193.43.8.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0C55133985; Fri, 23 Jan 2026 22:28:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.43.8.18 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769207296; cv=none; b=QoZNJsTFTh9T0C65whZ3lZoIA9gsg6IdKbp8VYU+WQJsWU9++C3YFYXnRlJ5fN8sz53KU8ZtdR/SVb5jfOxzScT6ltYfGbN2pbwo77c8uIQ0L70YP3upgl+NW63mcJC1n0XSzfaEm6jcBZYiXolvmevYdRR1iaeA9/JT7O7w9bw= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769207296; c=relaxed/simple; bh=VWRZeQ56cAdk8X0xitzdlPQGNbd378aNkZE0Bh8Vb64=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=k/RlM+YumA4ifOqe6lRbOUe1mxK3/oDk3C1uRdSCN5HYbGjvpkEvIvYxO/F1L0QoZB27UenO7pIpU71WeV/rBtPIUb/4cxg6ayvZdChAeZLjtz0K/yHv3NTQH8PHsJhfueIQw19a3zC9sM2ZKyKdiAQd8JfmX5FS1BKkYg6Wcsw= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=altlinux.org; spf=pass smtp.mailfrom=altlinux.org; arc=none smtp.client-ip=193.43.8.18 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=altlinux.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=altlinux.org Received: from altlinux.ipa.basealt.ru (unknown [193.43.11.2]) (Authenticated sender: kovalevvv) by air.basealt.ru (Postfix) with ESMTPSA id C56912339E; Sat, 24 Jan 2026 01:28:02 +0300 (MSK) From: Vasiliy Kovalev To: Sean Christopherson , Paolo Bonzini Cc: x86@kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, lvc-project@linuxtesting.org, kovalev@altlinux.org Subject: [PATCH v2] KVM: x86: Add SRCU protection for reading PDPTRs in __get_sregs2() Date: Sat, 24 Jan 2026 01:28:01 +0300 Message-Id: <20260123222801.646123-1-kovalev@altlinux.org> X-Mailer: git-send-email 2.33.8 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Add SRCU read-side protection when reading PDPTR registers in __get_sregs2(). Reading PDPTRs may trigger access to guest memory: kvm_pdptr_read() -> svm_cache_reg() -> load_pdptrs() -> kvm_vcpu_read_guest_page() -> kvm_vcpu_gfn_to_memslot() kvm_vcpu_gfn_to_memslot() dereferences memslots via __kvm_memslots(), which uses srcu_dereference_check() and requires either kvm->srcu or kvm->slots_lock to be held. Currently only vcpu->mutex is held, triggering lockdep warning: =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D WARNING: suspicious RCU usage in kvm_vcpu_gfn_to_memslot 6.12.59+ #3 Not tainted include/linux/kvm_host.h:1062 suspicious rcu_dereference_check() usage! other info that might help us debug this: rcu_scheduler_active =3D 2, debug_locks =3D 1 1 lock held by syz.5.1717/15100: #0: ff1100002f4b00b0 (&vcpu->mutex){+.+.}-{3:3}, at: kvm_vcpu_ioctl+0x1d5/= 0x1590 Call Trace: __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0xf0/0x120 lib/dump_stack.c:120 lockdep_rcu_suspicious+0x1e3/0x270 kernel/locking/lockdep.c:6824 __kvm_memslots include/linux/kvm_host.h:1062 [inline] __kvm_memslots include/linux/kvm_host.h:1059 [inline] kvm_vcpu_memslots include/linux/kvm_host.h:1076 [inline] kvm_vcpu_gfn_to_memslot+0x518/0x5e0 virt/kvm/kvm_main.c:2617 kvm_vcpu_read_guest_page+0x27/0x50 virt/kvm/kvm_main.c:3302 load_pdptrs+0xff/0x4b0 arch/x86/kvm/x86.c:1065 svm_cache_reg+0x1c9/0x230 arch/x86/kvm/svm/svm.c:1688 kvm_pdptr_read arch/x86/kvm/kvm_cache_regs.h:141 [inline] __get_sregs2 arch/x86/kvm/x86.c:11784 [inline] kvm_arch_vcpu_ioctl+0x3e20/0x4aa0 arch/x86/kvm/x86.c:6279 kvm_vcpu_ioctl+0x856/0x1590 virt/kvm/kvm_main.c:4663 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:907 [inline] __se_sys_ioctl fs/ioctl.c:893 [inline] __x64_sys_ioctl+0x18b/0x210 fs/ioctl.c:893 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xbd/0x1d0 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f Found by Linux Verification Center (linuxtesting.org) with Syzkaller. Suggested-by: Sean Christopherson Cc: stable@vger.kernel.org Fixes: 6dba94035203 ("KVM: x86: Introduce KVM_GET_SREGS2 / KVM_SET_SREGS2") Signed-off-by: Vasiliy Kovalev --- v2: Move SRCU lock inside __get_sregs2() as suggested by Sean Christopherson v1: https://lore.kernel.org/all/20260116151523.291892-1-kovalev@altlinux.or= g/ --- arch/x86/kvm/x86.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 8acfdfc583a1..f2aa2986df86 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -12166,9 +12166,11 @@ static void __get_sregs2(struct kvm_vcpu *vcpu, st= ruct kvm_sregs2 *sregs2) return; =20 if (is_pae_paging(vcpu)) { + kvm_vcpu_srcu_read_lock(vcpu); for (i =3D 0 ; i < 4 ; i++) sregs2->pdptrs[i] =3D kvm_pdptr_read(vcpu, i); sregs2->flags |=3D KVM_SREGS2_FLAGS_PDPTRS_VALID; + kvm_vcpu_srcu_read_unlock(vcpu); } } =20 --=20 2.50.1