From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-f201.google.com (mail-pf1-f201.google.com [209.85.210.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2F817213254 for ; Tue, 2 Dec 2025 02:03:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764641020; cv=none; b=NY81Wj5Yi1njLLrqRYrH5htit4ujzK+3TUSWoNkQsr/j0myOocX38gfLHjFrgBkQSacPuzXKMqQ0zt9E2/npk7TYuG22gH0v++Wgg3dh2EJlQEmph7vfGw4+TBK3ERGJI1xtoHZLmZ8PawSEkmYX366t2Ie4z/aInOYoK464t3g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764641020; c=relaxed/simple; bh=hg+dKOfYTC+Pd8pCiItqJSzZxpkF+UZ63xbDGe51t14=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=Nq2el/FUs1nQcEWmj17Jg0T0abwovSqaG/AgYq+EBB1GKYGLD867kNXMYankBgTKmgPqPCeWoeDdQD3mjuKVF13WaVTp8oCitX900/Mvrliy0HLWqf8sEaQ8P0IyOIww3r+5F7KXGzA2YOm4fXT73IKMIi5bSFQCd4BDhoma+8A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=Yv8py3VZ; arc=none smtp.client-ip=209.85.210.201 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="Yv8py3VZ" Received: by mail-pf1-f201.google.com with SMTP id d2e1a72fcca58-7c240728e2aso8828474b3a.3 for ; Mon, 01 Dec 2025 18:03:38 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1764641018; x=1765245818; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:from:to:cc:subject:date:message-id:reply-to; bh=BPeQZ43Hcfmq7Td8KMLsolI+fW6jW5ccnQO0u+Kn36Y=; b=Yv8py3VZxuq+R5vgdZopnoXb7wmj4ue0GoPsIWroWPgSrJeGwMxvldDPEaTqMlghg9 Av47KpoiNzIV6TXcmF7wf9q489BNwlNGIc1DQ9+fUY0EjH9+cPVNj6OHdwkYVGmDoXRV MCYs8T/JPVjutMgPGpEaTjVPmurYvpC8wSwCfeRkr4kBUxbtxKFshtloiYF92PY7VAXp t9oKkGIOIFEenB4jyCtOTf+C4ceyRfA8Xk+eSeAuTv92aRLrGyK5Kk575v02qCZpcFtV 8ftK0HRTKnrDt/UGqrRMQVElkRQClVnL/PGRr99cF7Zi9jZi+2+W5TTJC4x6j7+OwkgA bKnA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1764641018; x=1765245818; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=BPeQZ43Hcfmq7Td8KMLsolI+fW6jW5ccnQO0u+Kn36Y=; b=tVEFCwkU3VjZsq7oiEIdcLE7IaaM0Z8J3okqxdsiFO75VpkkmCUc5YqF5WR8T+Ztt8 6vqzUHvJ+Jmvlth9joD1qOJ/YxO3TLb5RPTDW7JDgyyn+TFBDPfsiVBMwJyVrvlgVagX pAthoBeexejJndWzWyNB4xDdUNQsqhFjjOqWTE2hoGo7zKUHmAbDnJjicHTCYzyegHhU qK/txEWyn9xOUbmewdjG4EuKQWRZf22QazKvE4S87T8jow68VL8YZxR3IbmfyWCOfGc1 v4vgB8/VlvTj8uc5kcCO48jypvlURBizHBQjP2pITSerEIztvFa61UTyn6EVVlCUrg8u AWWA== X-Forwarded-Encrypted: i=1; AJvYcCUVB3AkmZkydqvM7m9yFAFYlSipEyUz4skwl9ULrryhBTD6YGus6owEbbdDvKM2rMkEps3jrmEp/UbEFX0=@vger.kernel.org X-Gm-Message-State: AOJu0YyLf6Ke+dHrJCUDRxC4j8L5Y9SvjBj8sFBS9SgU8h7b1RAGSQDp P/aZxFXXvf1MSzRXYxCn74HVZUz+mfA0gupCTPmwX6UkR9faxfywFWGZzCzeZIAnf93jwhJQh/u ZXJ+DpQ== X-Google-Smtp-Source: AGHT+IGwxqcF5HGKU98QglmRtnsyeeupEdYEOXFBBsc9Evieq/fD8PzoR2iQw1xACcwNtVEbS81mTrskymo= X-Received: from pgvz4.prod.google.com ([2002:a65:6644:0:b0:b6c:f6a5:fdbe]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a21:3383:b0:35f:aa1b:bbff with SMTP id adf61e73a8af0-3614eaf50cbmr41930160637.11.1764641018289; Mon, 01 Dec 2025 18:03:38 -0800 (PST) Reply-To: Sean Christopherson Date: Mon, 1 Dec 2025 18:03:33 -0800 In-Reply-To: <20251202020334.1171351-1-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20251202020334.1171351-1-seanjc@google.com> X-Mailer: git-send-email 2.52.0.107.ga0afd4fd5b-goog Message-ID: <20251202020334.1171351-2-seanjc@google.com> Subject: [PATCH 1/2] KVM: Disallow toggling KVM_MEM_GUEST_MEMFD on an existing memslot From: Sean Christopherson To: Paolo Bonzini Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Alexander Potapenko , Sean Christopherson Content-Type: text/plain; charset="UTF-8" Reject attempts to disable KVM_MEM_GUEST_MEMFD on a memslot that was initially created with a guest_memfd binding, as KVM doesn't support toggling KVM_MEM_GUEST_MEMFD on existing memslots. KVM prevents enabling KVM_MEM_GUEST_MEMFD, but doesn't prevent clearing the flag. Failure to reject the new memslot results in a use-after-free due to KVM not unbinding from the guest_memfd instance. Unbinding on a FLAGS_ONLY change is easy enough, and can/will be done as a hardening measure (in anticipation of KVM supporting dirty logging on guest_memfd at some point), but fixing the use-after-free would only address the immediate symptom. ================================================================== BUG: KASAN: slab-use-after-free in kvm_gmem_release+0x362/0x400 [kvm] Write of size 8 at addr ffff8881111ae908 by task repro/745 CPU: 7 UID: 1000 PID: 745 Comm: repro Not tainted 6.18.0-rc6-115d5de2eef3-next-kasan #3 NONE Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 Call Trace: dump_stack_lvl+0x51/0x60 print_report+0xcb/0x5c0 kasan_report+0xb4/0xe0 kvm_gmem_release+0x362/0x400 [kvm] __fput+0x2fa/0x9d0 task_work_run+0x12c/0x200 do_exit+0x6ae/0x2100 do_group_exit+0xa8/0x230 __x64_sys_exit_group+0x3a/0x50 x64_sys_call+0x737/0x740 do_syscall_64+0x5b/0x900 entry_SYSCALL_64_after_hwframe+0x4b/0x53 RIP: 0033:0x7f581f2eac31 Allocated by task 745 on cpu 6 at 9.746971s: kasan_save_stack+0x20/0x40 kasan_save_track+0x13/0x50 __kasan_kmalloc+0x77/0x90 kvm_set_memory_region.part.0+0x652/0x1110 [kvm] kvm_vm_ioctl+0x14b0/0x3290 [kvm] __x64_sys_ioctl+0x129/0x1a0 do_syscall_64+0x5b/0x900 entry_SYSCALL_64_after_hwframe+0x4b/0x53 Freed by task 745 on cpu 6 at 9.747467s: kasan_save_stack+0x20/0x40 kasan_save_track+0x13/0x50 __kasan_save_free_info+0x37/0x50 __kasan_slab_free+0x3b/0x60 kfree+0xf5/0x440 kvm_set_memslot+0x3c2/0x1160 [kvm] kvm_set_memory_region.part.0+0x86a/0x1110 [kvm] kvm_vm_ioctl+0x14b0/0x3290 [kvm] __x64_sys_ioctl+0x129/0x1a0 do_syscall_64+0x5b/0x900 entry_SYSCALL_64_after_hwframe+0x4b/0x53 Reported-by: Alexander Potapenko Fixes: a7800aa80ea4 ("KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory") Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson --- virt/kvm/kvm_main.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 9eca084bdcbe..8891df136416 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -2085,7 +2085,7 @@ static int kvm_set_memory_region(struct kvm *kvm, return -EINVAL; if ((mem->userspace_addr != old->userspace_addr) || (npages != old->npages) || - ((mem->flags ^ old->flags) & KVM_MEM_READONLY)) + ((mem->flags ^ old->flags) & (KVM_MEM_READONLY | KVM_MEM_GUEST_MEMFD))) return -EINVAL; if (base_gfn != old->base_gfn) -- 2.52.0.107.ga0afd4fd5b-goog