From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 5411F34EEEE; Tue, 6 Jan 2026 17:27:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767720460; cv=none; b=Oh3+caHh3pZaK9Re1jVhJ9nGBfIIDdrsOYUtXBdDaHPBgCURiJRH2etgjxbeIBZAHJNUrwg4B3BKSrqiu2zCrsdbP4yw1dzsHM/kWCDLNH5Z2s2N0OZm+Ja3Civbbl8bQQFYtFa8tq32xjSLKiejyfoK9Z9p7eZUl4ncniasPvs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767720460; c=relaxed/simple; bh=kAc/DvJ8ADYHlVvgnTi9GZlJcMTvmqjD21imr2avACg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=BiLddZjxhpquoriIVIdsH8JsirkArtU/OktTyApdI3EEnW8v+KxkSKNRFPB2sdFog4XrdrmlvAcl4Z3ttjjbruam4dhcBT2L0myDRGnV6L3tCVCXT2IDnjnSD+U+qkulNB8UjKuuc9B/XEgEYWrrC+22AJLnxSvob1mfZyVOwPQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=AdyyRSHj; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="AdyyRSHj" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CFFBCC16AAE; Tue, 6 Jan 2026 17:27:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1767720460; bh=kAc/DvJ8ADYHlVvgnTi9GZlJcMTvmqjD21imr2avACg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=AdyyRSHjlnKfB/LV5gc9+dpdpcyG/miVW7ZIVYZlWbXRMKHGP+TMEUpZf7w+o3A76 tAZzBdcEQAiNKYlpEy0Jf+RPoS5PkDRQqwtUWGBook4LtqLYFIt3kT3ibeGJBfXAyz EchLK5BSrLivKEKiOPgKX0tWF/qsIbVZ4vCkub4Y= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Alexander Potapenko , Sean Christopherson Subject: [PATCH 6.12 211/567] KVM: Disallow toggling KVM_MEM_GUEST_MEMFD on an existing memslot Date: Tue, 6 Jan 2026 17:59:53 +0100 Message-ID: <20260106170459.127664389@linuxfoundation.org> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260106170451.332875001@linuxfoundation.org> References: <20260106170451.332875001@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Sean Christopherson commit 9935df5333aa503a18de5071f53762b65c783c4c upstream. 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 Link: https://patch.msgid.link/20251202020334.1171351-2-seanjc@google.com Signed-off-by: Sean Christopherson Signed-off-by: Greg Kroah-Hartman --- virt/kvm/kvm_main.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -2062,7 +2062,7 @@ int __kvm_set_memory_region(struct 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)