From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793829141; b=xsTC4zcpOqdQ9N7ol48+DTjg2sUREZkmscQghXgD7sGrHiDU5P8mG66j4zQuWkF5PD27 AVtd21SWKmVxVWY4sN+ncle0Z9eNp5jmO8vDUFlIlKRJaEcl43Sm0JDhnNSncMqLxvGHp RFT9R1nVbyAc/xll2ngXQBJEBOHRd3+BzFvYVfIn7giF6GhJo+JqrlIlOF/yIBOUQPHiM 91Ai5lGjRrVslyJI98Pq8TX3ceegq5ae9xU/0KqRyfbHyI7jQY/HQQ4Y/c8CTQ57+KzUv FMke5EmhGhDUHTmKhu6tIAo9qZWqQLJL8I7R8XrEQTgz01GTjETAsuCo3I8Cn07a3Rg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793829141; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=xVZPv0fuIr1Xm5BnitwJ/YYi1yh+np/oefdc8rIM06k=; b=giqB67zWngYqQU+qqnI+TKBF7ckTR6G30uPFApYp+dIfZLcyOWqJpf3lFw0MdFFRgOq7 Y+hwu/HJQmhEfTbUXhGGHeuHcdfbPJ4XmU7KwU19YkUEWD1kMDzEi7Q3iWLmoXAjyEvnp n09ScsRY0lwplQGgGku/Y9VHEHqLoGyjgCw0/Xse/G5QVJ/ZKczxssMldKyqnN4sFWMQy xAU6XIHzYxvYoXkzVvsF/glM/jT8yAwUkoRhN/c+GCbAQ5AEDLH78URimEUTJ1ohbVx35 D0p8M/sFDsu/R3yvStELI0aeufX7IrueFXxHgdv5g7KPZr06LnzcbtQP0WNlPI6FFyA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=DaYxH9NS; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 72334608F113; Wed, 4 Nov 2026 21:52:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=DaYxH9NS Received: by smtp.kernel.org (Postfix) with ESMTPSA id 13BB41F00919; Wed, 4 Nov 2026 21:52:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1793829141; bh=xVZPv0fuIr1Xm5BnitwJ/YYi1yh+np/oefdc8rIM06k=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=DaYxH9NSxjKd/lW+RC4dvxOzEGc5TTdKAMgy5ApKzE0SWbdEEqMXcyAlz4xLJf6H3 6yLHJLs8aL8RH3FceF4HlC6Hn9F+rbC0gh+wtk5UmdWBZB2YF/nL6ffkHSkP7pzsh5 TW1m7eLbQaeH3Q+e9YTlMn9yn86EhVRx+fAxAJkU= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Stefan Teodorescu , Vitaly Kuznetsov , Sean Christopherson Subject: [PATCH 7.3 471/547] KVM: x86: Zero reserved synic flags when delivering message to avoid stack leak Date: Wed, 4 Nov 2026 16:10:55 -0500 Message-ID: <20261104211051.746908542@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261104211038.406938024@linuxfoundation.org> References: <20261104211038.406938024@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: patches@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 7.3-stable review patch. If anyone has any objections, please let me know. ------------------ From: Sean Christopherson commit 2616f497506a772db53e7bb1024cde50b4c165e0 upstream. Ensure all reserved flags are zeroed when setting the msg_pending flag as part of SynIC message delivery, as setting only msg_pending can leak seven bits of kernel stack data to the guest. E.g. gcc typically uses a bitwise-OR to set the msg_pending flag, without initializing the on-stack variable. Precisely zero the flags, e.g. as opposed to zeroing the entire structure, to make it somewhat more obvious that the flags *need* to be zeroed. E.g. it would be quite easy to misread the initial read of guest memory and think that zeroing the entire structure is completely superfluous. Fixes: 3a0e7731724f ("x86: kvm: hyperv: simplify SynIC message delivery") Cc: stable@vger.kernel.org Reported-by: Stefan Teodorescu Reviewed-by: Vitaly Kuznetsov Link: https://patch.msgid.link/20260826184449.814130-1-seanjc@google.com Signed-off-by: Sean Christopherson Signed-off-by: Greg Kroah-Hartman --- arch/x86/kvm/hyperv.c | 2 ++ 1 file changed, 2 insertions(+) --- a/arch/x86/kvm/hyperv.c +++ b/arch/x86/kvm/hyperv.c @@ -802,7 +802,9 @@ static int synic_deliver_msg(struct kvm_ if (no_retry) return 0; + hv_hdr.message_flags.asu8 = 0; hv_hdr.message_flags.msg_pending = 1; + r = kvm_vcpu_write_guest_page(vcpu, msg_page_gfn, &hv_hdr.message_flags, msg_off +