From nobody Thu Nov 20 14:14:11 2025 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; dkim=fail; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1763399453518273.4620996682082; Mon, 17 Nov 2025 09:10:53 -0800 (PST) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1vL2kZ-0003FW-GN; Mon, 17 Nov 2025 12:10:47 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1vL2kT-00033b-Mu for qemu-devel@nongnu.org; Mon, 17 Nov 2025 12:10:42 -0500 Received: from mlugg.co.uk ([2001:19f0:7401:8244:5400:ff:fe24:ff33] helo=mail.mlugg.co.uk) by eggs.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1vL2kR-0006GB-Vm for qemu-devel@nongnu.org; Mon, 17 Nov 2025 12:10:41 -0500 Received: from localhost.localdomain (3.c.0.2.2.e.e.a.9.8.5.7.2.1.b.b.f.b.9.2.0.c.b.a.0.b.8.0.1.0.0.2.ip6.arpa [IPv6:2001:8b0:abc0:29bf:bb12:7589:aee2:20c3]) by mail.mlugg.co.uk (Postfix) with ESMTPSA id 67E4435A1F; Mon, 17 Nov 2025 17:10:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mlugg.co.uk; s=20200703; t=1763399431; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=3sbIpdXlqwqmTBhiIu3GcMxjkWPw2uw95lJmCAqaivE=; b=H0eG4I4/fGKTdvwUZq58prOUn3tToruMVVqkstrmrJwaBrINHwHVHtA5HH7Ev8xK30wzGY uct1rebgQ8foQhVVPZBHGWd4xC6/YbKxOUeuI2nwl32L34hLdXAkjIvNQxsNvCYD62n1jJ bjcJ30/SZRJcjiicGe/2W74DwmWfNeU= From: Matthew Lugg To: qemu-devel@nongnu.org Cc: laurent@vivier.eu, peter.maydell@linaro.org, Matthew Lugg Subject: [PATCH v2 3/4] linux-user: fix reserved_va page leak in do_munmap Date: Mon, 17 Nov 2025 17:09:53 +0000 Message-ID: <20251117170954.31451-4-mlugg@mlugg.co.uk> X-Mailer: git-send-email 2.51.2 In-Reply-To: <20251117170954.31451-1-mlugg@mlugg.co.uk> References: <20251117170954.31451-1-mlugg@mlugg.co.uk> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=2001:19f0:7401:8244:5400:ff:fe24:ff33; envelope-from=mlugg@mlugg.co.uk; helo=mail.mlugg.co.uk X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: fail (Header signature does not verify) X-ZM-MESSAGEID: 1763399456574158500 Content-Type: text/plain; charset="utf-8" The old logic had an off-by-one bug. For instance, assuming 4k pages on host and guest, if 'len' is '4097' (indicating to unmap 2 pages), then 'last =3D start + 4096', so 'real_last =3D start + 4095', so ultimately 'real_len =3D 4096'. I do not believe this could cause any observable bugs in guests, because `target_munmap` page-aligns the length it passes in. However, calls to this function in `target_mremap` do not page-align the length, so those calls could "drop" pages, leading to a part of the reserved region becoming unmapped. At worst, a host allocation could get mapped into that hole, then clobbered by a new guest mapping. Signed-off-by: Matthew Lugg Reviewed-by: Richard Henderson --- linux-user/mmap.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) The refactor in the last revision has been dropped in favour of a simple two-line patch. The added 'ROUND_UP' on the first line of the diff is neces= sary to prevent the last 'for (prot =3D 0, ...' in the function from considering= a page which 'len' partially covers. diff --git a/linux-user/mmap.c b/linux-user/mmap.c index 6163f1a0d1..4bcfaf7894 100644 --- a/linux-user/mmap.c +++ b/linux-user/mmap.c @@ -1029,9 +1029,9 @@ static int mmap_reserve_or_unmap(abi_ulong start, abi= _ulong len) void *host_start; int prot; =20 - last =3D start + len - 1; + last =3D ROUND_UP(start + len, TARGET_PAGE_SIZE) - 1; real_start =3D start & -host_page_size; - real_last =3D ROUND_UP(last, host_page_size) - 1; + real_last =3D ROUND_UP(last + 1, host_page_size) - 1; =20 /* * If guest pages remain on the first or last host pages, --=20 2.51.2