From nobody Sun Nov 9 20:22:42 2025 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.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; Authentication-Results: mx.zohomail.com; dkim=fail; spf=pass (zoho.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 1551762797906781.5324323979686; Mon, 4 Mar 2019 21:13:17 -0800 (PST) Received: from localhost ([127.0.0.1]:37577 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1h12O9-00021K-Mv for importer@patchew.org; Tue, 05 Mar 2019 00:13:13 -0500 Received: from eggs.gnu.org ([209.51.188.92]:54533) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1h12Mi-0001Cy-ED for qemu-devel@nongnu.org; Tue, 05 Mar 2019 00:11:45 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1h12Mh-0005qj-Jc for qemu-devel@nongnu.org; Tue, 05 Mar 2019 00:11:44 -0500 Received: from ozlabs.org ([2401:3900:2:1::2]:56483) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1h12Mg-0005mz-Rs; Tue, 05 Mar 2019 00:11:43 -0500 Received: by ozlabs.org (Postfix, from userid 1007) id 44D4kL1l9vz9s47; Tue, 5 Mar 2019 16:11:38 +1100 (AEDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gibson.dropbear.id.au; s=201602; t=1551762698; bh=cswdvFfIgyqvGN/o6bK8yh8/+qNC6VyOyrGbbfmYugc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=PdLm19NSqfjaKR9NVd0TMusrJhj5lbQtmE9mIHY8RhM1P1sKdImK2YzcWPW5Qc2py xR85au0CYbRxOuN4oDo6ZxG9NltvA+IIwYIGPM7wa3WmWvqbXMZv8pVJiOz8WLTIt5 X7bLK4Z2sJtev7+eDOzp9N78CsM04MDsCB6pyxPQ= From: David Gibson To: mst@redhat.com, david@redhat.com Date: Tue, 5 Mar 2019 16:11:33 +1100 Message-Id: <20190305051134.27930-2-david@gibson.dropbear.id.au> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190305051134.27930-1-david@gibson.dropbear.id.au> References: <20190305051134.27930-1-david@gibson.dropbear.id.au> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 2401:3900:2:1::2 Subject: [Qemu-devel] [RFC 1/2] virtio-balloon: Fix possible guest memory corruption with inflates & deflates X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-ppc@nongnu.org, qemu-devel@nongnu.org, David Gibson Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) Content-Type: text/plain; charset="utf-8" This fixes a balloon bug with a nasty consequence - potentially corrupting guest memory - but which is extremely unlikely to be triggered in practice. The balloon always works in 4kiB units, but the host could have a larger page size on certain platforms. Since ed48c59 "virtio-balloon: Safely handle BALLOON_PAGE_SIZE < host page size" we've handled this by accumulating requests to balloon 4kiB subpages until they formed a full host page. Since f6deb6d "virtio-balloon: Remove unnecessary MADV_WILLNEED on deflate" we essentially ignore deflate requests. Suppose we have a host with 8kiB pages, and one host page has subpages A & B. If we get this sequence of events - inflate A deflate A inflate B - the current logic will discard the whole host page. That's incorrect because the guest has deflated subpage A, and could have written important data to it. This patch fixes the problem by adjusting our state information about partially ballooned host pages when deflate requests are received. Fixes: ed48c59 "virtio-balloon: Safely handle BALLOON_PAGE_SIZE < host page= size" Signed-off-by: David Gibson --- hw/virtio/virtio-balloon.c | 48 ++++++++++++++++++++++++++++++++++++-- 1 file changed, 46 insertions(+), 2 deletions(-) diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c index d3f2913a85..e5e82b556d 100644 --- a/hw/virtio/virtio-balloon.c +++ b/hw/virtio/virtio-balloon.c @@ -111,6 +111,43 @@ static void balloon_inflate_page(VirtIOBalloon *balloo= n, } } =20 +static void balloon_deflate_page(VirtIOBalloon *balloon, + MemoryRegion *mr, hwaddr offset) +{ + void *addr =3D memory_region_get_ram_ptr(mr) + offset; + RAMBlock *rb; + size_t rb_page_size; + ram_addr_t ram_offset, host_page_base; + + /* XXX is there a better way to get to the RAMBlock than via a + * host address? */ + rb =3D qemu_ram_block_from_host(addr, false, &ram_offset); + rb_page_size =3D qemu_ram_pagesize(rb); + host_page_base =3D ram_offset & ~(rb_page_size - 1); + + if (balloon->pbp + && rb =3D=3D balloon->pbp->rb + && host_page_base =3D=3D balloon->pbp->base) { + int subpages =3D rb_page_size / BALLOON_PAGE_SIZE; + + /* + * This means the guest has asked to discard some of the 4kiB + * subpages of a host page, but then changed its mind and + * asked to keep them after all. It's exceedingly unlikely + * for a guest to do this in practice, but handle it anyway, + * since getting it wrong could mean discarding memory the + * guest is still using. */ + bitmap_clear(balloon->pbp->bitmap, + (ram_offset - balloon->pbp->base) / BALLOON_PAGE_SIZE, + subpages); + + if (bitmap_empty(balloon->pbp->bitmap, subpages)) { + free(balloon->pbp); + balloon->pbp =3D NULL; + } + } +} + static const char *balloon_stat_names[] =3D { [VIRTIO_BALLOON_S_SWAP_IN] =3D "stat-swap-in", [VIRTIO_BALLOON_S_SWAP_OUT] =3D "stat-swap-out", @@ -314,8 +351,15 @@ static void virtio_balloon_handle_output(VirtIODevice = *vdev, VirtQueue *vq) =20 trace_virtio_balloon_handle_output(memory_region_name(section.= mr), pa); - if (!qemu_balloon_is_inhibited() && vq !=3D s->dvq) { - balloon_inflate_page(s, section.mr, section.offset_within_= region); + if (!qemu_balloon_is_inhibited()) { + if (vq =3D=3D s->ivq) { + balloon_inflate_page(s, section.mr, + section.offset_within_region); + } else if (vq =3D=3D s->dvq) { + balloon_deflate_page(s, section.mr, section.offset_wit= hin_region); + } else { + g_assert_not_reached(); + } } memory_region_unref(section.mr); } --=20 2.20.1