From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D23DAC433EF for ; Tue, 30 Nov 2021 15:40:41 +0000 (UTC) Received: from localhost ([::1]:57470 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ms5FI-0008Le-ID for qemu-devel@archiver.kernel.org; Tue, 30 Nov 2021 10:40:40 -0500 Received: from eggs.gnu.org ([209.51.188.92]:33970) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ms5D9-0007XS-Ja for qemu-devel@nongnu.org; Tue, 30 Nov 2021 10:38:27 -0500 Received: from [2a00:1450:4864:20::532] (port=44581 helo=mail-ed1-x532.google.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1ms5D7-00040K-AF for qemu-devel@nongnu.org; Tue, 30 Nov 2021 10:38:27 -0500 Received: by mail-ed1-x532.google.com with SMTP id l25so88279729eda.11 for ; Tue, 30 Nov 2021 07:38:24 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nuviainc-com.20210112.gappssmtp.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:content-transfer-encoding:in-reply-to; bh=Qf584jFjWNb07yDBC2ZkXE9VxW+y18ZBj1K8J2mx0SI=; b=hBTWGDqFElYA+fJL9KbcBdnwRXEMiLCq9l6vvTVSC8moIeaiFZFKT+cq8SfmG3ryqC 26JaCyzHSJaiHBAToxdJDnbpxaaukuc+4g9daecc/bj9XP6WHZqxzcklAVVH0RO3znWh zjOk/saHU4ZflRgr66jfdIdLi8W82YIJSgmcMoR5S+A5lIglCgUDmOf4ta3la/JIbMDi Oy7waflkLP3hJdSDzEpbLwXstwUO0ykYeRH7DwC9Wc+z1NI/B1P81Co5tewd5EulEkJZ ya7SJ5sw3z2/bz4kfQO/uscPO4QF5N0TffaV7knIdCBiqdpviAguHgjE2M/AUvReGzrO Xuhw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:content-transfer-encoding :in-reply-to; bh=Qf584jFjWNb07yDBC2ZkXE9VxW+y18ZBj1K8J2mx0SI=; b=ayy0GyKnxg25Qt7TDLHyCJx76Lcw+zVtWvuOgvk1OT5HHxTt0rWVcJ1RdDwri6mMdk cok2J9KEvBKjZ0ZzCAnF/dYotBfQvMwNvswHx0lLIBOdZtwq0wEayt4kfoZ7PmfFXAU1 a952D8uKSefD7dG/OC2NzYHEYwBVlVKz8ld6D5Af5qTVUIpULDbopmJXZNWQ9IZQUCw/ 6mPA0HEcYw6Mzihm6szzh6EcPuKMcaUrdUMAVF30ZrSSAnhKR8jQb7QPlhqhqEOg10Br 9CdAwoxSSE0o4hgfSyw2HqED7JxXv4O9inONa73Gk+blCwJtNfONaW8g8CEs8JRgY5ZC rCKg== X-Gm-Message-State: AOAM533dJkW44uN9nBd1CrHmpSpB2pWI4BnYMPJn6EDSgJEn6PYU6q4p L+HjXNYXNEoPjQ3zyL3vzCFzGw== X-Google-Smtp-Source: ABdhPJwcOwxnC+/M6QSo/iW+sKropBlJunmYeJviqEZ3FmmkDe4vSV8br73cyei9xru0XWKCaf3luQ== X-Received: by 2002:a05:6402:42d5:: with SMTP id i21mr83263432edc.373.1638286702888; Tue, 30 Nov 2021 07:38:22 -0800 (PST) Received: from localhost ([82.44.17.50]) by smtp.gmail.com with ESMTPSA id go10sm9475317ejc.115.2021.11.30.07.38.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 30 Nov 2021 07:38:22 -0800 (PST) Date: Tue, 30 Nov 2021 15:38:21 +0000 From: Jamie Iles To: Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= Subject: Re: [PATCH 2/2] hw/core/loader: workaround read() size limit. Message-ID: References: <20211111141141.3295094-1-jamie@nuviainc.com> <20211111141141.3295094-3-jamie@nuviainc.com> <7e490883-b723-1ff6-9191-6ef0c91ccd25@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Host-Lookup-Failed: Reverse DNS lookup failed for 2a00:1450:4864:20::532 (failed) Received-SPF: pass client-ip=2a00:1450:4864:20::532; envelope-from=jamie@nuviainc.com; helo=mail-ed1-x532.google.com X-Spam_score_int: -10 X-Spam_score: -1.1 X-Spam_bar: - X-Spam_report: (-1.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, PDS_HP_HELO_NORDNS=0.001, RCVD_IN_DNSWL_NONE=-0.0001, RDNS_NONE=0.793, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=no 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: , Cc: qemu-devel@nongnu.org, lmichel@kalray.eu Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Hi Philippe, On Thu, Nov 11, 2021 at 05:04:56PM +0000, Jamie Iles wrote: > On Thu, Nov 11, 2021 at 04:55:35PM +0100, Philippe Mathieu-Daudé wrote: > > On 11/11/21 16:43, Philippe Mathieu-Daudé wrote: > > > On 11/11/21 16:36, Jamie Iles wrote: > > >> Hi Philippe, > > >> > > >> On Thu, Nov 11, 2021 at 03:55:48PM +0100, Philippe Mathieu-Daudé wrote: > > >>> Hi Jamie, > > >>> > > >>> On 11/11/21 15:11, Jamie Iles wrote: > > >>>> On Linux, read() will only ever read a maximum of 0x7ffff000 bytes > > >>>> regardless of what is asked. If the file is larger than 0x7ffff000 > > >>>> bytes the read will need to be broken up into multiple chunks. > > >>>> > > >>>> Cc: Luc Michel > > >>>> Signed-off-by: Jamie Iles > > >>>> --- > > >>>> hw/core/loader.c | 40 ++++++++++++++++++++++++++++++++++------ > > >>>> 1 file changed, 34 insertions(+), 6 deletions(-) > > >>>> > > >>>> diff --git a/hw/core/loader.c b/hw/core/loader.c > > >>>> index 348bbf535bd9..16ca9b99cf0f 100644 > > >>>> --- a/hw/core/loader.c > > >>>> +++ b/hw/core/loader.c > > >>>> @@ -80,6 +80,34 @@ int64_t get_image_size(const char *filename) > > >>>> return size; > > >>>> } > > >>>> > > >>>> +static ssize_t read_large(int fd, void *dst, size_t len) > > >>>> +{ > > >>>> + /* > > >>>> + * man 2 read says: > > >>>> + * > > >>>> + * On Linux, read() (and similar system calls) will transfer at most > > >>>> + * 0x7ffff000 (2,147,479,552) bytes, returning the number of bytes > > >>> > > >>> Could you mention MAX_RW_COUNT from linux/fs.h? > > >>> > > >>>> + * actually transferred. (This is true on both 32-bit and 64-bit > > >>>> + * systems.) > > >>> > > >>> Maybe "This is true for both ILP32 and LP64 data models used by Linux"? > > >>> (because that would not be the case for the ILP64 model). > > >>> > > >>> Otherwise s/systems/Linux variants/? > > >>> > > >>>> + * > > >>>> + * So read in chunks no larger than 0x7ffff000 bytes. > > >>>> + */ > > >>>> + size_t max_chunk_size = 0x7ffff000; > > >>> > > >>> We can declare it static const. > > >> > > >> Ack, can fix all of those up. > > >> > > >>>> + size_t offset = 0; > > >>>> + > > >>>> + while (offset < len) { > > >>>> + size_t chunk_len = MIN(max_chunk_size, len - offset); > > >>>> + ssize_t br = read(fd, dst + offset, chunk_len); > > >>>> + > > >>>> + if (br < 0) { > > >>>> + return br; > > >>>> + } > > >>>> + offset += br; > > >>>> + } > > >>>> + > > >>>> + return (ssize_t)len; > > >>>> +} > > >>> > > >>> I see other read()/pread() calls: > > >>> > > >>> hw/9pfs/9p-local.c:472: tsize = read(fd, (void *)buf, bufsz); > > >>> hw/vfio/common.c:269: if (pread(vbasedev->fd, &buf, size, > > >>> region->fd_offset + addr) != size) { > > >>> ... > > >>> > > >>> Maybe the read_large() belongs to "sysemu/os-xxx.h"? > > >> > > >> I think util/osdep.c would be a good fit for this. To make sure we're > > > > > > Yes. > > > > > >> on the same page though are you proposing converting all pread/read > > >> calls to a qemu variant or auditing for ones that could potentially take > > >> a larger size? > > > > > > Yes, I took some time wondering beside loading blob in guest memory, > > > what would be the other issues you might encounter. I couldn't find > > > many cases. Eventually hw/vfio/. I haven't audit much, only noticed > > > hw/9pfs/9p-local.c and qga/commands-*.c (not sure if relevant), but > > > since we want to fix this, I'd rather try to fix it globally. > > > > Actually what you suggest is simpler, add qemu_read() / qemu_pread() > > in util/osdep.c, convert all uses without caring about any audit. > > Okay, this hasn't worked out too badly - I'll do the same for > write/pwrite too and then switch all of the callers over with a > coccinelle patch so it'll be a fairly large diff but simple. > > We could elect to keep any calls with a compile-time constant length > with the unwrapped variants but I think that's probably more confusing > in the long-run. Coming back to this I think this is probably a non-starter because of non-blocking file descriptors. There is already a qemu_write_full so I'm inclined to add qemu_read_full following the same pattern and then convert all of the read calls in the loader to use that. Thanks, Jamie