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c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=wJmj1iwdc/6FYUJoRp9ESNvSHdufeLrHWgUs3tjf2EE=; b=qF3UigToO1fk1RnPPNWNcGvic4voLD1yQsSwRFt8OtCUdTPs0B8Zb11n+VhpMJWB81 N6Dxz+fYEszWFmWwR7+EHNtRAP5lSETdmc71kVblJa2Dx/lFsCPT53egEX+LF5Jhx55i b6lvO9HVosE9YRUzEx3cG3NQPenf5YEo37k6G8r/ifsCwSAZXGYfkFOc4/ezQU9rd1gd k5dHVUOcuYuPhX49sfn13VX3NAuZK54MH1TfpLjnf/60S++/hTT+Brd0ahzvhrfKPE5E vdyLZfNWI+Ftbx+Wnf17YIARE3FQHFxeIGhCaFN+ai20QHOlp8SJoqS5wQW8hC69yrIt qGoA== X-Gm-Message-State: ANoB5pndPwV/6STET1Jj2rwWqLN7I39DdAIowckkpEPXg8nUtCqB/0F1 Ry49YnsDbexkQbwcxbS0dd3bIbVuaLgaQvmkkaYftg== X-Google-Smtp-Source: AA0mqf4KU6A3b6Li3zUpy2Lk4NYsLCO5Vb2lIVcs9rriQ0Q+7mChaGrUEW7i5q9Wla6p3bnPzAWT9xBCYnFvII50m5Y= X-Received: by 2002:ab0:238f:0:b0:411:968:212 with SMTP id b15-20020ab0238f000000b0041109680212mr3471849uan.107.1668756594737; Thu, 17 Nov 2022 23:29:54 -0800 (PST) MIME-Version: 1.0 References: <20221106021657.1145519-1-pedro.falcato@gmail.com> <202211061948.46D3F78@keescook> <202211171402.95121B3FD4@keescook> In-Reply-To: <202211171402.95121B3FD4@keescook> From: David Gow Date: Fri, 18 Nov 2022 15:29:43 +0800 Message-ID: Subject: Re: Attaching userspace VM to kernel thread (was Re: [PATCH] fs/binfmt_elf: Fix memsz > filesz handling) To: Kees Cook Cc: Matthew Wilcox , linux-mm@kvack.org, Pedro Falcato , linux-kernel@vger.kernel.org, sam@gentoo.org, Alexander Viro , Eric Biederman , linux-fsdevel@vger.kernel.org, Rich Felker , linux-kselftest@vger.kernel.org, kunit-dev@googlegroups.com Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-256; boundary="00000000000011339f05edb9ac95" ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1668756595; a=rsa-sha256; cv=none; b=WM9S652mO+OGY51GXf53OGgHTrIM8gEbNWNKxXDZgBObHbLPmeslTV4ol2NCRbncNQS9wd OFgmKQBgh1CHbsl3rWToipkbjfcP2qo5ZCJVrVe6odd+DDOptYcjXlpsoj6alroDX4FJNh Qcof0wdwa4QxUnh+Z2zYEStptzY8hKI= ARC-Authentication-Results: i=1; imf04.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=Gfgxf5nh; spf=pass (imf04.hostedemail.com: domain of davidgow@google.com designates 209.85.222.42 as permitted sender) smtp.mailfrom=davidgow@google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1668756595; 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-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=wJmj1iwdc/6FYUJoRp9ESNvSHdufeLrHWgUs3tjf2EE=; b=DiOHwGzN6f2/r8+jwy7oq07LMvR8cWFZi0XAK5lIe8Nz6yQ4aRu3cUdP1vCjPK2EGo5ZZ5 7m6XTOTUOheSAHSDFkEyLlg84NT00zg/qq4dEwl7VAxC9FeGGqShdmqMVLo9sJGz//7ivS YvOcvbwkMykB5HhE4oVcHMUNQOhZvIA= X-Stat-Signature: 4j3ti1q8wjto7s61kjy3itsjx5bc6j3u X-Rspamd-Queue-Id: AC85B40008 Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=Gfgxf5nh; spf=pass (imf04.hostedemail.com: domain of davidgow@google.com designates 209.85.222.42 as permitted sender) smtp.mailfrom=davidgow@google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1668756595-7595 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: --00000000000011339f05edb9ac95 Content-Type: text/plain; charset="UTF-8" On Fri, Nov 18, 2022 at 6:06 AM Kees Cook wrote: > > Hi, > > This has diverged from the original topic a bit, so I've changed the > Subject to hopefully gain visibility. :) > > For KUnit, it would be REALLY nice to have a way to attach a userspace > VM to a kernel thread so we can do userspace memory mapping > manipulation, etc. Neither David nor I have been able to figure out the > right set of steps to make this happen. What are we missing? > > Details below... > > On Wed, Nov 16, 2022 at 12:34:40PM +0800, David Gow wrote: > > On Mon, Nov 7, 2022 at 11:59 AM Kees Cook wrote: > > > > > > On Sun, Nov 06, 2022 at 02:16:57AM +0000, Pedro Falcato wrote: > > > David, has there been any work on adding a way to instantiate > > > userspace VMAs in a KUnit test? I tried to write this myself, but I > > > couldn't figure out how to make the userspace memory mappings appear. > > > Here's my fumbling attempt: > > > https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/log/?h=devel/kunit/usercopy > > > > > > I really wish KUnit had userspace mapping support -- I have a bunch of > > > unit tests that need to get built up around checking for regressions > > > here, etc. > > > > Hi Kees, > > > > Sorry the the delayed response! > > > > Alas, my attempts to get this to work haven't been much more > > successful than yours. It's definitely something we'd like to support, > > but I confess to not knowing enough about the mm code to know exactly > > what would be involved. > > > > The workaround is to load tests as modules, and use something like > > Vitor's original patch here: > > https://lore.kernel.org/all/20200721174036.71072-1-vitor@massaru.org/ > > > > Basically, using the existing mm of the module loader. Adapting those > > changes to your branch (and fixing a couple of back-to-front KUnit > > assertions) does work for me when built as a module, in an x86_64 vm: > > > > root@slicestar:~# modprobe usercopy_kunit > > [ 52.986290] # Subtest: usercopy > > [ 52.986701] 1..1 > > [ 53.246058] ok 1 - usercopy_test > > [ 53.246628] ok 1 - usercopy > > > > But getting it to work with built-in tests hasn't been successful so > > far. I wondered if we could just piggy-back on init_mm or similar, but > > that doesn't seem to work either. > > > > So, in the short-term, this is only possible for modules. If that's > > useful enough, we can get Vitor's support patch (or something similar) > > in, and just mark any tests module-only (or have them skip if there's > > no mm). Because kunit.py only runs built-in tests, though, it's > > definitely less convenient. > > Thanks for any pointers! :) > > -Kees > > -- > Kees Cook FWIW, I had another quick look at this yesterday, and I suspect that (at least one of) the problem(s) is that function pointers like mm->get_unmapped_area are only setup as part of exec(), so a newly-created mm isn't actually useful. Looking at, e.g., arch_pick_mm_layout(), there's a whole bunch of architecture-dependent stuff here to handle, e.g., 32-bit compat. 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