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=1794560340; b=iCrD/QigXLywApmK7RBn2YYsxTsvkpy9DoU1mprLGGz30vmefDgm2b5h8E1OgNiHprLr o6Gg63yTrIQ578xlC0xkwg7AVZ60/Nv7815rglXK2BetcXOxsBNZOMbuF0UjTtF+LXuwl SUVMSl9eIzb9PaYc0VmkP7fA6+AMaTFa/5J8GdVzacbSwbbrL0G5cOD68TdAzcL1IBUjM Lh6X8quPrnVvHAQltLJaSJ0/6EP8my9XaPC/i6p6MJoFdVpSA7zOzW33muN+OXa9xZ++p 5/Je0eWcklUMUPsUJ7YHv1cXe4v5WvUttHqvQ1yNoZCKpH4ieh50mDWHJLDLTV73HRg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794560340; h=Received:DKIM-Signature:Message-ID:Date:MIME-Version:User-Agent: Subject:Content-Language:To:Cc:References:From:Autocrypt:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=YF7NHY1fVlGveMHNsJnnjtGJ3+1XgRTTULcBOP2fUbI=; b=AZG+DMFY+Vd5lLKHGrn0vLm/yQsiMbArfrUXNvfSlagp8lMkMlNA1hgwPGEdBDXRQE0t WexZSyYygIdiRVaWIhOn6aknCvarg/b9r/UJWa8GLLAW4CjacqmM6Ak0nLKne8+t2G8sd 0Jy/63zYCRNGUqQaq1+9UryPI/8g6o2LWoHGihr4gi/OK+yf7PV/dCLcSy37hmJthzYWt XIV+J29ixkrW85TCVZhW//ubcoInt1XHh6q9ZxbYXazjpvwxLt1yMijEd0QWfN4Ra4ozl yY0MAem6CCKa2SvElzLr4EJnE402UrTLGuDwEkYHjfmUfZC65s+nsumb7hAk8CUbnxQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=B+Sj1rnL; 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 0597E606A321; Fri, 13 Nov 2026 08:58:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=B+Sj1rnL Received: by smtp.kernel.org (Postfix) with ESMTPSA id EBA721F000C4; Fri, 13 Nov 2026 08:58:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794560339; bh=YF7NHY1fVlGveMHNsJnnjtGJ3+1XgRTTULcBOP2fUbI=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=B+Sj1rnLIABT2rcMAHDb8ZnEfd0jTex4c1qrfj0CSRk0gqZnxgNlbeKj4GqmwtC9I o8Xe/mfzfwZupSsAirIa5j4T99BWCeooiaGkcPxrha+PA2hMxNFQo1B5qgiclciRvJ H/0QS47NbbvNelQKUZaLYxLikkesF1eucTGQ3XHglrVcE3sGxrTRW1h3QpwV9v3R4O YauwalFMafdrHEV4zgip1oDQUDuo7PK7wcQaXMuie0pD5uDbIAM5svIaPto7fRy0mo a6tlA/n7GVSd3t8dEWO4ZLrpdgPAAEY7SBncyX5yBNeewHKMKVczi4UYxnM0JXkXp/ ptXy6a57Iw/5w== Message-ID: <01b19c1e-b87d-4996-acaa-cd5103f30edb@kernel.org> Date: Fri, 13 Nov 2026 09:58:55 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/madvise: disallow guard region installation in uffd-armed VMAs Content-Language: en-US To: "Lorenzo Stoakes (ARM)" , Andrew Morton , "Liam R. Howlett" , David Hildenbrand , Jann Horn , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Shuah Khan Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Tal Zussman , stable@vger.kernel.org References: <20261112-disallow-uffd-guard-install-v1-1-bcf8b1aaa72e@kernel.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSNWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBrZXJuZWwub3JnPsLBsAQTAQoAWhYhBKlA1DSZLC6OmRA9UCJPp+fM gqZkBQJqFFy6GxSAAAAAAAQADm1hbnUyLDIuNSsxLjEyLDIsMgIbAwUJGtCBUAULCQgHAwUV CgkICwUWAgMBAAIeBQIXgAAKCRAiT6fnzIKmZJIUEADFx/tREzUImHrEwVHeSvDFmA7tJysI UVrlvrM09E7GIuzphzv7jYmo8n3ANpCczLEVr4G0syYQdTigaZgv3+FQDIIzhKih1IHhu1Ei XHlywNWKnQxxQEUNi5Mwx43wQz5XVw9F1A7gtKBKNtfogO511hAbrzagrYajyQacEJ/+sfhZ 9Da8ltHIXD8pcYaHUfQgEusCgmEd9+KrUwrTbckFKmYq5chuE6yJ4J0EmWknL096jIE6CnzF FRslQ3B1UKDjxVsm1ZHfir5NeWszLkTvGFsddFaWTgh8UycESG6VQzKXjjewXu2pG7YQYRpj QKm1W5X2TkwWkXRBZTmfmbhxIUMh3+zf5wQ463rSmDN/8v81tdqBtAW6rH/kzg1GvkaTHXn0 507yEHFzBksk2viAuIxxr7km8+/KARYLIdGtx30EG8cKzAUZOK6WqxtNCsXUJNrVE8CWrCaD icoNu7Fs1c5hmPHdSTnU48ce67449DdnO4neLSNhRiGlMHJgfJUmgrxu/hcYeOZ3haWmEQ2w uW1Mh01OHi8QZHCEyAbABrPs9GUgccc/4eYXX9hIgxfSkYzn8f+8NuIFPWl/0uTvjgqU29FQ SbzOLxHq9439Ox40G5mS5eZXRGxITYR+6TXvRGI6P/264jvflnr/pDGUttaikU+0W+1uxgKH cmYbEc7ATQRbGTU1AQgAn0H6UrFiWcovkh6EXVcl+SeqyO6JHOPm+e9Wu0Vw+VIUvXZVUVVQ La1PQDUi6j00ChlcR66g9/V0sPIcSutacPKfdKYOBvzd4rlhL8rfrdEsQw5ApZxrA8kYZVMh FmBRKAa6wos25moTlMKpCWzTH84+WO5+ziCTsTUZASAToz3RdunTD+vQcHj0GqNTPAHK63sf bAB2I0BslZkXkY1RLb/YhuA6E7JyEd2pilZOrIuBGl/5q2qSakgnAVFWFBR/DO27JuAksYnq +aH8vI0xGvwn75KqSk4UzAkDzWSmO4ZHuahKtQgZNsMYV+PGayRBX9b9zbldzopoLBdqHc4n jQARAQABwsF8BBgBCgAmAhsMFiEEqUDUNJksLo6ZED1QIk+n58yCpmQFAmfIHFQFCRYU6J8A CgkQIk+n58yCpmS2PA//bqN1LfcotmArgElsa+0EGZSQlYgK48pm8WAeTXTngudP9IJ4SuKY HR5RNjHcBeqN+Me0zxRqYzRb8nGanHEkDyf4Im8DQM8d6vbyU+FcPmG4skud4kgS1zMHnlVd SXfSIwKC/hKgdHG8aBV7545Lz9X6Iohea+94wneD0aw/hqF+QWewGZhWJriWAZtvEkzNjQOi 4U9F/trLten/x7bpphDSnDMKJtITbtzATT1Dq7o7VpIUK1nCTQALMuMjKCdi8OdU/+V+R3O4 0PXWvX8qrvqYapVbZ+9KqT74FsuB0Ya9uXwgBF2Q6cRuETZk5vqaqKxzqoQZCO8AOz/58j6O 2RHNy/mZEN+7tJ5Tsq42zVJ4jxsT8b9YplavCMsnBgDeRWhcbYhCyttoL7nYISyWg4kQYZ/P wIV3OuNv2f8iKYsxNsRuClOAF82+gvqOy1/1pprFjy8uo2pkoOrb63aOP3vO5VHnRKgra6dq NcaZ+c6J4H+nEJGi2SkHAUJz5oBzuThvPudLvPA/SK8sKoM01IRxSihev/S/5WLazXB1PGem OCbvzC1IjWJJraxiDJ5IygokapUa2RP7+WBR22skQ3SSl6G107QgWKSyTOGWEaRmV53vxQLV jXuCmzSSasTL60zq5yGrT4/DYQVSNEUiUbG4pYekxJujNeEDkUlky0Y= In-Reply-To: <20261112-disallow-uffd-guard-install-v1-1-bcf8b1aaa72e@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/12/26 18:38, Lorenzo Stoakes (ARM) wrote: > In order to establish guard regions, guard markers are installed in the > page tables of a mapped VMA. > > However, problems arise when one tries to combine this with registering a > VMA for userfaultfd, as such operations may themselves need to install page > table markers such as uffd-wp. > > When this installation is attempted the guard marker prevents these markers > being applied, which can lead to unexpected results (especially if the > guard regions are later removed.) > > This is especially problematic because guard region installation causes the > regions to be zapped first, meaning that the removal of userfaultfd-tracked > ranges will not be logged in this case. > > Therefore, disallow this. > > This makes sense as conceptually, guard regions mark a part of a VMA as > effectively unmapped at the page table level, and removing the markers is > like mapping the VMA again, over which operation uffd markers would in any > case be lost. > > Only check for this on installation, as a VMA can be registered for > userfaultfd after guard regions are established. > > In this case, the guard regions cannot have new markers installed, and no > faults can occur in the guard regions, until they are removed, at which > point everything should function normally. So IIUC this means the other order of operations (first guard regions, then uffd) already prevents the two co-existing. Makes sense to prevent the same in the order of uffd and then guard regions then. > A survey of open source users indicates nobody is relying on installing > guard regions in uffd-armed VMAs. Software including glibc, android, > tcmalloc and CRIU were checked. > > Fix the selftest to reflect the change. > > Fixes: 662df3e5c376 ("mm: madvise: implement lightweight guard page mechanism") > Reported-by: Tal Zussman > Closes: https://lore.kernel.org/all/20261111-uffd-state-fixes-v1-9-00713d368976@columbia.edu/ > Closes: https://lore.kernel.org/all/20261111-uffd-state-fixes-v1-10-00713d368976@columbia.edu/ > Closes: https://lore.kernel.org/all/20261111-uffd-state-fixes-v1-11-00713d368976@columbia.edu/ > Cc: stable@vger.kernel.org > Signed-off-by: Lorenzo Stoakes (ARM) Acked-by: Vlastimil Babka (SUSE) > --- > mm/madvise.c | 4 ++++ > tools/testing/selftests/mm/guard-regions.c | 12 ++++++++---- > 2 files changed, 12 insertions(+), 4 deletions(-) > > diff --git a/mm/madvise.c b/mm/madvise.c > index 0214efd2a014..268731e90f12 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -1156,6 +1156,10 @@ static long madvise_guard_install(struct madvise_behavior *madv_behavior) > if (!is_valid_guard_vma(vma, /* allow_locked = */false)) > return -EINVAL; > > + /* Guard markers are incompatible with UFFD markers. */ > + if (userfaultfd_armed(vma)) > + return -EINVAL; > + > /* > * Set atomically under read lock. All pertinent readers will need to > * acquire an mmap/VMA write lock to read it. All remaining readers may > diff --git a/tools/testing/selftests/mm/guard-regions.c b/tools/testing/selftests/mm/guard-regions.c > index 02f69244f9a4..97da54dcf3a4 100644 > --- a/tools/testing/selftests/mm/guard-regions.c > +++ b/tools/testing/selftests/mm/guard-regions.c > @@ -1476,7 +1476,7 @@ TEST_F(guard_regions, cold_pageout) > ASSERT_EQ(munmap(ptr, 10 * page_size), 0); > } > > -/* Ensure that guard pages do not break userfaultd. */ > +/* Ensure that guard regions cannot be installed in uffd-armed VMAs. */ > TEST_F(guard_regions, uffd) > { > const unsigned long page_size = self->page_size; > @@ -1526,10 +1526,15 @@ TEST_F(guard_regions, uffd) > reg.mode = UFFDIO_REGISTER_MODE_MISSING; > ASSERT_EQ(ioctl(uffd, UFFDIO_REGISTER, ®), 0); > > - /* Guard the range. This should not trigger the uffd. */ > + /* Now try to guard, should fail with EINVAL. */ > + ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_INSTALL), -1); > + ASSERT_EQ(errno, EINVAL); > + > + /* Once unregistered, we should be able to guard the range. */ > + ASSERT_EQ(ioctl(uffd, UFFDIO_UNREGISTER, &range), 0); > ASSERT_EQ(madvise(ptr, 10 * page_size, MADV_GUARD_INSTALL), 0); > > - /* The guarding should behave as usual with no uffd intervention. */ > + /* The guarding should behave as usual. */ > for (i = 0; i < 10; i++) { > char *curr = &ptr[i * page_size]; > > @@ -1537,7 +1542,6 @@ TEST_F(guard_regions, uffd) > } > > /* Cleanup. */ > - ASSERT_EQ(ioctl(uffd, UFFDIO_UNREGISTER, &range), 0); > close(uffd); > ASSERT_EQ(munmap(ptr, 10 * page_size), 0); > } > > --- > base-commit: 4318887a3efa4c53d6f083ccfd7105b809a3ac65 > change-id: 20261112-disallow-uffd-guard-install-a5294129ad7b > > Cheers,