From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9CCB04CCDE8; Tue, 1 Sep 2026 06:03:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788242607; cv=none; b=taK3fZkioM3dHKy2qKvyu5zYEuxS2Asrvv4JI1dxksvtexdQEV9qznH7nymwdtLle1I3UWJDSxt9miUi0OmTXI9eAzyFv/hXAK0zfhiZ18f+qE9lPX6bkxgwKrFhKknGVEVRiymVmyOBOEpo3DAiur1Na2RNp+NOYCebx1pVbI0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788242607; c=relaxed/simple; bh=EMILxeSo+x247RV8NHHT526oEoCUszKjH0K8y9tHbPs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=hknNz1k4PNv3HDxwQf/YzGOfRAC9/CmY3h+SMELMWlIAp5I0yHH+W0PPCQYLVgJNS2+YlEnipkjRJc1C87eTagtqQquy2TEzbQHxj09loEVbhslmeFVAJbZgalWgytHzgac2WaBOcyqufXZhpeWg1A6syuM20pgYOcEPuiKLJVQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=MUhhVyOw; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="MUhhVyOw" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5ED331F000E9; Tue, 1 Sep 2026 06:03:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788242606; bh=OVVXt6GL/R8LJuqc2RyttdvOJVfaBZ9xBw2X4e233ZI=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=MUhhVyOwcEp4HPu4Hpq3eXRNrfCeVbDYxsEItQhTwKCEOCTJBgGPimPAYXiVMXRm5 KxXPYs6FlAjLeibRwDqpu8hEhq4geSlr5sRws3WKXI0CmrbdW22WNlK/fX7BB1OmKC wkXldLmkyUF0EHGZ8Girh5GhTy7ufzRDnkMATzULhDfgFSfc9+/kyzbSrl3FaZKIfz GnA2102sdMy5dlNQY5jgjHDRMUVmSjMQWdUlLzcKdF9SuINcoi03MmBZj5Wpwc79GR Vxk/lKf8hYn8UtMgTPIsWlcmVVqgs+Skn4Ohb/iTnVdouYfETRn5oso1LneCaopZ3j mJp3IJeMfG4LA== Message-ID: Date: Tue, 1 Sep 2026 08:03:21 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [tip: x86/urgent] x86/mm/pat: Acquire init_mm write lock on collapse to avoid UAF To: linux-kernel@vger.kernel.org, linux-tip-commits@vger.kernel.org Cc: "Lorenzo Stoakes (ARM)" , "Mike Rapoport (Microsoft)" , Dave Hansen , "Kiryl Shutsemau (Meta)" , "David Hildenbrand (Arm)" , Will Deacon , David Carlier , Atish Patra , Nikunj A Dadhania , stable@vger.kernel.org, x86@kernel.org References: <20260813-cpa-fixes-v2-1-39b4ff90f91d@kernel.org> <178821524784.3717435.3293914321834699913.tip-bot2@tip-bot2> Content-Language: en-US From: Jiri Slaby Autocrypt: addr=jirislaby@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 01. 09. 26, 0:27, tip-bot2 for Lorenzo Stoakes (ARM) wrote: > The following commit has been merged into the x86/urgent branch of tip: > > Commit-ID: be4f4ab413d15e2b44f6bcda3b607eb707a7712e > Gitweb: https://git.kernel.org/tip/be4f4ab413d15e2b44f6bcda3b607eb707a7712e > Author: Lorenzo Stoakes (ARM) > AuthorDate: Thu, 13 Aug 2026 12:01:24 +03:00 > Committer: Dave Hansen > CommitterDate: Mon, 31 Aug 2026 15:14:58 -07:00 The committed patch to tip is bogus. It contains only the guard definition. > x86/mm/pat: Acquire init_mm write lock on collapse to avoid UAF > > x86 implements page attribute modification using its Change Page > Attributes (CPA) mechanism. > > This tracks properties of ranges such as cache mode through x86 page > attributes, and as part of that logic manipulates kernel page tables. > > Since commit 41d88484c71c ("x86/mm/pat: restore large ROX pages after > fragmentation") ranges of kernel page table entries can be collapsed into > huge page table entries as part of this logic. > > As part of this collapse, it frees the page tables which the collapsed > entries previously pointed to, and it does so without any relevant locks > being held to preclude concurrent kernel page table walkers. > > The only way this code can be reached is if CPA_COLLAPSE is specified, and > this is only set in set_memory_rox() via: > > set_memory_rox() > -> change_page_attr_set_clr() > -> cpa_flush() > -> cpa_collapse_large_pages() > > Notable users of this are execmem and bpf when manipulating executable > mappings. > > However, this is problematic for ptdump as it walks ranges it does not own > and thus runs the risk of a use-after-free on page tables freed underneath > it. > > In addition, concurrent CPA collapse operations are possible which can also > cause races. > > Resolve the issue by acquiring the mmap write lock on init_mm across the > whole operation. > > It is safe to acquire a sleeping lock as all the callers invoke > set_memory_rox() from process context and in any case, > change_page_attr_set_clr() calls vm_unmap_alias() which ultimately takes a > mutex, disallowing atomic context here. > > Fixes: 41d88484c71c ("x86/mm/pat: restore large ROX pages after fragmentation") > Signed-off-by: Lorenzo Stoakes (ARM) > Signed-off-by: Mike Rapoport (Microsoft) > Signed-off-by: Dave Hansen > Reviewed-by: Mike Rapoport (Microsoft) > Reviewed-by: Kiryl Shutsemau (Meta) > Reviewed-by: David Hildenbrand (Arm) > Reviewed-by: Dave Hansen > Reviewed-by: Will Deacon > Reviewed-by: David Carlier > Tested-by: Atish Patra > Tested-by: Nikunj A Dadhania > Cc:stable@vger.kernel.org > Link: https://patch.msgid.link/20260813-cpa-fixes-v2-1-39b4ff90f91d@kernel.org > --- > include/linux/mmap_lock.h | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h > index bec0eab..b8a13b8 100644 > --- a/include/linux/mmap_lock.h > +++ b/include/linux/mmap_lock.h > @@ -630,6 +630,8 @@ static inline void mmap_read_unlock(struct mm_struct *mm) > DEFINE_GUARD(mmap_read_lock, struct mm_struct *, > mmap_read_lock(_T), mmap_read_unlock(_T)) > DEFINE_GUARD_COND(mmap_read_lock, _try, mmap_read_trylock(_T)) > +DEFINE_GUARD(mmap_write_lock, struct mm_struct *, > + mmap_write_lock(_T), mmap_write_unlock(_T)) > > static inline void mmap_read_unlock_non_owner(struct mm_struct *mm) > { > -- js suse labs