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 B54E84570C3; Thu, 23 Jul 2026 15:17:20 +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=1784819845; cv=none; b=XV/zFo3e3qdDgMMYam3Mw4vWLoFCIJhkAdTcdBrGc5Ri3obpzZDJi4uSVCTcSUZ6pjHYARzlCq3ODZANf4BlI+5Ao90jv0InGqBvPr0fIBVLpbIen4Ev5gsZq+V4MOM2KUck+zhyZxtdm1JM0pOmxzCL1Eub3BIXNXw+pjPVbMk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784819845; c=relaxed/simple; bh=3isjtK28wb1BiLlMBIpy71VvY1jYYrdz7YUUYuIwCk8=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=S1mjxFrf2boq70rFjiCtNis4vXvYGGaImiIUXmhEoP3J7cwaxqRtJUbDTDaK4W11m+ujGEMUrkqVdUFZw6i1aBiPhohmHJIwvtnQky6tUS2uxb+UfNom68dVxdzMVe6bk6J14PhbaP93imn7jUaI3IBle702k0dalDBAoio5VNA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=OEW0t8w/; 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="OEW0t8w/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 448C61F000E9; Thu, 23 Jul 2026 15:17:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784819838; bh=jGfvVz5phYfszb4vs/wrQwKbo5YfQ9htQgjlD4h0uzo=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=OEW0t8w/ZdlXeERCjc75StArDzDUqbCfBmj/Evab41GuYCBr4ySbLeSLVRFCMGDv+ l/ctMnIh60mbWkTdAktAFmL9qN05WJa8i0aOq5ilbl+d8NsWSz3RRjVbBSouVtRrVM iIkARpos/gy9E6Y6xap1sb5R8kGxxStmgv2YxQD92ZPMdQzDm71GyCKg7SOaoHWpSk msBqA3iq8JznuaUxh2t5IkX+7Si6Kyh0nWI4L6NqqzbExl7eiMUQCzwJtzlqMH+b9D MSEzlmyzhr+pkSk+W/MEA/VPlHCL+klN7I9sn8F3dEM8FlMuu2UxEFYJRfR5FBnSQn jDYMIua2YFiTA== From: "Lorenzo Stoakes (ARM)" Date: Thu, 23 Jul 2026 16:16:32 +0100 Subject: [PATCH mm-hotfixes v6 2/5] x86/mm/pat: acquire init_mm write lock on collapse to avoid UAF Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260723-series-vmap-race-fix-v6-2-8cc77dcc0018@kernel.org> References: <20260723-series-vmap-race-fix-v6-0-8cc77dcc0018@kernel.org> In-Reply-To: <20260723-series-vmap-race-fix-v6-0-8cc77dcc0018@kernel.org> To: Andrew Morton , Suren Baghdasaryan , "Liam R. Howlett" , Vlastimil Babka , Shakeel Butt , David Hildenbrand , Mike Rapoport , Michal Hocko , Uladzislau Rezki , Toshi Kani , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , Kiryl Shutsemau , Catalin Marinas , Will Deacon , Dev Jain , Ryan Roberts Cc: David Carlier , ljs@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-arm-kernel@lists.infradead.org, "Denis V. Lunev" , "Borah, Chaitanya Kumar" , stable@vger.kernel.org X-Mailer: b4 0.15.2 X-Developer-Signature: v=1; a=openpgp-sha256; l=4047; i=ljs@kernel.org; h=from:subject:message-id; bh=3isjtK28wb1BiLlMBIpy71VvY1jYYrdz7YUUYuIwCk8=; b=owGbwMvMwCV2fu7ZrsZH9SKMp9WSGLKSDGJ/vL0Rc3P9G8usFe9mixwynvfEO80n4NQqqbCXw cfUbMpaO0pZGMS4GGTFFFmefxHfHyQSNq/zgr8bzBxWJpAhDFycAjCRG7sY/ufu5Fgs37pTbkL8 3TldD9vP771waZK/w1Pec69qPkXfyX3LyLB0xzdr+6U3D30QfFtaOetH0DOr+mDn5iN5szhtf4p uecAAAA== X-Developer-Key: i=ljs@kernel.org; a=openpgp; fpr=E7F417BF5214569E89D04F46CF9DCD8A81E27F14 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") Cc: stable@vger.kernel.org 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 Signed-off-by: Lorenzo Stoakes (ARM) --- arch/x86/mm/pat/set_memory.c | 15 ++++++++++++++- include/linux/mmap_lock.h | 2 ++ 2 files changed, 16 insertions(+), 1 deletion(-) diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c index d023a40a1e03..d1e63f7d267f 100644 --- a/arch/x86/mm/pat/set_memory.c +++ b/arch/x86/mm/pat/set_memory.c @@ -22,6 +22,7 @@ #include #include #include +#include #include #include @@ -410,7 +411,7 @@ static void __cpa_flush_tlb(void *data) static int collapse_large_pages(unsigned long addr, struct list_head *pgtables); -static void cpa_collapse_large_pages(struct cpa_data *cpa) +static void __cpa_collapse_large_pages(struct cpa_data *cpa) { unsigned long start, addr, end; struct ptdesc *ptdesc, *tmp; @@ -442,6 +443,18 @@ static void cpa_collapse_large_pages(struct cpa_data *cpa) } } +static void cpa_collapse_large_pages(struct cpa_data *cpa) +{ + /* + * Take the mmap write lock on init_mm to: + * - Avoid a use-after-free if raced by ptdump (which takes its own + * write lock on init_mm). + * - Serialise concurrent CPA walkers. + */ + scoped_guard(mmap_write_lock, &init_mm) + __cpa_collapse_large_pages(cpa); +} + static void cpa_flush(struct cpa_data *cpa, int cache) { unsigned int i; diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h index 6b5c2390cc30..047f5f5e2c34 100644 --- a/include/linux/mmap_lock.h +++ b/include/linux/mmap_lock.h @@ -621,6 +621,8 @@ 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(mmap_write_lock, struct mm_struct *, + mmap_write_lock(_T), mmap_write_unlock(_T)) DEFINE_GUARD_COND(mmap_read_lock, _try, mmap_read_trylock(_T)) static inline void mmap_read_unlock_non_owner(struct mm_struct *mm) -- 2.55.0