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=1794357606; b=uvD3LwCsiVBwtz5kZMUjUEiO5a42coWSeE+d0NtY+OBseHs0NdmQM2ZKEhT3YxcAmUiu ikJWwCbK3VDAsnP05WD9tzu7Xwxwd5sdOteATulMaP0DxSifSEyys9MbqWVM7jWqYjVJl 98107wnr/VDz354zq+6wyznPhEGqES8dqHvlB03xQBkmFVpeBtS5UgyZAnaCj4KwvgVT2 BCCKixZmdCu9dN1gYTdvmwRtFWf0WbZrCgVu92VY4q2GrmxXy0AaU0qv02Ez/dDNMO+Z1 wXAmhrA02XjfSwpFoR53dVDkwzWeZosiy7ZrR6QwOXwSseBye62i5lnsRgcbn114hCQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794357606; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=jkmSTbGwMIOC0T+8o1yU4rbcfj4SPDTHyaqUcehnT+A=; b=YA/j9Wq6/NX4dkZctg493eBDPYKZtqGYN8o+/2q1KF877Hq13Fef/X4btG8jDMC/dZ9X XyDJ9ynNS1Yj1S7hIeDesAFL5d7UO8W/MAvzarkT81NKo/x6ROIdQp40kRt4FHWZUhOvi tuIrT+uRt/EsFRTQ0uMxMEfRXTdcJzGc/4P/Oh9/s6woGxSIoRg/9uBjRNtPl2kgaH71s skr/mOuKJ8k+g7Hsmtlh97ShYZmHxQkjHV1kwK7LYIZmqDsGaq2CZdK39vizpfmXtEHIz EtMEbQxtQJSymrMZpYg9HsSFAfr92exSfQNXIGSZsZvJGvfl1r2qbOhrG4rDe103xuQ== 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=NGvfxhVJ; 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 8E085606A327 for ; Wed, 11 Nov 2026 00:40:06 +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=NGvfxhVJ Received: by smtp.kernel.org (Postfix) with ESMTPSA id 233041F0093D; Wed, 11 Nov 2026 00:40:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794357606; bh=jkmSTbGwMIOC0T+8o1yU4rbcfj4SPDTHyaqUcehnT+A=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=NGvfxhVJOwoYRrSK51KZ2w0h80lOYnEqxjN6CBLvru4r+GsIUrk2LrzpHziiElqR+ 43FyD9CBAxjR+Q/xTwB8RGzAF5WSQUr6L5cj8GwGd23hYUUf0SW2a3zRFzRi+ZN6oc QVsw9lRrr+6gTH+MnPo7XXtP9r6i3p7vxF8slz5dj+FWfcA08GOxOFAkNe4+IXnD2/ K2+W//THgK8N2532X1p9k99GFBtJm/N16pw+4Z6VJ9A3sDiZijvj5OuKrBDWKI2G3d Pwok1GgYFrI0Rhjx2+6t7y81HexnezMlnGWS+tt86moKW7Dbt7PuPWu/i02QjM5hHx FciiU4GCTxLIg== From: Sasha Levin To: stable@vger.kernel.org Cc: Nickolai Zeldovich , Andrew Morton , Pedro Falcato , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , Sasha Levin Subject: [PATCH 5.10.y] mm/mlock: use a long for the page count in mlock_fixup() Date: Tue, 10 Nov 2026 19:40:03 -0500 Message-ID: <20261111003710.290413-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261107062840-failed-5.10-3ae91e3079b1@kernel.org> References: <20261107062840-failed-5.10-3ae91e3079b1@kernel.org> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Nickolai Zeldovich [ Upstream commit 3ae91e3079b1504ef162b2884454d5f1421f4eb9 ] mlock_fixup() adjusts mm->locked_vm, an unsigned long, by the number of pages whose VM_LOCKED state it changes, but computes that number in an int: int nr_pages; ... nr_pages = (end - start) >> PAGE_SHIFT; ... mm->locked_vm += nr_pages; When a single VMA range of 2^31 pages (8 TiB with 4 KiB pages) or more is locked or unlocked, the count is truncated to 32 bits and then sign-extended, so locked_vm is changed by the wrong amount, while munmap(), mremap() and the other paths that maintain locked_vm use the full unsigned long page count. Such a range is reachable on 64-bit architectures with a 47-bit or larger user address space (x86_64, arm64 with 48-bit VA, riscv64 Sv48) by a task with CAP_IPC_LOCK or a raised RLIMIT_MEMLOCK, which do_mlock() checks against the full untruncated length. It costs nothing with MAP_NORESERVE and MLOCK_ONFAULT/MCL_ONFAULT, since then no page is populated. On x86_64, after p = mmap(NULL, 8UL << 40, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS | MAP_NORESERVE, -1, 0); mlock2(p, 8UL << 40, MLOCK_ONFAULT); VmLck in /proc/self/status reads 18446744065119617024 kB instead of 8589934592 kB; munmap() of the region then subtracts the true size and leaves VmLck at 18446744056529682432 kB instead of 0. With 16 TiB, locked_vm is not changed at all, VmLck stays 0 kB, and after the task drops CAP_IPC_LOCK or lowers RLIMIT_MEMLOCK, mlock(), mmap(MAP_LOCKED) and the other mlock_future_ok() and account_locked_vm() users enforce RLIMIT_MEMLOCK against that count, so they let the task lock memory beyond its limit (or, in the 8 TiB case, refuse every further lock). The error persists for the life of the mm; unlocking the range in pieces skews it further. The wrong count is per-mm accounting only: it does not change which pages are locked. The int has been there since before git history (the variable was named "pages" until it was renamed in 2.6.28); every other updater of locked_vm uses an unsigned long or long count. Make nr_pages a long, which holds the page count of any user range and its negation, so the existing sign handling is unchanged. Found by formal verification of mm/mlock.c against the kernel binary. Link: https://lore.kernel.org/20261014131358.780240-1-nickolai@csail.mit.edu Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Nickolai Zeldovich Signed-off-by: Andrew Morton Reviewed-by: Pedro Falcato Assisted-by: LLM Cc: Liam R. Howlett Cc: Lorenzo Stoakes Cc: Vlastimil Babka Cc: Jann Horn Cc: [ sashal: adjusted context to match the existing mlock_fixup() signature and local variable declarations ] Signed-off-by: Sasha Levin --- mm/mlock.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/mlock.c b/mm/mlock.c index 884b1216da6a6..91b736be6d95f 100644 --- a/mm/mlock.c +++ b/mm/mlock.c @@ -526,7 +526,7 @@ static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev, { struct mm_struct *mm = vma->vm_mm; pgoff_t pgoff; - int nr_pages; + long nr_pages; int ret = 0; int lock = !!(newflags & VM_LOCKED); vm_flags_t old_flags = vma->vm_flags; -- 2.53.0