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 28EC3390608; Fri, 7 Aug 2026 15:38:40 +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=1786117121; cv=none; b=ADAHEHx4ZVxz7iDZ+Rvi4NSV2Y22G3xJimr4fCOS+ujx9TGJrZfCcTRekRPBPj9uhIMvMldw1Vs4T3m/1QyMxwSiB61fl3mNgmNHexQ11vRtOeaFh7WIAZjKf1ejzeUeRjQwaRj/RiwrGd5hoPfP8iZU9ymSkL1gYy+GYEopFjg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786117121; c=relaxed/simple; bh=eFuHM2vDD2RzRuJnIvek+VZKsxO0mZAyY7eP9Ga2+BA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=tgZFkVXLJdxwgrzsySqmnzl/7QryRrd+LM2kz0yy71jQiPd4ieLzXs5rpGAuRHktV4o9xXmDna7D4MsCBnuBrDuoLYnODOu0hXosQNVqsfYVgPi5rrE+5NJyHJFb893ZIhWkiDVt9qEhGH0u2+OtYN3pTYkxNBhGt0Fy93OwvSo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=hR2k3Xtv; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="hR2k3Xtv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 88C6A1F000E9; Fri, 7 Aug 2026 15:38:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1786117120; bh=W37jdG94oX6eCkIs205L3MSq+8BWVLCSzT89mM1woQs=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=hR2k3Xtv86saDkFkrHPD4D8oIncv2QWE6mttCIELR8KcRDarP3v3pa/d69xer0uWK OJSCMCmkTvxfDHUjP3nJw+RA00riQQbnuBqd2oHoeE7C6LVMsxqxbJVPXWb41wN16c Yipp89Ugl7dkCMsBX9kpIQbj0dfYlvBSPpIUC5Ls= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Kiryl Shutsemau , Sashiko AI review , David Hildenbrand , Muchun Song , Oscar Salvador , Peter Xu , Andrew Morton Subject: [PATCH 7.1 205/438] mm/hugetlb: fix swap entry corruption when clearing uffd-wp at fork() Date: Fri, 7 Aug 2026 16:36:41 +0200 Message-ID: <20260807143432.389952630@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260807143428.008222056@linuxfoundation.org> References: <20260807143428.008222056@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 7.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Kiryl Shutsemau (Meta) commit 83abe2fd5b3aeb3123b5408a5a91709c5538fb23 upstream. copy_hugetlb_page_range() clears the uffd-wp bit of migration and hwpoison entries with huge_pte_clear_uffd_wp(), which operates on the present-PTE bit position. Swap entries keep the uffd-wp state elsewhere -- the migration branch reads and sets it with pte_swp_uffd_wp() and pte_swp_mkuffd_wp() -- and the present-PTE position falls into the swap payload. On x86-64 it lands in the inverted swap offset, where a naturally-aligned hugetlb PFN always has the affected bit set, so the clear advances the encoded PFN by two pages. No userfaultfd needs to be involved: the clear is guarded only by the child VMA not being uffd-wp registered, so a plain fork() with an in-flight hugetlb migration entry (or a poisoned hugetlb page) corrupts the entry copied into the child. Instrumenting the clear and forking after MADV_HWPOISON on a 2MB anon hugetlb page shows: offset before=120e00 offset after =120e02 The fallout is mostly latent: rmap walks match migration entries by folio range and remove_migration_pte() rebuilds the PTE from the folio, so a within-folio PFN skew heals once migration completes. But any path that re-encodes the corrupted offset -- e.g. hugetlb_change_protection() rewriting a writable migration entry via make_readable_migration_entry(swp_offset(entry)) -- propagates it. Migration entries legitimately carry uffd-wp, so clear it with pte_swp_clear_uffd_wp(), matching copy_nonpresent_pte() and move_huge_pte(). A hwpoison entry, on the other hand, never carries the uffd-wp bit: it is installed fresh by make_hwpoison_entry() (try_to_unmap_one() does not preserve uffd-wp on the hwpoison path) and hugetlb_change_protection() leaves hwpoison entries untouched. There was nothing to clear there, only the corruption, so drop the clear entirely. Link: https://lore.kernel.org/20260708090110.136162-1-kirill@shutemov.name Fixes: bc70fbf269fd ("mm/hugetlb: handle uffd-wp during fork()") Signed-off-by: Kiryl Shutsemau Reported-by: Sashiko AI review Closes: https://lore.kernel.org/all/20260703140011.99E601F000E9@smtp.kernel.org/ Suggested-by: David Hildenbrand Acked-by: David Hildenbrand (Arm) Assisted-by: Claude:claude-fable-5 Cc: Muchun Song Cc: Oscar Salvador Cc: Peter Xu Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- mm/hugetlb.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4917,8 +4917,12 @@ again: softleaf = softleaf_from_pte(entry); if (unlikely(softleaf_is_hwpoison(softleaf))) { - if (!userfaultfd_wp(dst_vma)) - entry = huge_pte_clear_uffd_wp(entry); + /* + * A hwpoison entry never carries the uffd-wp bit: it is + * installed fresh by make_hwpoison_entry() and + * hugetlb_change_protection() leaves it untouched, so + * there is nothing to clear for the child. + */ set_huge_pte_at(dst, addr, dst_pte, entry, sz); } else if (unlikely(softleaf_is_migration(softleaf))) { bool uffd_wp = pte_swp_uffd_wp(entry); @@ -4936,7 +4940,7 @@ again: set_huge_pte_at(src, addr, src_pte, entry, sz); } if (!userfaultfd_wp(dst_vma)) - entry = huge_pte_clear_uffd_wp(entry); + entry = pte_swp_clear_uffd_wp(entry); set_huge_pte_at(dst, addr, dst_pte, entry, sz); } else if (unlikely(pte_is_marker(entry))) { const pte_marker marker = copy_pte_marker(softleaf, dst_vma);