From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 61BD1225A23; Mon, 23 Jun 2025 22:26:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750717597; cv=none; b=dEcGtUe7bpmUtZCmtPyRQLKdWrG8IArRJmvkEfpkWfE6v21apvnFym9vdjgv8/m7JzfqjIV6JwsCF39t5obtCfo+oP1UMVviFIKAnfx642pz3dTp0eQ+HX4nb6fv/TgiVbgesViiDfIAVly1fm4pvepq01mgGKImbvGJXlSQDps= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750717597; c=relaxed/simple; bh=X0M7VkEWuKZhv2yMZzXllbI3iarWkJ66V+MjJwBE1DM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=XZA9lTbYT2sQHkdjsGQ5prrQcY7Q01ldZ48EPb2QQDxT7+/8QngK6LZ2TqHuOyK66CJIO7n4OO6M5GOUlHTgmsb7oLeVceu4YKSKb6vKS4T/3qRPQBqNvqTXzumGSWm5AsSJCcSJSRcvUQ0LOsGQuSBUmVaIrDLHESoa6O+vNLs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=CF0g1uj3; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="CF0g1uj3" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EBDD0C4CEF3; Mon, 23 Jun 2025 22:26:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1750717597; bh=X0M7VkEWuKZhv2yMZzXllbI3iarWkJ66V+MjJwBE1DM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=CF0g1uj322o+acWq6dzwe3ajqslUXrrw9FzzbJ2KhMVebtubz5xp80IxmS/JOU+d7 4yt7fingkB4MBHQ4ew/XqjwJkrbvr86S9CCmQVT5fddsFP9coSb3CQt+xBVXIDszQS EbkpaYeMJIHhnAm2yuIwnkvkIMFX9Rh4YMw4RXLM= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Jann Horn , Lorenzo Stoakes , Liam Howlett , Muchun Song , Oscar Salvador , Vlastimil Babka , Andrew Morton Subject: [PATCH 6.1 465/508] mm/hugetlb: fix huge_pmd_unshare() vs GUP-fast race Date: Mon, 23 Jun 2025 15:08:30 +0200 Message-ID: <20250623130656.551708083@linuxfoundation.org> X-Mailer: git-send-email 2.50.0 In-Reply-To: <20250623130645.255320792@linuxfoundation.org> References: <20250623130645.255320792@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jann Horn commit 1013af4f585fccc4d3e5c5824d174de2257f7d6d upstream. huge_pmd_unshare() drops a reference on a page table that may have previously been shared across processes, potentially turning it into a normal page table used in another process in which unrelated VMAs can afterwards be installed. If this happens in the middle of a concurrent gup_fast(), gup_fast() could end up walking the page tables of another process. While I don't see any way in which that immediately leads to kernel memory corruption, it is really weird and unexpected. Fix it with an explicit broadcast IPI through tlb_remove_table_sync_one(), just like we do in khugepaged when removing page tables for a THP collapse. Link: https://lkml.kernel.org/r/20250528-hugetlb-fixes-splitrace-v2-2-1329349bad1a@google.com Link: https://lkml.kernel.org/r/20250527-hugetlb-fixes-splitrace-v1-2-f4136f5ec58a@google.com Fixes: 39dde65c9940 ("[PATCH] shared page table for hugetlb page") Signed-off-by: Jann Horn Reviewed-by: Lorenzo Stoakes Cc: Liam Howlett Cc: Muchun Song Cc: Oscar Salvador Cc: Vlastimil Babka Cc: Signed-off-by: Andrew Morton Signed-off-by: Jann Horn Signed-off-by: Greg Kroah-Hartman --- mm/hugetlb.c | 7 +++++++ 1 file changed, 7 insertions(+) --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -7162,6 +7162,13 @@ int huge_pmd_unshare(struct mm_struct *m return 0; pud_clear(pud); + /* + * Once our caller drops the rmap lock, some other process might be + * using this page table as a normal, non-hugetlb page table. + * Wait for pending gup_fast() in other threads to finish before letting + * that happen. + */ + tlb_remove_table_sync_one(); atomic_dec(&virt_to_page(ptep)->pt_share_count); mm_dec_nr_pmds(mm); return 1;