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 69B5C4315A; Mon, 23 Jun 2025 21:41:15 +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=1750714875; cv=none; b=d9FAB/R8tDEN/xC9/oqfD9twW19PaDDlfY5+0ugcKxt0HUcDA8gTPjJfDz16/kwB/znfpZbIYGWiCce3OqfaLbaC6N0b6z/Ood7ERaJ4T8kVptsRVs7bT9JN8nKyL8w6vtKiJ2uB6oi7AOhDOdRTZV+LvRb5SRc1/72RYQao6J4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750714875; c=relaxed/simple; bh=stGUxqe74GuuiVWq6gUgttU7opMJKdQqjaEMs+gDoT8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=XAOhadgcWQ+2aThr4qcRK9bRX3B1UDm8akHEfh7u9zrqVI9/k3njB4xER0/XhRaS6tew532cwUehC7JjFQGqc7oyg+P6Kixr2uESC9/K6btycFyE3lhWTdnB4kYm2OqlkTOo8wpD7BZO6pRL8Tsq1iq9ecaU+VK/6209JrUDS3s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=e4TIE4/L; 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="e4TIE4/L" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 053CBC4CEEA; Mon, 23 Jun 2025 21:41:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1750714875; bh=stGUxqe74GuuiVWq6gUgttU7opMJKdQqjaEMs+gDoT8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=e4TIE4/Ll7bWLHkeUAS6x3SglUOxHXOEfxF4nIASalaLhCdQ6vAaF+0Bjf+sPaIfD gG3RJbEzjcs6DoBc64jhacvoLQm7YdPEzxSQzH2Gl9m5VjTFQQCq5wW+zvgQt01PVg 4zGwyHkYpviYX1Lxhz3OYrDSdtgssjl6lp6Rw3zU= 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 6.12 162/414] mm/hugetlb: fix huge_pmd_unshare() vs GUP-fast race Date: Mon, 23 Jun 2025 15:04:59 +0200 Message-ID: <20250623130646.086903834@linuxfoundation.org> X-Mailer: git-send-email 2.50.0 In-Reply-To: <20250623130642.015559452@linuxfoundation.org> References: <20250623130642.015559452@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 6.12-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: Greg Kroah-Hartman --- mm/hugetlb.c | 7 +++++++ 1 file changed, 7 insertions(+) --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -7252,6 +7252,13 @@ 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(); ptdesc_pmd_pts_dec(virt_to_ptdesc(ptep)); mm_dec_nr_pmds(mm); return 1;