From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 11998C432C0 for ; Sun, 1 Dec 2019 01:51:35 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id C7B872084D for ; Sun, 1 Dec 2019 01:51:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="THT/rLMx" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C7B872084D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 759A56B02B0; Sat, 30 Nov 2019 20:51:34 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 7095E6B02B2; Sat, 30 Nov 2019 20:51:34 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6240A6B02B3; Sat, 30 Nov 2019 20:51:34 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0226.hostedemail.com [216.40.44.226]) by kanga.kvack.org (Postfix) with ESMTP id 4C7AD6B02B0 for ; Sat, 30 Nov 2019 20:51:34 -0500 (EST) Received: from smtpin24.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with SMTP id 05A8F181AEF0B for ; Sun, 1 Dec 2019 01:51:34 +0000 (UTC) X-FDA: 76214895708.24.mouth29_da4590faae21 X-HE-Tag: mouth29_da4590faae21 X-Filterd-Recvd-Size: 4840 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf44.hostedemail.com (Postfix) with ESMTP for ; Sun, 1 Dec 2019 01:51:33 +0000 (UTC) Received: from localhost.localdomain (c-73-231-172-41.hsd1.ca.comcast.net [73.231.172.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id B0102215A5; Sun, 1 Dec 2019 01:51:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1575165093; bh=5YG5SJgJYRkpy/Jj3Zis4wmBxE1XZBfNejKoHe/VckI=; h=Date:From:To:Subject:From; b=THT/rLMxIS3YchSgfxZz5Oh8h0BG/75EblcSjLXA2wQcK/Us5+xX8aJngbmv6uxAp YKZx7+OCYsQnOacpLv7wud6vZjmFBNfaaBjUAp9gIr0uacqeIwuwadh61cyOXtjfvq VBIS+WypFFnQ8FHZVtOODQXuCHgWMZKSfClKfChw= Date: Sat, 30 Nov 2019 17:51:32 -0800 From: akpm@linux-foundation.org To: akpm@linux-foundation.org, arnd@arndb.de, kirill.shutemov@linux.intel.com, linux-mm@kvack.org, mm-commits@vger.kernel.org, stable@vger.kernel.org, thellstrom@vmware.com, torvalds@linux-foundation.org, willy@infradead.org Subject: [patch 045/158] mm/memory.c: fix a huge pud insertion race during faulting Message-ID: <20191201015132.LxbEPLRfg%akpm@linux-foundation.org> User-Agent: s-nail v14.8.16 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: Thomas Hellstrom Subject: mm/memory.c: fix a huge pud insertion race during faulting A huge pud page can theoretically be faulted in racing with pmd_alloc() in __handle_mm_fault(). That will lead to pmd_alloc() returning an invalid pmd pointer. Fix this by adding a pud_trans_unstable() function similar to pmd_trans_unstable() and check whether the pud is really stable before using the pmd pointer. Race: Thread 1: Thread 2: Comment create_huge_pud() Fallback - not taken. create_huge_pud() Taken. pmd_alloc() Returns an invalid pointer. This will result in user-visible huge page data corruption. Note that this was caught during a code audit rather than a real experienced problem. It looks to me like the only implementation that currently creates huge pud pagetable entries is dev_dax_huge_fault() which doesn't appear to care much about private (COW) mappings or write-tracking which is, I believe, a prerequisite for create_huge_pud() falling back on thread 1, but not in thread 2. Link: http://lkml.kernel.org/r/20191115115808.21181-2-thomas_os@shipmail.org Fixes: a00cc7d9dd93 ("mm, x86: add support for PUD-sized transparent hugepages") Signed-off-by: Thomas Hellstrom Acked-by: Kirill A. Shutemov Cc: Arnd Bergmann Cc: Matthew Wilcox Cc: Signed-off-by: Andrew Morton --- include/asm-generic/pgtable.h | 25 +++++++++++++++++++++++++ mm/memory.c | 6 ++++++ 2 files changed, 31 insertions(+) --- a/include/asm-generic/pgtable.h~mm-fix-a-huge-pud-insertion-race-during-faulting +++ a/include/asm-generic/pgtable.h @@ -938,6 +938,31 @@ static inline int pud_trans_huge(pud_t p } #endif +/* See pmd_none_or_trans_huge_or_clear_bad for discussion. */ +static inline int pud_none_or_trans_huge_or_dev_or_clear_bad(pud_t *pud) +{ + pud_t pudval = READ_ONCE(*pud); + + if (pud_none(pudval) || pud_trans_huge(pudval) || pud_devmap(pudval)) + return 1; + if (unlikely(pud_bad(pudval))) { + pud_clear_bad(pud); + return 1; + } + return 0; +} + +/* See pmd_trans_unstable for discussion. */ +static inline int pud_trans_unstable(pud_t *pud) +{ +#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && \ + defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD) + return pud_none_or_trans_huge_or_dev_or_clear_bad(pud); +#else + return 0; +#endif +} + #ifndef pmd_read_atomic static inline pmd_t pmd_read_atomic(pmd_t *pmdp) { --- a/mm/memory.c~mm-fix-a-huge-pud-insertion-race-during-faulting +++ a/mm/memory.c @@ -4010,6 +4010,7 @@ static vm_fault_t __handle_mm_fault(stru vmf.pud = pud_alloc(mm, p4d, address); if (!vmf.pud) return VM_FAULT_OOM; +retry_pud: if (pud_none(*vmf.pud) && __transparent_hugepage_enabled(vma)) { ret = create_huge_pud(&vmf); if (!(ret & VM_FAULT_FALLBACK)) @@ -4036,6 +4037,11 @@ static vm_fault_t __handle_mm_fault(stru vmf.pmd = pmd_alloc(mm, vmf.pud, address); if (!vmf.pmd) return VM_FAULT_OOM; + + /* Huge pud page fault raced with pmd_alloc? */ + if (pud_trans_unstable(vmf.pud)) + goto retry_pud; + if (pmd_none(*vmf.pmd) && __transparent_hugepage_enabled(vma)) { ret = create_huge_pmd(&vmf); if (!(ret & VM_FAULT_FALLBACK)) _