linux-kernel - [PATCH 4.9 58/63] x86, mm: fix gup_pte

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Date:   Mon, 13 Mar 2017 16:39:45 +0800
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Xiong Zhou <xzhou@...hat.com>, Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.9 58/63] x86, mm: fix gup_pte_range() vs DAX mappings

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dan Williams <dan.j.williams@...el.com>

commit ef947b2529f918d9606533eb9c32b187ed6a5ede upstream.

gup_pte_range() fails to check pte_allows_gup() before translating a DAX
pte entry, pte_devmap(), to a page.  This allows writes to read-only
mappings, and bypasses the DAX cacheline dirty tracking due to missed
'mkwrite' faults.  The gup_huge_pmd() path and the gup_huge_pud() path
correctly check pte_allows_gup() before checking for _devmap() entries.

Fixes: 3565fce3a659 ("mm, x86: get_user_pages() for dax mappings")
Link: http://lkml.kernel.org/r/148804251312.36605.12665024794196605053.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
Reported-by: Dave Hansen <dave.hansen@...ux.intel.com>
Reported-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc: Xiong Zhou <xzhou@...hat.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/mm/gup.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/arch/x86/mm/gup.c
+++ b/arch/x86/mm/gup.c
@@ -120,6 +120,11 @@ static noinline int gup_pte_range(pmd_t
 			return 0;
 		}

+		if (!pte_allows_gup(pte_val(pte), write)) {
+			pte_unmap(ptep);
+			return 0;
+		}
+
 		if (pte_devmap(pte)) {
 			pgmap = get_dev_pagemap(pte_pfn(pte), pgmap);
 			if (unlikely(!pgmap)) {
@@ -127,8 +132,7 @@ static noinline int gup_pte_range(pmd_t
 				pte_unmap(ptep);
 				return 0;
 			}
-		} else if (!pte_allows_gup(pte_val(pte), write) ||
-			   pte_special(pte)) {
+		} else if (pte_special(pte)) {
 			pte_unmap(ptep);
 			return 0;
 		}