linux-kernel - [PATCH v2 1/7] mm/mprotect: allow clean exclusive anon pages to be writable

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20221108174652.198904-2-david@redhat.com>
Date:   Tue,  8 Nov 2022 18:46:46 +0100
From:   David Hildenbrand <david@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
        David Hildenbrand <david@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Dave Chinner <david@...morbit.com>,
        Nadav Amit <namit@...are.com>, Peter Xu <peterx@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Hugh Dickins <hughd@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Mike Rapoport <rppt@...nel.org>,
        Anshuman Khandual <anshuman.khandual@....com>
Subject: [PATCH v2 1/7] mm/mprotect: allow clean exclusive anon pages to be writable

From: Nadav Amit <namit@...are.com>

Anonymous pages might have the dirty bit clear, but this should not
prevent mprotect from making them writable if they are exclusive.
Therefore, skip the test whether the page is dirty in this case.

Note that there are already other ways to get a writable PTE mapping an
anonymous page that is clean: for example, via MADV_FREE. In an ideal
world, we'd have a different indication from the FS whether writenotify
is still required.

Signed-off-by: Nadav Amit <namit@...are.com>
[ return directly; update description ]
Signed-off-by: David Hildenbrand <david@...hat.com>
---
 mm/mprotect.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/mm/mprotect.c b/mm/mprotect.c
index 8d770855b591..86a28c0e190f 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -46,7 +46,7 @@ static inline bool can_change_pte_writable(struct vm_area_struct *vma,
 
 	VM_BUG_ON(!(vma->vm_flags & VM_WRITE) || pte_write(pte));
 
-	if (pte_protnone(pte) || !pte_dirty(pte))
+	if (pte_protnone(pte))
 		return false;
 
 	/* Do we need write faults for softdirty tracking? */
@@ -65,11 +65,10 @@ static inline bool can_change_pte_writable(struct vm_area_struct *vma,
 		 * the PT lock.
 		 */
 		page = vm_normal_page(vma, addr, pte);
-		if (!page || !PageAnon(page) || !PageAnonExclusive(page))
-			return false;
+		return page && PageAnon(page) && PageAnonExclusive(page);
 	}
 
-	return true;
+	return pte_dirty(pte);
 }
 
 static unsigned long change_pte_range(struct mmu_gather *tlb,
-- 
2.38.1