linux-kernel - [BUG] mm: thp: hugepage_vma

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-next>] [day] [month] [year] [list]

Message-Id: <1390345671-136133-1-git-send-email-athorlton@sgi.com>
Date:	Tue, 21 Jan 2014 17:07:49 -0600
From:	Alex Thorlton <athorlton@....com>
To:	linux-kernel@...r.kernel.org
Cc:	Alex Thorlton <athorlton@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>, linux-mm@...ck.org
Subject: [BUG] mm: thp: hugepage_vma_check has a blind spot

hugepage_vma_check is called during khugepaged_scan_mm_slot to ensure
that khugepaged doesn't try to allocate THPs in vmas where they are
disallowed, either due to THPs being disabled system-wide, or through
MADV_NOHUGEPAGE.

The logic that hugepage_vma_check uses doesn't seem to cover all cases,
in my opinion.  Looking at the original code:

       if ((!(vma->vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
	   (vma->vm_flags & VM_NOHUGEPAGE))

We can see that it's possible to have THP disabled system-wide, but still
receive THPs in this vma.  It seems that it's assumed that just because
khugepaged_always == false, TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG must be
set, which is not the case.  We could have VM_HUGEPAGE set, but have THP
set to "never" system-wide, in which case, the condition presented in the
if will evaluate to false, and (provided the other checks pass) we can
end up giving out a THP even though the behavior is set to "never."

While we do properly check these flags in khugepaged_has_work, it looks
like it's possible to sleep after we check khugepaged_hask_work, but
before hugepage_vma_check, during which time, hugepages could have been
disabled system-wide, in which case, we could hand out THPs when we
shouldn't be.

This small fix makes hugepage_vma_check work more like
transparent_hugepage_enabled, checking if THPs are set to "always"
system-wide, then checking if THPs are set to "madvise," as well as
making sure that VM_HUGEPAGE is set for this vma.

Signed-off-by: Alex Thorlton <athorlton@....com>
Reported-by: Alex Thorlton <athorlton@....com>
Cc: Andrew Morton <akpm@...ux-foundation.org> 
Cc: Mel Gorman <mgorman@...e.de> 
Cc: Rik van Riel <riel@...hat.com> 
Cc: Ingo Molnar <mingo@...nel.org> 
Cc: Peter Zijlstra <peterz@...radead.org> 
Cc: linux-mm@...ck.org 
Cc: linux-kernel@...r.kernel.org 

---
 mm/huge_memory.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 95d1acb..f62fba9 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2394,7 +2394,8 @@ static struct page

 static bool hugepage_vma_check(struct vm_area_struct *vma)
 {
-	if ((!(vma->vm_flags & VM_HUGEPAGE) && !khugepaged_always()) ||
+	if ((!khugepaged_always() ||
+	     (!(vma->vm_flags & VM_HUGEPAGE) && !khugepaged_req_madv())) ||
 	    (vma->vm_flags & VM_NOHUGEPAGE))
 		return false;

-- 
1.7.12.4

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/