linux-kernel - [PATCH] mm/mmu_notifier: mm/rmap.c: Fix a mmu_notifier range bug in try_to_unmap

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Message-Id: <20190110005117.18282-1-sean.j.christopherson@intel.com>
Date:   Wed,  9 Jan 2019 16:51:17 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, leozinho29_eu@...mail.com,
        Mike Galbraith <efault@....de>,
        Adam Borowski <kilobyte@...band.pl>,
        Jérôme Glisse <jglisse@...hat.com>,
        Christian König <christian.koenig@....com>,
        Jan Kara <jack@...e.cz>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Ross Zwisler <zwisler@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Felix Kuehling <felix.kuehling@....com>,
        Ralph Campbell <rcampbell@...dia.com>,
        John Hubbard <jhubbard@...dia.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH] mm/mmu_notifier: mm/rmap.c: Fix a mmu_notifier range bug in try_to_unmap_one

The conversion to use a structure for mmu_notifier_invalidate_range_*()
unintentionally changed the usage in try_to_unmap_one() to init the
'struct mmu_notifier_range' with vma->vm_start instead of @address,
i.e. it invalidates the wrong address range.  Revert to the correct
address range.

Manifests as KVM use-after-free WARNINGs and subsequent "BUG: Bad page
state in process X" errors when reclaiming from a KVM guest due to KVM
removing the wrong pages from its own mappings.

Reported-by: leozinho29_eu@...mail.com
Reported-by: Mike Galbraith <efault@....de>
Reported-by: Adam Borowski <kilobyte@...band.pl>
Cc: Jérôme Glisse <jglisse@...hat.com>
Cc: Christian König <christian.koenig@....com>
Cc: Jan Kara <jack@...e.cz>
Cc: Matthew Wilcox <mawilcox@...rosoft.com>
Cc: Ross Zwisler <zwisler@...nel.org>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Radim Krčmář <rkrcmar@...hat.com>
Cc: Michal Hocko <mhocko@...nel.org>
Cc: Felix Kuehling <felix.kuehling@....com>
Cc: Ralph Campbell <rcampbell@...dia.com>
Cc: John Hubbard <jhubbard@...dia.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Fixes: ac46d4f3c432 ("mm/mmu_notifier: use structure for invalidate_range_start/end calls v2")
Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---

FWIW, I looked through all other calls to mmu_notifier_range_init() in
the patch and didn't spot any other unintentional functional changes.

 mm/rmap.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index 68a1a5b869a5..0454ecc29537 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1371,8 +1371,8 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
 	 * Note that the page can not be free in this function as call of
 	 * try_to_unmap() must hold a reference on the page.
 	 */
-	mmu_notifier_range_init(&range, vma->vm_mm, vma->vm_start,
-				min(vma->vm_end, vma->vm_start +
+	mmu_notifier_range_init(&range, vma->vm_mm, address,
+				min(vma->vm_end, address +
 				    (PAGE_SIZE << compound_order(page))));
 	if (PageHuge(page)) {
 		/*
-- 
2.19.2