linux-kernel - [PATCH 5.15 036/136] mm/smaps: dont access young/dirty bit if pte unpresent

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Date:   Mon, 29 Aug 2022 12:58:23 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Peter Xu <peterx@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Hildenbrand <david@...hat.com>,
        Yang Shi <shy828301@...il.com>,
        Konstantin Khlebnikov <khlebnikov@...nvz.org>,
        Huang Ying <ying.huang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.15 036/136] mm/smaps: dont access young/dirty bit if pte unpresent

From: Peter Xu <peterx@...hat.com>

[ Upstream commit efd4149342db2df41b1bbe68972ead853b30e444 ]

These bits should only be valid when the ptes are present.  Introducing
two booleans for it and set it to false when !pte_present() for both pte
and pmd accountings.

The bug is found during code reading and no real world issue reported, but
logically such an error can cause incorrect readings for either smaps or
smaps_rollup output on quite a few fields.

For example, it could cause over-estimate on values like Shared_Dirty,
Private_Dirty, Referenced.  Or it could also cause under-estimate on
values like LazyFree, Shared_Clean, Private_Clean.

Link: https://lkml.kernel.org/r/20220805160003.58929-1-peterx@redhat.com
Fixes: b1d4d9e0cbd0 ("proc/smaps: carefully handle migration entries")
Fixes: c94b6923fa0a ("/proc/PID/smaps: Add PMD migration entry parsing")
Signed-off-by: Peter Xu <peterx@...hat.com>
Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
Reviewed-by: David Hildenbrand <david@...hat.com>
Reviewed-by: Yang Shi <shy828301@...il.com>
Cc: Konstantin Khlebnikov <khlebnikov@...nvz.org>
Cc: Huang Ying <ying.huang@...el.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/proc/task_mmu.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 79ca4d69dfd6b..d9c07eecd7872 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -503,10 +503,12 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
 	struct vm_area_struct *vma = walk->vma;
 	bool locked = !!(vma->vm_flags & VM_LOCKED);
 	struct page *page = NULL;
-	bool migration = false;
+	bool migration = false, young = false, dirty = false;
 
 	if (pte_present(*pte)) {
 		page = vm_normal_page(vma, addr, *pte);
+		young = pte_young(*pte);
+		dirty = pte_dirty(*pte);
 	} else if (is_swap_pte(*pte)) {
 		swp_entry_t swpent = pte_to_swp_entry(*pte);
 
@@ -540,8 +542,7 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
 	if (!page)
 		return;
 
-	smaps_account(mss, page, false, pte_young(*pte), pte_dirty(*pte),
-		      locked, migration);
+	smaps_account(mss, page, false, young, dirty, locked, migration);
 }
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-- 
2.35.1