linux-kernel - [PATCH v2] mm/smaps: Don't access young/dirty bit if pte unpresent

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Date:   Fri,  5 Aug 2022 12:00:03 -0400
From:   Peter Xu <peterx@...hat.com>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     Yang Shi <shy828301@...il.com>,
        David Hildenbrand <david@...hat.com>, peterx@...hat.com,
        Nadav Amit <nadav.amit@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Konstantin Khlebnikov <khlebnikov@...nvz.org>,
        Huang Ying <ying.huang@...el.com>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH v2] mm/smaps: Don't access young/dirty bit if pte unpresent

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.

Cc: Konstantin Khlebnikov <khlebnikov@...nvz.org>
Cc: Huang Ying <ying.huang@...el.com>
Fixes: b1d4d9e0cbd0 ("proc/smaps: carefully handle migration entries")
Fixes: c94b6923fa0a ("/proc/PID/smaps: Add PMD migration entry parsing")
Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
Reviewed-by: David Hildenbrand <david@...hat.com>
Reviewed-by: Yang Shi <shy828301@...il.com>
Signed-off-by: Peter Xu <peterx@...hat.com>
---
 fs/proc/task_mmu.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 9913f3be9fd2..d56c65f98d00 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -527,10 +527,12 @@ 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);
 
@@ -560,8 +562,7 @@ 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
@@ -572,11 +573,13 @@ static void smaps_pmd_entry(pmd_t *pmd, 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 (pmd_present(*pmd)) {
 		/* FOLL_DUMP will return -EFAULT on huge zero page */
 		page = follow_trans_huge_pmd(vma, addr, pmd, FOLL_DUMP);
+		young = pmd_young(*pmd);
+		dirty = pmd_dirty(*pmd);
 	} else if (unlikely(thp_migration_supported() && is_swap_pmd(*pmd))) {
 		swp_entry_t entry = pmd_to_swp_entry(*pmd);
 
@@ -596,8 +599,7 @@ static void smaps_pmd_entry(pmd_t *pmd, unsigned long addr,
 	else
 		mss->file_thp += HPAGE_PMD_SIZE;
 
-	smaps_account(mss, page, true, pmd_young(*pmd), pmd_dirty(*pmd),
-		      locked, migration);
+	smaps_account(mss, page, true, young, dirty, locked, migration);
 }
 #else
 static void smaps_pmd_entry(pmd_t *pmd, unsigned long addr,
-- 
2.32.0