linux-kernel - [PATCH] kasan: fix unaligned address is unhandled in kasan_remove_zero

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Date:   Sun,  3 Jan 2021 21:56:21 +0800
From:   Lecopzer Chen <lecopzer@...il.com>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        kasan-dev@...glegroups.com
Cc:     dan.j.williams@...el.com, aryabinin@...tuozzo.com,
        glider@...gle.com, dvyukov@...gle.com, akpm@...ux-foundation.org,
        linux-mediatek@...ts.infradead.org, yj.chiang@...iatek.com,
        Lecopzer Chen <lecopzer@...il.com>,
        Lecopzer Chen <lecopzer.chen@...iatek.com>
Subject: [PATCH] kasan: fix unaligned address is unhandled in kasan_remove_zero_shadow

During testing kasan_populate_early_shadow and kasan_remove_zero_shadow,
if the shadow start and end address in kasan_remove_zero_shadow() is
not aligned to PMD_SIZE, the remain unaligned PTE won't be removed.

In the test case for kasan_remove_zero_shadow():
    shadow_start: 0xffffffb802000000, shadow end: 0xffffffbfbe000000
    3-level page table:
      PUD_SIZE: 0x40000000 PMD_SIZE: 0x200000 PAGE_SIZE: 4K
0xffffffbf80000000 ~ 0xffffffbfbdf80000 will not be removed because
in kasan_remove_pud_table(), kasan_pmd_table(*pud) is true but the
next address is 0xffffffbfbdf80000 which is not aligned to PUD_SIZE.

In the correct condition, this should fallback to the next level
kasan_remove_pmd_table() but the condition flow always continue to skip
the unaligned part.

Fix by correcting the condition when next and addr are neither aligned.

Fixes: 0207df4fa1a86 ("kernel/memremap, kasan: make ZONE_DEVICE with work with KASAN")
Signed-off-by: Lecopzer Chen <lecopzer.chen@...iatek.com>
---
 mm/kasan/init.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/mm/kasan/init.c b/mm/kasan/init.c
index 67051cfae41c..ae9158f7501f 100644
--- a/mm/kasan/init.c
+++ b/mm/kasan/init.c
@@ -372,9 +372,10 @@ static void kasan_remove_pmd_table(pmd_t *pmd, unsigned long addr,
 
 		if (kasan_pte_table(*pmd)) {
 			if (IS_ALIGNED(addr, PMD_SIZE) &&
-			    IS_ALIGNED(next, PMD_SIZE))
+			    IS_ALIGNED(next, PMD_SIZE)) {
 				pmd_clear(pmd);
-			continue;
+				continue;
+			}
 		}
 		pte = pte_offset_kernel(pmd, addr);
 		kasan_remove_pte_table(pte, addr, next);
@@ -397,9 +398,10 @@ static void kasan_remove_pud_table(pud_t *pud, unsigned long addr,
 
 		if (kasan_pmd_table(*pud)) {
 			if (IS_ALIGNED(addr, PUD_SIZE) &&
-			    IS_ALIGNED(next, PUD_SIZE))
+			    IS_ALIGNED(next, PUD_SIZE)) {
 				pud_clear(pud);
-			continue;
+				continue;
+			}
 		}
 		pmd = pmd_offset(pud, addr);
 		pmd_base = pmd_offset(pud, 0);
@@ -423,9 +425,10 @@ static void kasan_remove_p4d_table(p4d_t *p4d, unsigned long addr,
 
 		if (kasan_pud_table(*p4d)) {
 			if (IS_ALIGNED(addr, P4D_SIZE) &&
-			    IS_ALIGNED(next, P4D_SIZE))
+			    IS_ALIGNED(next, P4D_SIZE)) {
 				p4d_clear(p4d);
-			continue;
+				continue;
+			}
 		}
 		pud = pud_offset(p4d, addr);
 		kasan_remove_pud_table(pud, addr, next);
@@ -456,9 +459,10 @@ void kasan_remove_zero_shadow(void *start, unsigned long size)
 
 		if (kasan_p4d_table(*pgd)) {
 			if (IS_ALIGNED(addr, PGDIR_SIZE) &&
-			    IS_ALIGNED(next, PGDIR_SIZE))
+			    IS_ALIGNED(next, PGDIR_SIZE)) {
 				pgd_clear(pgd);
-			continue;
+				continue;
+			}
 		}
 
 		p4d = p4d_offset(pgd, addr);
-- 
2.25.1