linux-kernel - [PATCH] powerpc: Fix random segfault when freeing hugetlb range

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Message-Id: <f0cb2a5477cd87d1eaadb128042e20aeb2bc2859.1598860677.git.christophe.leroy@csgroup.eu>
Date:   Mon, 31 Aug 2020 07:58:19 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH] powerpc: Fix random segfault when freeing hugetlb range

The following random segfault is observed from time to time with
map_hugetlb selftest:

root@...alhost:~# ./map_hugetlb 1 19
524288 kB hugepages
Mapping 1 Mbytes
Segmentation fault

[   31.219972] map_hugetlb[365]: segfault (11) at 117 nip 77974f8c lr 779a6834 code 1 in ld-2.23.so[77966000+21000]
[   31.220192] map_hugetlb[365]: code: 9421ffc0 480318d1 93410028 90010044 9361002c 93810030 93a10034 93c10038
[   31.220307] map_hugetlb[365]: code: 93e1003c 93210024 8123007c 81430038 <80e90004> 814a0004 7f443a14 813a0004
[   31.221911] BUG: Bad rss-counter state mm:(ptrval) type:MM_FILEPAGES val:33
[   31.229362] BUG: Bad rss-counter state mm:(ptrval) type:MM_ANONPAGES val:5

This fault is due to hugetlb_free_pgd_range() freeing page tables
that are also used by regular pages.

As explain in the comment at the beginning of
hugetlb_free_pgd_range(), the verification done in free_pgd_range()
on floor and ceiling is not done here, which means
hugetlb_free_pte_range() can free outside the expected range.

As the verification cannot be done in hugetlb_free_pgd_range(), it
must be done in hugetlb_free_pte_range().

Fixes: b250c8c08c79 ("powerpc/8xx: Manage 512k huge pages as standard pages.")
Cc: stable@...r.kernel.org
Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/mm/hugetlbpage.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
index 26292544630f..e7ae2a2c4545 100644
--- a/arch/powerpc/mm/hugetlbpage.c
+++ b/arch/powerpc/mm/hugetlbpage.c
@@ -330,10 +330,24 @@ static void free_hugepd_range(struct mmu_gather *tlb, hugepd_t *hpdp, int pdshif
 				 get_hugepd_cache_index(pdshift - shift));
 }
 
-static void hugetlb_free_pte_range(struct mmu_gather *tlb, pmd_t *pmd, unsigned long addr)
+static void hugetlb_free_pte_range(struct mmu_gather *tlb, pmd_t *pmd,
+				   unsigned long addr, unsigned long end,
+				   unsigned long floor, unsigned long ceiling)
 {
+	unsigned long start = addr;
 	pgtable_t token = pmd_pgtable(*pmd);
 
+	start &= PMD_MASK;
+	if (start < floor)
+		return;
+	if (ceiling) {
+		ceiling &= PMD_MASK;
+		if (!ceiling)
+			return;
+	}
+	if (end - 1 > ceiling - 1)
+		return;
+
 	pmd_clear(pmd);
 	pte_free_tlb(tlb, token, addr);
 	mm_dec_nr_ptes(tlb->mm);
@@ -363,7 +377,7 @@ static void hugetlb_free_pmd_range(struct mmu_gather *tlb, pud_t *pud,
 			 */
 			WARN_ON(!IS_ENABLED(CONFIG_PPC_8xx));
 
-			hugetlb_free_pte_range(tlb, pmd, addr);
+			hugetlb_free_pte_range(tlb, pmd, addr, end, floor, ceiling);
 
 			continue;
 		}
-- 
2.25.0