linux-kernel - [RFC PATCH 1/3] KVM: arm64: Fix possible memory leak in kvm stage2

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Date:   Mon, 30 Nov 2020 20:18:45 +0800
From:   Yanan Wang <wangyanan55@...wei.com>
To:     <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        Marc Zyngier <maz@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        James Morse <james.morse@....com>,
        "Julien Thierry" <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Gavin Shan <gshan@...hat.com>,
        Quentin Perret <qperret@...gle.com>
CC:     <wanghaibin.wang@...wei.com>, <yezengruan@...wei.com>,
        <zhukeqian1@...wei.com>, <yuzenghui@...wei.com>,
        <jiangkunkun@...wei.com>, <wangjingyi11@...wei.com>,
        <lushenming@...wei.com>, Yanan Wang <wangyanan55@...wei.com>
Subject: [RFC PATCH 1/3] KVM: arm64: Fix possible memory leak in kvm stage2

When installing a new leaf pte onto an invalid ptep, we need to get_page(ptep).
When just updating a valid leaf ptep, we shouldn't get_page(ptep).
Incorrect page_count of translation tables might lead to memory leak,
when unmapping a stage 2 memory range.

Signed-off-by: Yanan Wang <wangyanan55@...wei.com>
---
 arch/arm64/kvm/hyp/pgtable.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 0271b4a3b9fe..696b6aa83faf 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -186,6 +186,7 @@ static bool kvm_set_valid_leaf_pte(kvm_pte_t *ptep, u64 pa, kvm_pte_t attr,
 		return old == pte;
 
 	smp_store_release(ptep, pte);
+	get_page(virt_to_page(ptep));
 	return true;
 }
 
@@ -476,6 +477,7 @@ static bool stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level,
 	/* There's an existing valid leaf entry, so perform break-before-make */
 	kvm_set_invalid_pte(ptep);
 	kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, data->mmu, addr, level);
+	put_page(virt_to_page(ptep));
 	kvm_set_valid_leaf_pte(ptep, phys, data->attr, level);
 out:
 	data->phys += granule;
@@ -512,7 +514,7 @@ static int stage2_map_walk_leaf(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
 	}
 
 	if (stage2_map_walker_try_leaf(addr, end, level, ptep, data))
-		goto out_get_page;
+		return 0;
 
 	if (WARN_ON(level == KVM_PGTABLE_MAX_LEVELS - 1))
 		return -EINVAL;
@@ -536,9 +538,8 @@ static int stage2_map_walk_leaf(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
 	}
 
 	kvm_set_table_pte(ptep, childp);
-
-out_get_page:
 	get_page(page);
+
 	return 0;
 }
 
-- 
2.19.1