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From: Oliver Upton <oliver.upton@linux.dev>
To: Marc Zyngier <maz@kernel.org>, James Morse <james.morse@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Oliver Upton <oliver.upton@linux.dev>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org,
	kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: [PATCH v4 3/3] KVM: arm64: Reject shared table walks in the hyp code
Date: Fri, 18 Nov 2022 18:22:22 +0000	[thread overview]
Message-ID: <20221118182222.3932898-4-oliver.upton@linux.dev> (raw)
In-Reply-To: <20221118182222.3932898-1-oliver.upton@linux.dev>

Exclusive table walks are the only supported table walk in the hyp, as
there is no construct like RCU available in the hypervisor code. Reject
any attempt to do a shared table walk by returning an error and allowing
the caller to clean up the mess.

Suggested-by: Will Deacon <will@kernel.org>
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/include/asm/kvm_pgtable.h | 17 +++++++++++++++--
 arch/arm64/kvm/hyp/pgtable.c         |  5 ++++-
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index 4b6b52ebc11c..d5cb01f8dc06 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -229,7 +229,18 @@ static inline kvm_pte_t *kvm_dereference_pteref(struct kvm_pgtable_walker *walke
 	return pteref;
 }
 
-static inline void kvm_pgtable_walk_begin(struct kvm_pgtable_walker *walker) {}
+static inline int kvm_pgtable_walk_begin(struct kvm_pgtable_walker *walker)
+{
+	/*
+	 * Due to the lack of RCU (or a similar protection scheme), only
+	 * non-shared table walkers are allowed in the hypervisor.
+	 */
+	if (walker->flags & KVM_PGTABLE_WALK_SHARED)
+		return -EPERM;
+
+	return 0;
+}
+
 static inline void kvm_pgtable_walk_end(struct kvm_pgtable_walker *walker) {}
 
 static inline bool kvm_pgtable_walk_lock_held(void)
@@ -247,10 +258,12 @@ static inline kvm_pte_t *kvm_dereference_pteref(struct kvm_pgtable_walker *walke
 	return rcu_dereference_check(pteref, !(walker->flags & KVM_PGTABLE_WALK_SHARED));
 }
 
-static inline void kvm_pgtable_walk_begin(struct kvm_pgtable_walker *walker)
+static inline int kvm_pgtable_walk_begin(struct kvm_pgtable_walker *walker)
 {
 	if (walker->flags & KVM_PGTABLE_WALK_SHARED)
 		rcu_read_lock();
+
+	return 0;
 }
 
 static inline void kvm_pgtable_walk_end(struct kvm_pgtable_walker *walker)
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index d6f3753cb87e..58dbe0ab567f 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -289,7 +289,10 @@ int kvm_pgtable_walk(struct kvm_pgtable *pgt, u64 addr, u64 size,
 	};
 	int r;
 
-	kvm_pgtable_walk_begin(walker);
+	r = kvm_pgtable_walk_begin(walker);
+	if (r)
+		return r;
+
 	r = _kvm_pgtable_walk(pgt, &walk_data);
 	kvm_pgtable_walk_end(walker);
 
-- 
2.38.1.584.g0f3c55d4c2-goog


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  parent reply	other threads:[~2022-11-18 18:24 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-18 18:22 [PATCH v4 0/3] KVM: arm64: Fixes for parallel faults series Oliver Upton
2022-11-18 18:22 ` [PATCH v4 1/3] KVM: arm64: Take a pointer to walker data in kvm_dereference_pteref() Oliver Upton
2022-11-18 18:22 ` [PATCH v4 2/3] KVM: arm64: Don't acquire RCU read lock for exclusive table walks Oliver Upton
2022-11-18 18:22 ` Oliver Upton [this message]
2022-11-21 18:09 ` [PATCH v4 0/3] KVM: arm64: Fixes for parallel faults series Will Deacon
2022-11-22 13:09 ` Marc Zyngier

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