linux-kernel - [PATCH] KVM: arm64: nested: fix VNCR TLB ASID match logic for non-Global entries

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Message-ID: <20250903150421.90752-1-w1nsom3gna@korea.ac.kr>
Date: Thu,  4 Sep 2025 00:04:21 +0900
From: Geonha Lee <w1nsom3gna@...ea.ac.kr>
To: kvmarm@...ts.linux.dev
Cc: linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Marc Zyngier <maz@...nel.org>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Geonha Lee <w1nsom3gna@...ea.ac.kr>
Subject: [PATCH] KVM: arm64: nested: fix VNCR TLB ASID match logic for non-Global entries

kvm_vncr_tlb_lookup() is supposed to return true when the cached VNCR
TLB entry is valid for the current context. For non-Global entries, that
means the entry’s ASID must match the current ASID.

The current code returns true when the ASIDs do *not* match, which
inverts the logic. This is a potential vulnerability:

- Valid entries are ignored and we fall back to kvm_translate_vncr(),
  hurting performance.
- Mismatched entries are treated as permission faults (-EPERM) instead
  of triggering a fresh translation.
- This can also cause stale translations to be (wrongly) considered
  valid across address spaces.

Flip the predicate so non-Global entries only hit when ASIDs match.

Reported-by: Team 0xB6 in bob14
  DongHa Lee (@GAP-dev)
  Gyujeong Jin (@gyutrange)
  Daehyeon Ko (@4ncienth)
  Geonha Lee (@leegn4a)
  Hyungyu Oh (@DQPC_lover)
  Jaewon Yang (@R4mbb)

Signed-off-by: Geonha Lee <w1nsom3gna@...ea.ac.kr>
---
 arch/arm64/kvm/nested.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c
index 77db81bae86f..24eab94d7d7f 100644
--- a/arch/arm64/kvm/nested.c
+++ b/arch/arm64/kvm/nested.c
@@ -1276,7 +1276,7 @@ static bool kvm_vncr_tlb_lookup(struct kvm_vcpu *vcpu)
 		    !(tcr & TCR_ASID16))
 			asid &= GENMASK(7, 0);
 
-		return asid != vt->wr.asid;
+		return asid == vt->wr.asid;
 	}
 
 	return true;
-- 
2.43.0