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Message-ID: <87v7lyzhoj.wl-maz@kernel.org>
Date: Thu, 04 Sep 2025 10:32:44 +0100
From: Marc Zyngier <maz@...nel.org>
To: Geonha Lee <w1nsom3gna@...ea.ac.kr>
Cc: kvmarm@...ts.linux.dev,
linux-arm-kernel@...ts.infradead.org,
linux-kernel@...r.kernel.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>
Subject: Re: [PATCH] KVM: arm64: nested: fix VNCR TLB ASID match logic for non-Global entries
On Wed, 03 Sep 2025 16:04:21 +0100,
Geonha Lee <w1nsom3gna@...ea.ac.kr> wrote:
>
> 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.
I don't immediately see the vulnerability on the host. In the guest,
yes, absolutely.
>
> 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)
Reported-by: has a specific meaning, and needs addresses. Oliver, can
you change this to some sort of attribution?
>
> 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;
Yup, looks correct to me. Thanks again for fixing it.
Reviewed-by: Marc Zyngier <maz@...nel.org>
M.
--
Jazz isn't dead. It just smells funny.
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