linux-kernel - Re: [PATCH v3 32/32] KVM: arm64: Protect the .hyp sections from the host

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Message-ID: <20210305191327.GD23633@willie-the-truck>
Date:   Fri, 5 Mar 2021 19:13:27 +0000
From:   Will Deacon <will@...nel.org>
To:     Quentin Perret <qperret@...gle.com>
Cc:     catalin.marinas@....com, maz@...nel.org, james.morse@....com,
        julien.thierry.kdev@...il.com, suzuki.poulose@....com,
        android-kvm@...gle.com, linux-kernel@...r.kernel.org,
        kernel-team@...roid.com, kvmarm@...ts.cs.columbia.edu,
        linux-arm-kernel@...ts.infradead.org, tabba@...gle.com,
        mark.rutland@....com, dbrazdil@...gle.com, mate.toth-pal@....com,
        seanjc@...gle.com, robh+dt@...nel.org
Subject: Re: [PATCH v3 32/32] KVM: arm64: Protect the .hyp sections from the
 host

On Tue, Mar 02, 2021 at 03:00:02PM +0000, Quentin Perret wrote:
> When KVM runs in nVHE protected mode, use the host stage 2 to unmap the
> hypervisor sections. The long-term goal is to ensure the EL2 code can
> remain robust regardless of the host's state, so this starts by making
> sure the host cannot e.g. write to the .hyp sections directly.
> 
> Signed-off-by: Quentin Perret <qperret@...gle.com>
> ---
>  arch/arm64/include/asm/kvm_asm.h              |  1 +
>  arch/arm64/kvm/arm.c                          | 46 +++++++++++++++++++
>  arch/arm64/kvm/hyp/include/nvhe/mem_protect.h |  2 +
>  arch/arm64/kvm/hyp/nvhe/hyp-main.c            |  9 ++++
>  arch/arm64/kvm/hyp/nvhe/mem_protect.c         | 22 +++++++++
>  5 files changed, 80 insertions(+)

[...]

>  static void handle_host_hcall(struct kvm_cpu_context *host_ctxt)
> diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> index 2252ad1a8945..ed480facdc88 100644
> --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
> @@ -196,6 +196,28 @@ static int host_stage2_idmap(u64 addr)
>  	return ret;
>  }
>  
> +int __pkvm_host_unmap(phys_addr_t start, phys_addr_t end)
> +{
> +	struct kvm_mem_range r1, r2;
> +	int ret;
> +
> +	/*
> +	 * host_stage2_unmap_dev_all() currently relies on MMIO mappings being
> +	 * non-persistent, so don't allow PROT_NONE in MMIO range.
> +	 */
> +	if (!find_mem_range(start, &r1) || !find_mem_range(end, &r2))
> +		return -EINVAL;
> +	if (r1.start != r2.start)
> +		return -EINVAL;


Feels like this should be in a helper to determine whether or not a range is
solely covered by memory.

Either way:

Acked-by: Will Deacon <will@...nel.org>

Will