linux-kernel - Re: [PATCH v2 16/16] arm64: Add ARM_SMCCC_ARCH_WORKAROUND

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Date:   Wed, 31 Jan 2018 21:56:10 +0800
From:   Hanjun Guo <guohanjun@...wei.com>
To:     Marc Zyngier <marc.zyngier@....com>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <kvmarm@...ts.cs.columbia.edu>
CC:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Peter Maydell <peter.maydell@...aro.org>,
        "Christoffer Dall" <christoffer.dall@...aro.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Mark Rutland <mark.rutland@....com>,
        "Robin Murphy" <robin.murphy@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Jon Masters <jcm@...hat.com>
Subject: Re: [PATCH v2 16/16] arm64: Add ARM_SMCCC_ARCH_WORKAROUND_1 BP
 hardening support

Hi Marc,

On 2018/1/30 1:45, Marc Zyngier wrote:
>  static int enable_psci_bp_hardening(void *data)
>  {
>  	const struct arm64_cpu_capabilities *entry = data;
>  
> -	if (psci_ops.get_version)
> +	if (psci_ops.get_version) {
> +		if (check_smccc_arch_workaround_1(entry))
> +			return 0;

If I'm using the new version SMCCC, the firmware have the choice to decide
whether this machine needs the workaround, even if the CPU is vulnerable
for CVE-2017-5715, but..

> +
>  		install_bp_hardening_cb(entry,
>  				       (bp_hardening_cb_t)psci_ops.get_version,
>  				       __psci_hyp_bp_inval_start,
>  				       __psci_hyp_bp_inval_end);

..the code above seems will enable get_psci_version() for CPU and will
trap to trust firmware even the new version of firmware didn't say
we need the workaround, did I understand it correctly?

I'm ask this because some platform will not expose to users to
take advantage of CVE-2017-5715, and we can use different firmware
to report we need such workaround or not, then use a single kernel
image for both vulnerable platforms and no vulnerable ones.

Thanks
Hanjun