linux-kernel - Re: [RFC PATCH v3 4/6] crypto: ccp - check whether PSP supports SEV or TEE before initialization

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Date:   Thu, 19 Dec 2019 16:56:52 -0600
From:   Gary R Hook <gary.hook@....com>
To:     Rijo Thomas <Rijo-john.Thomas@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S . Miller" <davem@...emloft.net>,
        linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org
Cc:     Nimesh Easow <Nimesh.Easow@....com>,
        Devaraj Rangasamy <Devaraj.Rangasamy@....com>,
        Jens Wiklander <jens.wiklander@...aro.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: [RFC PATCH v3 4/6] crypto: ccp - check whether PSP supports SEV
 or TEE before initialization

On 12/4/19 12:19 AM, Rijo Thomas wrote:
> Read PSP feature register to check for TEE (Trusted Execution Environment)
> support.
> 
> If neither SEV nor TEE is supported by PSP, then skip PSP initialization.
> 
> Cc: Tom Lendacky <thomas.lendacky@....com>
> Cc: Jens Wiklander <jens.wiklander@...aro.org>
> Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> Co-developed-by: Devaraj Rangasamy <Devaraj.Rangasamy@....com>
> Signed-off-by: Devaraj Rangasamy <Devaraj.Rangasamy@....com>
> Signed-off-by: Rijo Thomas <Rijo-john.Thomas@....com>

Acked-by: Gary R Hook <gary.hook@....com>

> ---
>   drivers/crypto/ccp/psp-dev.c | 46 +++++++++++++++++++++++++++++++++++++++-----
>   1 file changed, 41 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/crypto/ccp/psp-dev.c b/drivers/crypto/ccp/psp-dev.c
> index 2cd7a5e..3bedf72 100644
> --- a/drivers/crypto/ccp/psp-dev.c
> +++ b/drivers/crypto/ccp/psp-dev.c
> @@ -53,7 +53,7 @@ static irqreturn_t psp_irq_handler(int irq, void *data)
>   	return IRQ_HANDLED;
>   }
>   
> -static int psp_check_sev_support(struct psp_device *psp)
> +static unsigned int psp_get_capability(struct psp_device *psp)
>   {
>   	unsigned int val = ioread32(psp->io_regs + psp->vdata->feature_reg);
>   
> @@ -66,11 +66,17 @@ static int psp_check_sev_support(struct psp_device *psp)
>   	 */
>   	if (val == 0xffffffff) {
>   		dev_notice(psp->dev, "psp: unable to access the device: you might be running a broken BIOS.\n");
> -		return -ENODEV;
> +		return 0;
>   	}
>   
> -	if (!(val & 1)) {
> -		/* Device does not support the SEV feature */
> +	return val;
> +}
> +
> +static int psp_check_sev_support(struct psp_device *psp,
> +				 unsigned int capability)
> +{
> +	/* Check if device supports SEV feature */
> +	if (!(capability & 1)) {
>   		dev_dbg(psp->dev, "psp does not support SEV\n");
>   		return -ENODEV;
>   	}
> @@ -78,10 +84,36 @@ static int psp_check_sev_support(struct psp_device *psp)
>   	return 0;
>   }
>   
> +static int psp_check_tee_support(struct psp_device *psp,
> +				 unsigned int capability)
> +{
> +	/* Check if device supports TEE feature */
> +	if (!(capability & 2)) {
> +		dev_dbg(psp->dev, "psp does not support TEE\n");
> +		return -ENODEV;
> +	}
> +
> +	return 0;
> +}
> +
> +static int psp_check_support(struct psp_device *psp,
> +			     unsigned int capability)
> +{
> +	int sev_support = psp_check_sev_support(psp, capability);
> +	int tee_support = psp_check_tee_support(psp, capability);
> +
> +	/* Return error if device neither supports SEV nor TEE */
> +	if (sev_support && tee_support)
> +		return -ENODEV;
> +
> +	return 0;
> +}
> +
>   int psp_dev_init(struct sp_device *sp)
>   {
>   	struct device *dev = sp->dev;
>   	struct psp_device *psp;
> +	unsigned int capability;
>   	int ret;
>   
>   	ret = -ENOMEM;
> @@ -100,7 +132,11 @@ int psp_dev_init(struct sp_device *sp)
>   
>   	psp->io_regs = sp->io_map;
>   
> -	ret = psp_check_sev_support(psp);
> +	capability = psp_get_capability(psp);
> +	if (!capability)
> +		goto e_disable;
> +
> +	ret = psp_check_support(psp, capability);
>   	if (ret)
>   		goto e_disable;
>   
>