Re: [PATCH 4/8] platform/x86/amd/pmf: Get policy binary signature size from PSP header

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

On Sun, 11 Oct 2026, Shyam Sundar S K wrote:

> The policy binary size is calculated as the payload length plus a fixed
> 512 bytes, which assumes a 256 byte PSP header and a 256 byte RSA2K
> signature. Newer policy binaries can be signed with RSA4K, which has a
> 512 byte signature.
> 
> Read the signature algorithm from the PSP header and use it to get the
> signature size. Check that the buffer is large enough before reading
> the header field, and that the size calculation does not overflow.
> 
> Policy binaries with an unknown signature algorithm are now rejected.
> 
> Co-developed-by: Patil Rajesh Reddy <Patil.Reddy@amd.com>
> Signed-off-by: Patil Rajesh Reddy <Patil.Reddy@amd.com>
> Signed-off-by: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
> ---
>  drivers/platform/x86/amd/pmf/pmf.h    |  8 +++++++
>  drivers/platform/x86/amd/pmf/tee-if.c | 34 +++++++++++++++++++++++++--
>  2 files changed, 40 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/platform/x86/amd/pmf/pmf.h b/drivers/platform/x86/amd/pmf/pmf.h
> index d9fa99c2750f..86999802602c 100644
> --- a/drivers/platform/x86/amd/pmf/pmf.h
> +++ b/drivers/platform/x86/amd/pmf/pmf.h
> @@ -29,6 +29,14 @@
>  #define POLICY_SIGN_COOKIE		0x31535024
>  #define POLICY_COOKIE_OFFSET		0x10
>  
> +/* Policy binary PSP header */
> +#define POLICY_PSP_HEADER_SIZE		256
> +#define POLICY_PSP_SIG_ALG_OFFSET	0x34
> +#define POLICY_PSP_SIG_ALG_RSA2K	0
> +#define POLICY_PSP_SIG_ALG_RSA4K	2
> +#define POLICY_PSP_SIG_SIZE_RSA2K	256
> +#define POLICY_PSP_SIG_SIZE_RSA4K	512

SZ_* x3

-- 
 i.

> +
>  /* List of supported CPU ids */
>  #define AMD_CPU_ID_RMB                  0x14b5
>  #define AMD_CPU_ID_PS                   0x14e8
> diff --git a/drivers/platform/x86/amd/pmf/tee-if.c b/drivers/platform/x86/amd/pmf/tee-if.c
> index e145eb7b03cd..9b328be1e8f4 100644
> --- a/drivers/platform/x86/amd/pmf/tee-if.c
> +++ b/drivers/platform/x86/amd/pmf/tee-if.c
> @@ -11,7 +11,9 @@
>  #include <linux/array_size.h>
>  #include <linux/debugfs.h>
>  #include <linux/dev_printk.h>
> +#include <linux/overflow.h>
>  #include <linux/tee_drv.h>
> +#include <linux/unaligned.h>
>  #include <linux/uuid.h>
>  #include "pmf.h"
>  
> @@ -327,9 +329,32 @@ static void amd_pmf_invoke_cmd(struct work_struct *work)
>  	schedule_delayed_work(&dev->pb_work, msecs_to_jiffies(pb_actions_ms));
>  }
>  
> +static int amd_pmf_get_pb_sig_size(struct amd_pmf_dev *dev, u32 *sig_size)
> +{
> +	u32 sig_alg;
> +
> +	if (dev->policy_sz < POLICY_PSP_SIG_ALG_OFFSET + sizeof(sig_alg))
> +		return -EINVAL;
> +
> +	sig_alg = get_unaligned_le32(dev->policy_buf + POLICY_PSP_SIG_ALG_OFFSET);
> +
> +	switch (sig_alg) {
> +	case POLICY_PSP_SIG_ALG_RSA2K:
> +		*sig_size = POLICY_PSP_SIG_SIZE_RSA2K;
> +		return 0;
> +	case POLICY_PSP_SIG_ALG_RSA4K:
> +		*sig_size = POLICY_PSP_SIG_SIZE_RSA4K;
> +		return 0;
> +	default:
> +		dev_dbg(dev->dev, "Unknown PSP signature algorithm: %u\n", sig_alg);
> +		return -EINVAL;
> +	}
> +}
> +
>  int amd_pmf_start_policy_engine(struct amd_pmf_dev *dev)
>  {
>  	struct cookie_header *header;
> +	u32 sig_size, total_sz;
>  	int res;
>  
>  	if (dev->policy_sz < POLICY_COOKIE_OFFSET + sizeof(*header))
> @@ -342,11 +367,16 @@ int amd_pmf_start_policy_engine(struct amd_pmf_dev *dev)
>  		return -EINVAL;
>  	}
>  
> -	if (dev->policy_sz < header->length + 512)
> +	res = amd_pmf_get_pb_sig_size(dev, &sig_size);
> +	if (res)
> +		return res;
> +
> +	if (check_add_overflow(header->length, POLICY_PSP_HEADER_SIZE + sig_size, &total_sz) ||
> +	    dev->policy_sz < total_sz)
>  		return -EINVAL;
>  
>  	/* Update the actual length */
> -	dev->policy_sz = header->length + 512;
> +	dev->policy_sz = total_sz;
>  	res = dev->ta_ops->invoke_init(dev);
>  	if (res == TA_PMF_TYPE_SUCCESS) {
>  		/* Now its safe to announce that smart pc is enabled */
>