Re: [PATCH Part1 v5 35/38] x86/sev: Register SNP guest request platform device

Dov Murik
2021-08-31T11:39:16Z

Hi Brijesh,

On 20/08/2021 18:19, Brijesh Singh wrote:
> Version 2 of GHCB specification provides NAEs that can be used by the SNP
> guest to communicate with the PSP without risk from a malicious hypervisor
> who wishes to read, alter, drop or replay the messages sent.
>
> In order to communicate with the PSP, the guest need to locate the secrets
> page inserted by the hypervisor during the SEV-SNP guest launch. The
> secrets page contains the communication keys used to send and receive the
> encrypted messages between the guest and the PSP. The secrets page location
> is passed through the setup_data.
>
> Create a platform device that the SNP guest driver can bind to get the
> platform resources such as encryption key and message id to use to
> communicate with the PSP. The SNP guest driver can provide userspace
> interface to get the attestation report, key derivation, extended
> attestation report etc.
>
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> ---
> arch/x86/kernel/sev.c | 68 +++++++++++++++++++++++++++++++++++++++
> include/linux/sev-guest.h | 5 +++
> 2 files changed, 73 insertions(+)
>
> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> index f42cd5a8e7bb..ab17c93634e9 100644
> --- a/arch/x86/kernel/sev.c
> +++ b/arch/x86/kernel/sev.c
> @@ -22,6 +22,8 @@
> #include <linux/log2.h>
> #include <linux/efi.h>
> #include <linux/sev-guest.h>
> +#include <linux/platform_device.h>
> +#include <linux/io.h>
>
> #include <asm/cpu_entry_area.h>
> #include <asm/stacktrace.h>
> @@ -37,6 +39,7 @@
> #include <asm/apic.h>
> #include <asm/efi.h>
> #include <asm/cpuid.h>
> +#include <asm/setup.h>
>
> #include "sev-internal.h"
>
> @@ -2164,3 +2167,68 @@ int snp_issue_guest_request(int type, struct snp_guest_request_data *input, unsi
> return ret;
> }
> EXPORT_SYMBOL_GPL(snp_issue_guest_request);
> +
> +static struct platform_device guest_req_device = {
> + .name = "snp-guest",
> + .id = -1,
> +};
> +
> +static u64 find_secrets_paddr(void)
> +{
> + u64 pa_data = boot_params.cc_blob_address;
> + struct cc_blob_sev_info info;
> + void *map;
> +
> + /*
> + * The CC blob contains the address of the secrets page, check if the
> + * blob is present.
> + */
> + if (!pa_data)
> + return 0;
> +
> + map = early_memremap(pa_data, sizeof(info));
> + memcpy(&info, map, sizeof(info));
> + early_memunmap(map, sizeof(info));
> +
> + /* Verify that secrets page address is passed */
> + if (info.secrets_phys && info.secrets_len == PAGE_SIZE)
> + return info.secrets_phys;
> +
> + return 0;
> +}
> +
> +static int __init add_snp_guest_request(void)
> +{
> + struct snp_secrets_page_layout *layout;
> + struct snp_guest_platform_data data;
> +
> + if (!sev_feature_enabled(SEV_SNP))
> + return -ENODEV;
> +
> + snp_secrets_phys = find_secrets_paddr();
> + if (!snp_secrets_phys)
> + return -ENODEV;
> +
> + layout = snp_map_secrets_page();
> + if (!layout)
> + return -ENODEV;
> +
> + /*
> + * The secrets page contains three VMPCK that can be used for
> + * communicating with the PSP. We choose the VMPCK0 to encrypt guest
> + * messages send and receive by the Linux. Provide the key and
> + * id through the platform data to the driver.
> + */
> + data.vmpck_id = 0;
> + memcpy_fromio(data.vmpck, layout->vmpck0, sizeof(data.vmpck));
> +
> + iounmap(layout);
> +
> + platform_device_add_data(&guest_req_device, &data, sizeof(data));
> +
> + if (!platform_device_register(&guest_req_device))
> + dev_info(&guest_req_device.dev, "secret phys 0x%llx\n", snp_secrets_phys);

Should you return the error code from platform_device_register() in case
it fails (returns something other than zero)?

-Dov

> +
> + return 0;
> +}
> +device_initcall(add_snp_guest_request);
> diff --git a/include/linux/sev-guest.h b/include/linux/sev-guest.h
> index 16b6af24fda7..e1cb3f7dd034 100644
> --- a/include/linux/sev-guest.h
> +++ b/include/linux/sev-guest.h
> @@ -68,6 +68,11 @@ struct snp_guest_request_data {
> unsigned int data_npages;
> };
>
> +struct snp_guest_platform_data {
> + u8 vmpck_id;
> + char vmpck[VMPCK_KEY_LEN];
> +};
> +
> #ifdef CONFIG_AMD_MEM_ENCRYPT
> int snp_issue_guest_request(int vmgexit_type, struct snp_guest_request_data *input,
> unsigned long *fw_err);
>