Re: [PATCH Part1 RFC v3 21/22] x86/sev: Register SNP guest request platform device

Dr. David Alan Gilbert
2021-06-09T19:25:13Z

* Brijesh Singh (brijesh.singh@amd.com) 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.
>
> The hypervisor uses the SNP_GUEST_REQUEST command interface provided by
> the SEV-SNP firmware to forward the guest messages to the PSP.
>
> 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 is located either through the setup_data cc_blob_address
> or EFI configuration table.
>
> Create a platform device that the SNP guest driver can bind to get the
> platform resources. The SNP guest driver can provide userspace interface
> to get the attestation report, key derivation etc.
>
> The helper snp_issue_guest_request() will be used by the drivers to
> send the guest message request to the hypervisor. The guest message header
> contains a message count. The message count is used in the IV. The
> firmware increments the message count by 1, and expects that next message
> will be using the incremented count.
>
> The helper snp_msg_seqno() will be used by driver to get and message
> sequence counter, and it will be automatically incremented by the
> snp_issue_guest_request(). The incremented value is be saved in the
> secrets page so that the kexec'ed kernel knows from where to begin.
>
> See SEV-SNP and GHCB spec for more details.
>
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> ---
> arch/x86/include/asm/sev.h | 12 +++
> arch/x86/include/uapi/asm/svm.h | 2 +
> arch/x86/kernel/sev.c | 176 ++++++++++++++++++++++++++++++++
> arch/x86/platform/efi/efi.c | 2 +
> include/linux/efi.h | 1 +
> include/linux/sev-guest.h | 76 ++++++++++++++
> 6 files changed, 269 insertions(+)
> create mode 100644 include/linux/sev-guest.h
>
> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> index 640108402ae9..da2f757cd9bc 100644
> --- a/arch/x86/include/asm/sev.h
> +++ b/arch/x86/include/asm/sev.h
> @@ -59,6 +59,18 @@ extern void vc_no_ghcb(void);
> extern void vc_boot_ghcb(void);
> extern bool handle_vc_boot_ghcb(struct pt_regs *regs);
>
> +/* AMD SEV Confidential computing blob structure */
> +#define CC_BLOB_SEV_HDR_MAGIC 0x45444d41
> +struct cc_blob_sev_info {
> + u32 magic;
> + u16 version;
> + u16 reserved;
> + u64 secrets_phys;
> + u32 secrets_len;
> + u64 cpuid_phys;
> + u32 cpuid_len;
> +};
> +
> /* Software defined (when rFlags.CF = 1) */
> #define PVALIDATE_FAIL_NOUPDATE 255
>
> diff --git a/arch/x86/include/uapi/asm/svm.h b/arch/x86/include/uapi/asm/svm.h
> index c0152186a008..bd64f2b98ac7 100644
> --- a/arch/x86/include/uapi/asm/svm.h
> +++ b/arch/x86/include/uapi/asm/svm.h
> @@ -109,6 +109,7 @@
> #define SVM_VMGEXIT_SET_AP_JUMP_TABLE 0
> #define SVM_VMGEXIT_GET_AP_JUMP_TABLE 1
> #define SVM_VMGEXIT_PSC 0x80000010
> +#define SVM_VMGEXIT_GUEST_REQUEST 0x80000011
> #define SVM_VMGEXIT_AP_CREATION 0x80000013
> #define SVM_VMGEXIT_AP_CREATE_ON_INIT 0
> #define SVM_VMGEXIT_AP_CREATE 1
> @@ -222,6 +223,7 @@
> { SVM_VMGEXIT_AP_JUMP_TABLE, "vmgexit_ap_jump_table" }, \
> { SVM_VMGEXIT_PSC, "vmgexit_page_state_change" }, \
> { SVM_VMGEXIT_AP_CREATION, "vmgexit_ap_creation" }, \
> + { SVM_VMGEXIT_GUEST_REQUEST, "vmgexit_guest_request" }, \
> { SVM_EXIT_ERR, "invalid_guest_state" }
>
>
> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> index 8f7ef35a25ef..8aae1166f52e 100644
> --- a/arch/x86/kernel/sev.c
> +++ b/arch/x86/kernel/sev.c
> @@ -9,6 +9,7 @@
>
> #define pr_fmt(fmt) "SEV-ES: " fmt
>
> +#include <linux/platform_device.h>
> #include <linux/sched/debug.h> /* For show_regs() */
> #include <linux/percpu-defs.h>
> #include <linux/mem_encrypt.h>
> @@ -16,10 +17,13 @@
> #include <linux/printk.h>
> #include <linux/mm_types.h>
> #include <linux/set_memory.h>
> +#include <linux/sev-guest.h>
> #include <linux/memblock.h>
> #include <linux/kernel.h>
> +#include <linux/efi.h>
> #include <linux/mm.h>
> #include <linux/cpumask.h>
> +#include <linux/io.h>
>
> #include <asm/cpu_entry_area.h>
> #include <asm/stacktrace.h>
> @@ -33,6 +37,7 @@
> #include <asm/smp.h>
> #include <asm/cpu.h>
> #include <asm/apic.h>
> +#include <asm/setup.h> /* For struct boot_params */
>
> #include "sev-internal.h"
>
> @@ -47,6 +52,8 @@ static struct ghcb boot_ghcb_page __bss_decrypted __aligned(PAGE_SIZE);
> */
> static struct ghcb __initdata *boot_ghcb;
>
> +static unsigned long snp_secrets_phys;
> +
> /* #VC handler runtime per-CPU data */
> struct sev_es_runtime_data {
> struct ghcb ghcb_page;
> @@ -105,6 +112,10 @@ struct ghcb_state {
> struct ghcb *ghcb;
> };
>
> +#ifdef CONFIG_EFI
> +extern unsigned long cc_blob_phys;
> +#endif
> +
> static DEFINE_PER_CPU(struct sev_es_runtime_data*, runtime_data);
> DEFINE_STATIC_KEY_FALSE(sev_es_enable_key);
>
> @@ -1909,3 +1920,168 @@ bool __init handle_vc_boot_ghcb(struct pt_regs *regs)
> while (true)
> halt();
> }
> +
> +static struct resource guest_req_res[0];
> +static struct platform_device guest_req_device = {
> + .name = "snp-guest",
> + .id = -1,
> + .resource = guest_req_res,
> + .num_resources = 1,
> +};
> +
> +static struct snp_secrets_page_layout *snp_map_secrets_page(void)
> +{
> + u16 __iomem *secrets;
> +
> + if (!snp_secrets_phys || !sev_feature_enabled(SEV_SNP))
> + return NULL;
> +
> + secrets = ioremap_encrypted(snp_secrets_phys, PAGE_SIZE);
> + if (!secrets)
> + return NULL;
> +
> + return (struct snp_secrets_page_layout *)secrets;
> +}
> +
> +u64 snp_msg_seqno(void)
> +{
> + struct snp_secrets_page_layout *layout;
> + u64 count;
> +
> + layout = snp_map_secrets_page();
> + if (layout == NULL)
> + return 0;
> +
> + /* Read the current message sequence counter from secrets pages */
> + count = readl(&layout->os_area.msg_seqno_0);

Why is this seqno_0 - is that because it's the count of talking to the
PSP?

> + iounmap(layout);
> +
> + /*
> + * The message sequence counter for the SNP guest request is a 64-bit value
> + * but the version 2 of GHCB specification defines the 32-bit storage for the
> + * it.
> + */
> + if ((count + 1) >= INT_MAX)
> + return 0;

Is that UINT_MAX?

> +
> + return count + 1;
> +}
> +EXPORT_SYMBOL_GPL(snp_msg_seqno);
> +
> +static void snp_gen_msg_seqno(void)
> +{
> + struct snp_secrets_page_layout *layout;
> + u64 count;
> +
> + layout = snp_map_secrets_page();
> + if (layout == NULL)
> + return;
> +
> + /* Increment the sequence counter by 2 and save in secrets page. */
> + count = readl(&layout->os_area.msg_seqno_0);
> + count += 2;

Why 2 not 1 ?

> + writel(count, &layout->os_area.msg_seqno_0);
> + iounmap(layout);
> +}
> +
> +static int get_snp_secrets_resource(struct resource *res)
> +{
> + struct setup_header *hdr = &boot_params.hdr;
> + struct cc_blob_sev_info *info;
> + unsigned long paddr;
> + int ret = -ENODEV;
> +
> + /*
> + * The secret page contains the VM encryption key used for encrypting the
> + * messages between the guest and the PSP. The secrets page location is
> + * available either through the setup_data or EFI configuration table.
> + */
> + if (hdr->cc_blob_address) {
> + paddr = hdr->cc_blob_address;

Can you trust the paddr the host has given you or do you need to do some
form of validation?

Dave
> + } else if (efi_enabled(EFI_CONFIG_TABLES)) {
> +#ifdef CONFIG_EFI
> + paddr = cc_blob_phys;
> +#else
> + return -ENODEV;
> +#endif
> + } else {
> + return -ENODEV;
> + }
> +
> + info = memremap(paddr, sizeof(*info), MEMREMAP_WB);
> + if (!info)
> + return -ENOMEM;
> +
> + /* Verify the header that its a valid SEV_SNP CC header */
> + if ((info->magic == CC_BLOB_SEV_HDR_MAGIC) &&
> + info->secrets_phys &&
> + (info->secrets_len == PAGE_SIZE)) {
> + res->start = info->secrets_phys;
> + res->end = info->secrets_phys + info->secrets_len;
> + res->flags = IORESOURCE_MEM;
> + snp_secrets_phys = info->secrets_phys;
> + ret = 0;
> + }
> +
> + memunmap(info);
> + return ret;
> +}
> +
> +static int __init add_snp_guest_request(void)
> +{
> + if (!sev_feature_enabled(SEV_SNP))
> + return -ENODEV;
> +
> + if (get_snp_secrets_resource(&guest_req_res[0]))
> + return -ENODEV;
> +
> + platform_device_register(&guest_req_device);
> + dev_info(&guest_req_device.dev, "registered [secret 0x%llx - 0x%llx]\n",
> + guest_req_res[0].start, guest_req_res[0].end);
> +
> + return 0;
> +}
> +device_initcall(add_snp_guest_request);
> +
> +unsigned long snp_issue_guest_request(int type, struct snp_guest_request_data *input)
> +{
> + struct ghcb_state state;
> + struct ghcb *ghcb;
> + unsigned long id;
> + int ret;
> +
> + if (!sev_feature_enabled(SEV_SNP))
> + return -ENODEV;
> +
> + if (type == GUEST_REQUEST)
> + id = SVM_VMGEXIT_GUEST_REQUEST;
> + else
> + return -EINVAL;
> +
> + ghcb = sev_es_get_ghcb(&state);
> + if (!ghcb)
> + return -ENODEV;
> +
> + vc_ghcb_invalidate(ghcb);
> + ghcb_set_rax(ghcb, input->data_gpa);
> + ghcb_set_rbx(ghcb, input->data_npages);
> +
> + ret = sev_es_ghcb_hv_call(ghcb, NULL, id, input->req_gpa, input->resp_gpa);
> + if (ret)
> + goto e_put;
> +
> + if (ghcb->save.sw_exit_info_2) {
> + ret = ghcb->save.sw_exit_info_2;
> + goto e_put;
> + }
> +
> + /* Command was successful, increment the message sequence counter. */
> + snp_gen_msg_seqno();
> +
> +e_put:
> + sev_es_put_ghcb(&state);
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(snp_issue_guest_request);
> diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
> index 8a26e705cb06..2cca9ee6e1d4 100644
> --- a/arch/x86/platform/efi/efi.c
> +++ b/arch/x86/platform/efi/efi.c
> @@ -57,6 +57,7 @@ static unsigned long efi_systab_phys __initdata;
> static unsigned long prop_phys = EFI_INVALID_TABLE_ADDR;
> static unsigned long uga_phys = EFI_INVALID_TABLE_ADDR;
> static unsigned long efi_runtime, efi_nr_tables;
> +unsigned long cc_blob_phys;
>
> unsigned long efi_fw_vendor, efi_config_table;
>
> @@ -66,6 +67,7 @@ static const efi_config_table_type_t arch_tables[] __initconst = {
> #ifdef CONFIG_X86_UV
> {UV_SYSTEM_TABLE_GUID, &uv_systab_phys, "UVsystab" },
> #endif
> + {EFI_CC_BLOB_GUID, &cc_blob_phys, "CC blob" },
> {},
> };
>
> diff --git a/include/linux/efi.h b/include/linux/efi.h
> index 6b5d36babfcc..75aeb2a56888 100644
> --- a/include/linux/efi.h
> +++ b/include/linux/efi.h
> @@ -344,6 +344,7 @@ void efi_native_runtime_setup(void);
> #define EFI_CERT_SHA256_GUID EFI_GUID(0xc1c41626, 0x504c, 0x4092, 0xac, 0xa9, 0x41, 0xf9, 0x36, 0x93, 0x43, 0x28)
> #define EFI_CERT_X509_GUID EFI_GUID(0xa5c059a1, 0x94e4, 0x4aa7, 0x87, 0xb5, 0xab, 0x15, 0x5c, 0x2b, 0xf0, 0x72)
> #define EFI_CERT_X509_SHA256_GUID EFI_GUID(0x3bd2a492, 0x96c0, 0x4079, 0xb4, 0x20, 0xfc, 0xf9, 0x8e, 0xf1, 0x03, 0xed)
> +#define EFI_CC_BLOB_GUID EFI_GUID(0x067b1f5f, 0xcf26, 0x44c5, 0x85, 0x54, 0x93, 0xd7, 0x77, 0x91, 0x2d, 0x42)
>
> /*
> * This GUID is used to pass to the kernel proper the struct screen_info
> diff --git a/include/linux/sev-guest.h b/include/linux/sev-guest.h
> new file mode 100644
> index 000000000000..51277448a108
> --- /dev/null
> +++ b/include/linux/sev-guest.h
> @@ -0,0 +1,76 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * AMD Secure Encrypted Virtualization (SEV) guest driver interface
> + *
> + * Copyright (C) 2021 Advanced Micro Devices, Inc.
> + *
> + * Author: Brijesh Singh <brijesh.singh@amd.com>
> + *
> + */
> +
> +#ifndef __LINUX_SEV_GUEST_H_
> +#define __LINUX_SEV_GUEST_H_
> +
> +#include <linux/types.h>
> +
> +enum vmgexit_type {
> + GUEST_REQUEST,
> +
> + GUEST_REQUEST_MAX
> +};
> +
> +/*
> + * The secrets page contains 96-bytes of reserved field that can be used by
> + * the guest OS. The guest OS uses the area to save the message sequence
> + * number for each VMPL level.
> + *
> + * See the GHCB spec section Secret page layout for the format for this area.
> + */
> +struct secrets_os_area {
> + u32 msg_seqno_0;
> + u32 msg_seqno_1;
> + u32 msg_seqno_2;
> + u32 msg_seqno_3;
> + u64 ap_jump_table_pa;
> + u8 rsvd[40];
> + u8 guest_usage[32];
> +} __packed;
> +
> +#define VMPCK_KEY_LEN 32
> +
> +/* See the SNP spec secrets page layout section for the structure */
> +struct snp_secrets_page_layout {
> + u32 version;
> + u32 imiEn : 1,
> + rsvd1 : 31;
> + u32 fms;
> + u32 rsvd2;
> + u8 gosvw[16];
> + u8 vmpck0[VMPCK_KEY_LEN];
> + u8 vmpck1[VMPCK_KEY_LEN];
> + u8 vmpck2[VMPCK_KEY_LEN];
> + u8 vmpck3[VMPCK_KEY_LEN];
> + struct secrets_os_area os_area;
> + u8 rsvd3[3840];
> +} __packed;
> +
> +struct snp_guest_request_data {
> + unsigned long req_gpa;
> + unsigned long resp_gpa;
> + unsigned long data_gpa;
> + unsigned int data_npages;
> +};
> +
> +#ifdef CONFIG_AMD_MEM_ENCRYPT
> +unsigned long snp_issue_guest_request(int vmgexit_type, struct snp_guest_request_data *input);
> +u64 snp_msg_seqno(void);
> +#else
> +
> +static inline unsigned long snp_issue_guest_request(int type,
> + struct snp_guest_request_data *input)
> +{
> + return -ENODEV;
> +}
> +static inline u64 snp_msg_seqno(void) { return 0; }
> +#endif /* CONFIG_AMD_MEM_ENCRYPT */
> +#endif /* __LINUX_SEV_GUEST_H__ */
> --
> 2.17.1
>
>
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK