linux/arch/x86/boot/compressed/sev.c

// SPDX-License-Identifier: GPL-2.0
/*
 * AMD Encrypted Register State Support
 *
 * Author: Joerg Roedel <jroedel@suse.de>
 */

/*
 * misc.h needs to be first because it knows how to include the other kernel
 * headers in the pre-decompression code in a way that does not break
 * compilation.
 */
#include "misc.h"

#include <asm/bootparam.h>
#include <asm/pgtable_types.h>
#include <asm/sev.h>
#include <asm/trapnr.h>
#include <asm/trap_pf.h>
#include <asm/msr-index.h>
#include <asm/fpu/xcr.h>
#include <asm/ptrace.h>
#include <asm/svm.h>
#include <asm/cpuid/api.h>

#include "error.h"
#include "sev.h"

static struct ghcb boot_ghcb_page __aligned(PAGE_SIZE);
struct ghcb *boot_ghcb;

#undef __init
#define __init

#undef __head
#define __head

#define __BOOT_COMPRESSED

extern struct svsm_ca *boot_svsm_caa;
extern u64 boot_svsm_caa_pa;

struct svsm_ca *svsm_get_caa(void)
{
	return boot_svsm_caa;
}

u64 svsm_get_caa_pa(void)
{
	return boot_svsm_caa_pa;
}

int svsm_perform_call_protocol(struct svsm_call *call);

u8 snp_vmpl;

/* Include code for early handlers */
#include "../../boot/startup/sev-shared.c"

int svsm_perform_call_protocol(struct svsm_call *call)
{
	struct ghcb *ghcb;
	int ret;

	if (boot_ghcb)
		ghcb = boot_ghcb;
	else
		ghcb = NULL;

	do {
		ret = ghcb ? svsm_perform_ghcb_protocol(ghcb, call)
			   : svsm_perform_msr_protocol(call);
	} while (ret == -EAGAIN);

	return ret;
}

static bool sev_snp_enabled(void)
{
	return sev_status & MSR_AMD64_SEV_SNP_ENABLED;
}

static void __page_state_change(unsigned long paddr, enum psc_op op)
{
	u64 val, msr;

	/*
	 * If private -> shared then invalidate the page before requesting the
	 * state change in the RMP table.
	 */
	if (op == SNP_PAGE_STATE_SHARED)
		pvalidate_4k_page(paddr, paddr, false);

	/* Save the current GHCB MSR value */
	msr = sev_es_rd_ghcb_msr();

	/* Issue VMGEXIT to change the page state in RMP table. */
	sev_es_wr_ghcb_msr(GHCB_MSR_PSC_REQ_GFN(paddr >> PAGE_SHIFT, op));
	VMGEXIT();

	/* Read the response of the VMGEXIT. */
	val = sev_es_rd_ghcb_msr();
	if ((GHCB_RESP_CODE(val) != GHCB_MSR_PSC_RESP) || GHCB_MSR_PSC_RESP_VAL(val))
		sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_PSC);

	/* Restore the GHCB MSR value */
	sev_es_wr_ghcb_msr(msr);

	/*
	 * Now that page state is changed in the RMP table, validate it so that it is
	 * consistent with the RMP entry.
	 */
	if (op == SNP_PAGE_STATE_PRIVATE)
		pvalidate_4k_page(paddr, paddr, true);
}

void snp_set_page_private(unsigned long paddr)
{
	if (!sev_snp_enabled())
		return;

	__page_state_change(paddr, SNP_PAGE_STATE_PRIVATE);
}

void snp_set_page_shared(unsigned long paddr)
{
	if (!sev_snp_enabled())
		return;

	__page_state_change(paddr, SNP_PAGE_STATE_SHARED);
}

bool early_setup_ghcb(void)
{
	if (set_page_decrypted((unsigned long)&boot_ghcb_page))
		return false;

	/* Page is now mapped decrypted, clear it */
	memset(&boot_ghcb_page, 0, sizeof(boot_ghcb_page));

	boot_ghcb = &boot_ghcb_page;

	/* Initialize lookup tables for the instruction decoder */
	sev_insn_decode_init();

	/* SNP guest requires the GHCB GPA must be registered */
	if (sev_snp_enabled())
		snp_register_ghcb_early(__pa(&boot_ghcb_page));

	return true;
}

void snp_accept_memory(phys_addr_t start, phys_addr_t end)
{
	for (phys_addr_t pa = start; pa < end; pa += PAGE_SIZE)
		__page_state_change(pa, SNP_PAGE_STATE_PRIVATE);
}

void sev_es_shutdown_ghcb(void)
{
	if (!boot_ghcb)
		return;

	if (!sev_es_check_cpu_features())
		error("SEV-ES CPU Features missing.");

	/*
	 * This denotes whether to use the GHCB MSR protocol or the GHCB
	 * shared page to perform a GHCB request. Since the GHCB page is
	 * being changed to encrypted, it can't be used to perform GHCB
	 * requests. Clear the boot_ghcb variable so that the GHCB MSR
	 * protocol is used to change the GHCB page over to an encrypted
	 * page.
	 */
	boot_ghcb = NULL;

	/*
	 * GHCB Page must be flushed from the cache and mapped encrypted again.
	 * Otherwise the running kernel will see strange cache effects when
	 * trying to use that page.
	 */
	if (set_page_encrypted((unsigned long)&boot_ghcb_page))
		error("Can't map GHCB page encrypted");

	/*
	 * GHCB page is mapped encrypted again and flushed from the cache.
	 * Mark it non-present now to catch bugs when #VC exceptions trigger
	 * after this point.
	 */
	if (set_page_non_present((unsigned long)&boot_ghcb_page))
		error("Can't unmap GHCB page");
}

static void __noreturn sev_es_ghcb_terminate(struct ghcb *ghcb, unsigned int set,
					     unsigned int reason, u64 exit_info_2)
{
	u64 exit_info_1 = SVM_VMGEXIT_TERM_REASON(set, reason);

	vc_ghcb_invalidate(ghcb);
	ghcb_set_sw_exit_code(ghcb, SVM_VMGEXIT_TERM_REQUEST);
	ghcb_set_sw_exit_info_1(ghcb, exit_info_1);
	ghcb_set_sw_exit_info_2(ghcb, exit_info_2);

	sev_es_wr_ghcb_msr(__pa(ghcb));
	VMGEXIT();

	while (true)
		asm volatile("hlt\n" : : : "memory");
}

bool sev_es_check_ghcb_fault(unsigned long address)
{
	/* Check whether the fault was on the GHCB page */
	return ((address & PAGE_MASK) == (unsigned long)&boot_ghcb_page);
}

/*
 * SNP_FEATURES_IMPL_REQ is the mask of SNP features that will need
 * guest side implementation for proper functioning of the guest. If any
 * of these features are enabled in the hypervisor but are lacking guest
 * side implementation, the behavior of the guest will be undefined. The
 * guest could fail in non-obvious way making it difficult to debug.
 *
 * As the behavior of reserved feature bits is unknown to be on the
 * safe side add them to the required features mask.
 */
#define SNP_FEATURES_IMPL_REQ	(MSR_AMD64_SNP_VTOM |			\
				 MSR_AMD64_SNP_REFLECT_VC |		\
				 MSR_AMD64_SNP_RESTRICTED_INJ |		\
				 MSR_AMD64_SNP_ALT_INJ |		\
				 MSR_AMD64_SNP_DEBUG_SWAP |		\
				 MSR_AMD64_SNP_VMPL_SSS |		\
				 MSR_AMD64_SNP_SECURE_TSC |		\
				 MSR_AMD64_SNP_VMGEXIT_PARAM |		\
				 MSR_AMD64_SNP_VMSA_REG_PROT |		\
				 MSR_AMD64_SNP_RESERVED_BIT13 |		\
				 MSR_AMD64_SNP_RESERVED_BIT15 |		\
				 MSR_AMD64_SNP_RESERVED_MASK)

/*
 * SNP_FEATURES_PRESENT is the mask of SNP features that are implemented
 * by the guest kernel. As and when a new feature is implemented in the
 * guest kernel, a corresponding bit should be added to the mask.
 */
#define SNP_FEATURES_PRESENT	(MSR_AMD64_SNP_DEBUG_SWAP |	\
				 MSR_AMD64_SNP_SECURE_TSC)

u64 snp_get_unsupported_features(u64 status)
{
	if (!(status & MSR_AMD64_SEV_SNP_ENABLED))
		return 0;

	return status & SNP_FEATURES_IMPL_REQ & ~SNP_FEATURES_PRESENT;
}

void snp_check_features(void)
{
	u64 unsupported;

	/*
	 * Terminate the boot if hypervisor has enabled any feature lacking
	 * guest side implementation. Pass on the unsupported features mask through
	 * EXIT_INFO_2 of the GHCB protocol so that those features can be reported
	 * as part of the guest boot failure.
	 */
	unsupported = snp_get_unsupported_features(sev_status);
	if (unsupported) {
		if (ghcb_version < 2 || (!boot_ghcb && !early_setup_ghcb()))
			sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SNP_UNSUPPORTED);

		sev_es_ghcb_terminate(boot_ghcb, SEV_TERM_SET_GEN,
				      GHCB_SNP_UNSUPPORTED, unsupported);
	}
}

/* Search for Confidential Computing blob in the EFI config table. */
static struct cc_blob_sev_info *find_cc_blob_efi(struct boot_params *bp)
{
	unsigned long cfg_table_pa;
	unsigned int cfg_table_len;
	int ret;

	ret = efi_get_conf_table(bp, &cfg_table_pa, &cfg_table_len);
	if (ret)
		return NULL;

	return (struct cc_blob_sev_info *)efi_find_vendor_table(bp, cfg_table_pa,
								cfg_table_len,
								EFI_CC_BLOB_GUID);
}

/*
 * Initial set up of SNP relies on information provided by the
 * Confidential Computing blob, which can be passed to the boot kernel
 * by firmware/bootloader in the following ways:
 *
 * - via an entry in the EFI config table
 * - via a setup_data structure, as defined by the Linux Boot Protocol
 *
 * Scan for the blob in that order.
 */
static struct cc_blob_sev_info *find_cc_blob(struct boot_params *bp)
{
	struct cc_blob_sev_info *cc_info;

	cc_info = find_cc_blob_efi(bp);
	if (cc_info)
		goto found_cc_info;

	cc_info = find_cc_blob_setup_data(bp);
	if (!cc_info)
		return NULL;

found_cc_info:
	if (cc_info->magic != CC_BLOB_SEV_HDR_MAGIC)
		sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SNP_UNSUPPORTED);

	return cc_info;
}

/*
 * Indicate SNP based on presence of SNP-specific CC blob. Subsequent checks
 * will verify the SNP CPUID/MSR bits.
 */
static bool early_snp_init(struct boot_params *bp)
{
	struct cc_blob_sev_info *cc_info;

	if (!bp)
		return false;

	cc_info = find_cc_blob(bp);
	if (!cc_info)
		return false;

	/*
	 * If a SNP-specific Confidential Computing blob is present, then
	 * firmware/bootloader have indicated SNP support. Verifying this
	 * involves CPUID checks which will be more reliable if the SNP
	 * CPUID table is used. See comments over snp_setup_cpuid_table() for
	 * more details.
	 */
	setup_cpuid_table(cc_info);

	/*
	 * Record the SVSM Calling Area (CA) address if the guest is not
	 * running at VMPL0. The CA will be used to communicate with the
	 * SVSM and request its services.
	 */
	svsm_setup_ca(cc_info);

	/*
	 * Pass run-time kernel a pointer to CC info via boot_params so EFI
	 * config table doesn't need to be searched again during early startup
	 * phase.
	 */
	bp->cc_blob_address = (u32)(unsigned long)cc_info;

	return true;
}

/*
 * sev_check_cpu_support - Check for SEV support in the CPU capabilities
 *
 * Returns < 0 if SEV is not supported, otherwise the position of the
 * encryption bit in the page table descriptors.
 */
static int sev_check_cpu_support(void)
{
	unsigned int eax, ebx, ecx, edx;

	/* Check for the SME/SEV support leaf */
	eax = 0x80000000;
	ecx = 0;
	native_cpuid(&eax, &ebx, &ecx, &edx);
	if (eax < 0x8000001f)
		return -ENODEV;

	/*
	 * Check for the SME/SEV feature:
	 *   CPUID Fn8000_001F[EAX]
	 *   - Bit 0 - Secure Memory Encryption support
	 *   - Bit 1 - Secure Encrypted Virtualization support
	 *   CPUID Fn8000_001F[EBX]
	 *   - Bits 5:0 - Pagetable bit position used to indicate encryption
	 */
	eax = 0x8000001f;
	ecx = 0;
	native_cpuid(&eax, &ebx, &ecx, &edx);
	/* Check whether SEV is supported */
	if (!(eax & BIT(1)))
		return -ENODEV;

	return ebx & 0x3f;
}

void sev_enable(struct boot_params *bp)
{
	struct msr m;
	int bitpos;
	bool snp;

	/*
	 * bp->cc_blob_address should only be set by boot/compressed kernel.
	 * Initialize it to 0 to ensure that uninitialized values from
	 * buggy bootloaders aren't propagated.
	 */
	if (bp)
		bp->cc_blob_address = 0;

	/*
	 * Do an initial SEV capability check before early_snp_init() which
	 * loads the CPUID page and the same checks afterwards are done
	 * without the hypervisor and are trustworthy.
	 *
	 * If the HV fakes SEV support, the guest will crash'n'burn
	 * which is good enough.
	 */

	if (sev_check_cpu_support() < 0)
		return;

	/*
	 * Setup/preliminary detection of SNP. This will be sanity-checked
	 * against CPUID/MSR values later.
	 */
	snp = early_snp_init(bp);

	/* Now repeat the checks with the SNP CPUID table. */

	bitpos = sev_check_cpu_support();
	if (bitpos < 0) {
		if (snp)
			error("SEV-SNP support indicated by CC blob, but not CPUID.");
		return;
	}

	/* Set the SME mask if this is an SEV guest. */
	boot_rdmsr(MSR_AMD64_SEV, &m);
	sev_status = m.q;
	if (!(sev_status & MSR_AMD64_SEV_ENABLED))
		return;

	/* Negotiate the GHCB protocol version. */
	if (sev_status & MSR_AMD64_SEV_ES_ENABLED) {
		if (!sev_es_negotiate_protocol())
			sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SEV_ES_PROT_UNSUPPORTED);
	}

	/*
	 * SNP is supported in v2 of the GHCB spec which mandates support for HV
	 * features.
	 */
	if (sev_status & MSR_AMD64_SEV_SNP_ENABLED) {
		u64 hv_features;
		int ret;

		hv_features = get_hv_features();
		if (!(hv_features & GHCB_HV_FT_SNP))
			sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SNP_UNSUPPORTED);

		/*
		 * Enforce running at VMPL0 or with an SVSM.
		 *
		 * Use RMPADJUST (see the rmpadjust() function for a description of
		 * what the instruction does) to update the VMPL1 permissions of a
		 * page. If the guest is running at VMPL0, this will succeed. If the
		 * guest is running at any other VMPL, this will fail. Linux SNP guests
		 * only ever run at a single VMPL level so permission mask changes of a
		 * lesser-privileged VMPL are a don't-care.
		 */
		ret = rmpadjust((unsigned long)&boot_ghcb_page, RMP_PG_SIZE_4K, 1);

		/*
		 * Running at VMPL0 is not required if an SVSM is present and the hypervisor
		 * supports the required SVSM GHCB events.
		 */
		if (ret &&
		    !(snp_vmpl && (hv_features & GHCB_HV_FT_SNP_MULTI_VMPL)))
			sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_NOT_VMPL0);
	}

	if (snp && !(sev_status & MSR_AMD64_SEV_SNP_ENABLED))
		error("SEV-SNP supported indicated by CC blob, but not SEV status MSR.");

	sme_me_mask = BIT_ULL(bitpos);
}

/*
 * sev_get_status - Retrieve the SEV status mask
 *
 * Returns 0 if the CPU is not SEV capable, otherwise the value of the
 * AMD64_SEV MSR.
 */
u64 sev_get_status(void)
{
	struct msr m;

	if (sev_check_cpu_support() < 0)
		return 0;

	boot_rdmsr(MSR_AMD64_SEV, &m);
	return m.q;
}

void sev_prep_identity_maps(unsigned long top_level_pgt)
{
	/*
	 * The Confidential Computing blob is used very early in uncompressed
	 * kernel to find the in-memory CPUID table to handle CPUID
	 * instructions. Make sure an identity-mapping exists so it can be
	 * accessed after switchover.
	 */
	if (sev_snp_enabled()) {
		unsigned long cc_info_pa = boot_params_ptr->cc_blob_address;
		struct cc_blob_sev_info *cc_info;

		kernel_add_identity_map(cc_info_pa, cc_info_pa + sizeof(*cc_info));

		cc_info = (struct cc_blob_sev_info *)cc_info_pa;
		kernel_add_identity_map(cc_info->cpuid_phys, cc_info->cpuid_phys + cc_info->cpuid_len);
	}

	sev_verify_cbit(top_level_pgt);
}

bool early_is_sevsnp_guest(void)
{
	static bool sevsnp;

	if (sevsnp)
		return true;

	if (!(sev_get_status() & MSR_AMD64_SEV_SNP_ENABLED))
		return false;

	sevsnp = true;

	if (!snp_vmpl) {
		unsigned int eax, ebx, ecx, edx;

		/*
		 * CPUID Fn8000_001F_EAX[28] - SVSM support
		 */
		eax = 0x8000001f;
		ecx = 0;
		native_cpuid(&eax, &ebx, &ecx, &edx);
		if (eax & BIT(28)) {
			struct msr m;

			/* Obtain the address of the calling area to use */
			boot_rdmsr(MSR_SVSM_CAA, &m);
			boot_svsm_caa = (void *)m.q;
			boot_svsm_caa_pa = m.q;

			/*
			 * The real VMPL level cannot be discovered, but the
			 * memory acceptance routines make no use of that so
			 * any non-zero value suffices here.
			 */
			snp_vmpl = U8_MAX;
		}
	}
	return true;
}