Commit 30612045 authored by Michael Roth's avatar Michael Roth Committed by Borislav Petkov
Browse files

x86/sev: Use firmware-validated CPUID for SEV-SNP guests 



SEV-SNP guests will be provided the location of special 'secrets' and
'CPUID' pages via the Confidential Computing blob. This blob is
provided to the run-time kernel either through a boot_params field that
was initialized by the boot/compressed kernel, or via a setup_data
structure as defined by the Linux Boot Protocol.

Locate the Confidential Computing blob from these sources and, if found,
use the provided CPUID page/table address to create a copy that the
run-time kernel will use when servicing CPUID instructions via a #VC
handler.

Signed-off-by: default avatarMichael Roth <michael.roth@amd.com>
Signed-off-by: default avatarBrijesh Singh <brijesh.singh@amd.com>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220307213356.2797205-40-brijesh.singh@amd.com
parent b190a043

arch/x86/boot/compressed/sev.c

+0 −37
Original line number Original line Diff line number Diff line
@@ -381,43 +381,6 @@ static struct cc_blob_sev_info *find_cc_blob(struct boot_params *bp) 
	return cc_info;

	return cc_info;

}

}





/*

 * Initialize the kernel's copy of the SNP CPUID table, and set up the

 * pointer that will be used to access it.

 *

 * Maintaining a direct mapping of the SNP CPUID table used by firmware would

 * be possible as an alternative, but the approach is brittle since the

 * mapping needs to be updated in sync with all the changes to virtual memory

 * layout and related mapping facilities throughout the boot process.

 */

static void setup_cpuid_table(const struct cc_blob_sev_info *cc_info)

{

	const struct snp_cpuid_table *cpuid_table_fw, *cpuid_table;

	int i;



	if (!cc_info || !cc_info->cpuid_phys || cc_info->cpuid_len < PAGE_SIZE)

		sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_CPUID);



	cpuid_table_fw = (const struct snp_cpuid_table *)cc_info->cpuid_phys;

	if (!cpuid_table_fw->count || cpuid_table_fw->count > SNP_CPUID_COUNT_MAX)

		sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_CPUID);



	cpuid_table = snp_cpuid_get_table();

	memcpy((void *)cpuid_table, cpuid_table_fw, sizeof(*cpuid_table));



	/* Initialize CPUID ranges for range-checking. */

	for (i = 0; i < cpuid_table->count; i++) {

		const struct snp_cpuid_fn *fn = &cpuid_table->fn[i];



		if (fn->eax_in == 0x0)

			cpuid_std_range_max = fn->eax;

		else if (fn->eax_in == 0x40000000)

			cpuid_hyp_range_max = fn->eax;

		else if (fn->eax_in == 0x80000000)

			cpuid_ext_range_max = fn->eax;

	}

}



/*

/*

 * Indicate SNP based on presence of SNP-specific CC blob. Subsequent checks

 * Indicate SNP based on presence of SNP-specific CC blob. Subsequent checks

 * will verify the SNP CPUID/MSR bits.

 * will verify the SNP CPUID/MSR bits.

arch/x86/kernel/sev-shared.c

+37 −0
Original line number Original line Diff line number Diff line
@@ -964,3 +964,40 @@ static struct cc_blob_sev_info *find_cc_blob_setup_data(struct boot_params *bp) 




	return NULL;

	return NULL;

}

}



/*

 * Initialize the kernel's copy of the SNP CPUID table, and set up the

 * pointer that will be used to access it.

 *

 * Maintaining a direct mapping of the SNP CPUID table used by firmware would

 * be possible as an alternative, but the approach is brittle since the

 * mapping needs to be updated in sync with all the changes to virtual memory

 * layout and related mapping facilities throughout the boot process.

 */

static void __init setup_cpuid_table(const struct cc_blob_sev_info *cc_info)

{

	const struct snp_cpuid_table *cpuid_table_fw, *cpuid_table;

	int i;



	if (!cc_info || !cc_info->cpuid_phys || cc_info->cpuid_len < PAGE_SIZE)

		sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_CPUID);



	cpuid_table_fw = (const struct snp_cpuid_table *)cc_info->cpuid_phys;

	if (!cpuid_table_fw->count || cpuid_table_fw->count > SNP_CPUID_COUNT_MAX)

		sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_CPUID);



	cpuid_table = snp_cpuid_get_table();

	memcpy((void *)cpuid_table, cpuid_table_fw, sizeof(*cpuid_table));



	/* Initialize CPUID ranges for range-checking. */

	for (i = 0; i < cpuid_table->count; i++) {

		const struct snp_cpuid_fn *fn = &cpuid_table->fn[i];



		if (fn->eax_in == 0x0)

			cpuid_std_range_max = fn->eax;

		else if (fn->eax_in == 0x40000000)

			cpuid_hyp_range_max = fn->eax;

		else if (fn->eax_in == 0x80000000)

			cpuid_ext_range_max = fn->eax;

	}

}

arch/x86/kernel/sev.c

+24 −0
Original line number Original line Diff line number Diff line
@@ -34,6 +34,7 @@ 
#include <asm/cpu.h>

#include <asm/cpu.h>

#include <asm/apic.h>

#include <asm/apic.h>

#include <asm/cpuid.h>

#include <asm/cpuid.h>

#include <asm/cmdline.h>





#define DR7_RESET_VALUE        0x400

#define DR7_RESET_VALUE        0x400
@@ -2025,6 +2026,8 @@ bool __init snp_init(struct boot_params *bp) 
	if (!cc_info)

	if (!cc_info)

		return false;

		return false;





	setup_cpuid_table(cc_info);



	/*

	/*

	 * The CC blob will be used later to access the secrets page. Cache

	 * The CC blob will be used later to access the secrets page. Cache

	 * it here like the boot kernel does.

	 * it here like the boot kernel does.
@@ -2038,3 +2041,24 @@ void __init snp_abort(void) 
{

{

	sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SNP_UNSUPPORTED);

	sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SNP_UNSUPPORTED);

}

}



/*

 * It is useful from an auditing/testing perspective to provide an easy way

 * for the guest owner to know that the CPUID table has been initialized as

 * expected, but that initialization happens too early in boot to print any

 * sort of indicator, and there's not really any other good place to do it,

 * so do it here.

 */

static int __init report_cpuid_table(void)

{

	const struct snp_cpuid_table *cpuid_table = snp_cpuid_get_table();



	if (!cpuid_table->count)

		return 0;



	pr_info("Using SNP CPUID table, %d entries present.\n",

		cpuid_table->count);



	return 0;

}

arch_initcall(report_cpuid_table);