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

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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: Michael Roth <michael.roth@amd.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220307213356.2797205-40-brijesh.singh@amd.com
This commit is contained in:
Michael Roth 2022-03-07 15:33:49 -06:00 committed by Borislav Petkov
parent b190a043c4
commit 30612045e6
3 changed files with 61 additions and 37 deletions
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37
arch/x86/boot/compressed/sev.c
View File

@ -381,43 +381,6 @@ found_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
* will verify the SNP CPUID/MSR bits.

37
arch/x86/kernel/sev-shared.c
View File

@ -964,3 +964,40 @@ static struct cc_blob_sev_info *find_cc_blob_setup_data(struct boot_params *bp)
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;
}
}

24
arch/x86/kernel/sev.c
View File

@ -34,6 +34,7 @@
#include <asm/cpu.h>
#include <asm/apic.h>
#include <asm/cpuid.h>
#include <asm/cmdline.h>
#define DR7_RESET_VALUE 0x400
@ -2025,6 +2026,8 @@ bool __init snp_init(struct boot_params *bp)
if (!cc_info)
return false;
setup_cpuid_table(cc_info);
/*
* The CC blob will be used later to access the secrets page. Cache
* 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);
}
/*
* 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);