[v8,35/40] x86/sev: use firmware-validated CPUID for SEV-SNP guests

Commit Message

Brijesh Singh Dec. 10, 2021, 3:43 p.m. UTC

From: Michael Roth <[e-mail]>

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 bootparams 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 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 <[e-mail]>
Signed-off-by: Brijesh Singh <[e-mail]>
---
 arch/x86/include/asm/sev.h   | 10 ----------
 arch/x86/kernel/sev-shared.c |  2 +-
 arch/x86/kernel/sev.c        | 37 ++++++++++++++++++++++++++++++++++++
 3 files changed, 38 insertions(+), 11 deletions(-)

Comments

Borislav Petkov Jan. 26, 2022, 6:35 p.m. UTC | #1

On Fri, Dec 10, 2021 at 09:43:27AM -0600, Brijesh Singh wrote:
> From: Michael Roth <[e-mail]>
> 
> 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 bootparams field that
						^
						a


> was initialized by the boot/compressed kernel, or via a setup_data
> structure as defined by the Linux Boot Protocol.
> 
> Locate the Confidential Computing from these sources and, if found,
				   ^
				   blob

> 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
					  ^^^^^

Please capitalize all instruction mnemonics in text.

> +/*
> + * 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, and while at it, go ahead and re-verify that nothing strange has
> + * happened between early boot and now.
> + */
> +static int __init snp_cpuid_check_status(void)

That function's redundant now, I believe, since we terminate the guest
if there's something wrong with the CPUID page.

Patch

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 4d32af1348ed..76a208fd451b 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -148,16 +148,6 @@  void snp_set_memory_private(unsigned long vaddr, unsigned int npages);
 void snp_set_wakeup_secondary_cpu(void);
 bool snp_init(struct boot_params *bp);
 void snp_abort(void);
-/*
- * TODO: These are exported only temporarily while boot/compressed/sev.c is
- * the only user. This is to avoid unused function warnings for kernel/sev.c
- * during the build of kernel proper.
- *
- * Once the code is added to consume these in kernel proper these functions
- * can be moved back to being statically-scoped to units that pull in
- * sev-shared.c via #include and these declarations can be dropped.
- */
-void snp_cpuid_info_create(const struct cc_blob_sev_info *cc_info);
 #else
 static inline void sev_es_ist_enter(struct pt_regs *regs) { }
 static inline void sev_es_ist_exit(void) { }
diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
index 72836abcdbe2..7bc7e297f88c 100644
--- a/arch/x86/kernel/sev-shared.c
+++ b/arch/x86/kernel/sev-shared.c
@@ -995,7 +995,7 @@  snp_find_cc_blob_setup_data(struct boot_params *bp)
  * mapping needs to be updated in sync with all the changes to virtual memory
  * layout and related mapping facilities throughout the boot process.
  */
-void __init snp_cpuid_info_create(const struct cc_blob_sev_info *cc_info)
+static void __init snp_cpuid_info_create(const struct cc_blob_sev_info *cc_info)
 {
 	const struct snp_cpuid_info *cpuid_info_fw, *cpuid_info;
 
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 0e5c45eacc77..70e18b98bb68 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -2001,6 +2001,12 @@  bool __init snp_init(struct boot_params *bp)
 	if (!cc_info)
 		return false;
 
+	snp_cpuid_info_create(cc_info);
+
+	/* SEV-SNP CPUID table is set up now. Do some sanity checks. */
+	if (!snp_cpuid_active())
+		sev_es_terminate(1, GHCB_TERM_CPUID);
+
 	/*
 	 * The CC blob will be used later to access the secrets page. Cache
 	 * it here like the boot kernel does.
@@ -2014,3 +2020,34 @@  void __init snp_abort(void)
 {
 	sev_es_terminate(1, 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, and while at it, go ahead and re-verify that nothing strange has
+ * happened between early boot and now.
+ */
+static int __init snp_cpuid_check_status(void)
+{
+	const struct snp_cpuid_info *cpuid_info = snp_cpuid_info_get_ptr();
+
+	if (!cc_platform_has(CC_ATTR_SEV_SNP)) {
+		/* Firmware should not have advertised the feature. */
+		if (snp_cpuid_active())
+			panic("Invalid use of SEV-SNP CPUID table.");
+		return 0;
+	}
+
+	/* CPUID table should always be available when SEV-SNP is enabled. */
+	if (!snp_cpuid_active())
+		sev_es_terminate(1, GHCB_TERM_CPUID);
+
+	pr_info("Using SEV-SNP CPUID table, %d entries present.\n",
+		cpuid_info->count);
+
+	return 0;
+}
+
+arch_initcall(snp_cpuid_check_status);