Re: [PATCH v3 03/14] x86/sev: Check for the presence of an SVSM in the SNP Secrets page
From: Tom Lendacky
Date: Thu Apr 18 2024 - 17:17:52 EST
On 4/17/24 15:40, Borislav Petkov wrote:
On Mon, Mar 25, 2024 at 05:26:22PM -0500, Tom Lendacky wrote:
During early boot phases, check for the presence of an SVSM when running
as an SEV-SNP guest.
An SVSM is present if the 64-bit value at offset 0x148 into the secrets
page is non-zero. If an SVSM is present, save the SVSM Calling Area
address (CAA), located at offset 0x150 into the secrets page, and set
the VMPL level of the guest, which should be non-zero, to indicate the
presence of an SVSM.
Where are we pointing to the SVSM spec?
This is in the 0th message
https://www.amd.com/content/dam/amd/en/documents/epyc-technical-docs/specifications/58019.pdf
but pls add it to our documentation here:
Documentation/arch/x86/amd-memory-encryption.rst
Do you want it added as a in this patch or in a documentation patch at the
end of the series?
Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
---
arch/x86/boot/compressed/sev.c | 35 ++++++++---------
arch/x86/include/asm/sev-common.h | 4 ++
arch/x86/include/asm/sev.h | 25 +++++++++++-
arch/x86/kernel/sev-shared.c | 64 +++++++++++++++++++++++++++++++
arch/x86/kernel/sev.c | 16 ++++++++
5 files changed, 125 insertions(+), 19 deletions(-)
diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
index 49dc9661176d..fe61ff630c7e 100644
--- a/arch/x86/boot/compressed/sev.c
+++ b/arch/x86/boot/compressed/sev.c
@@ -12,6 +12,7 @@
*/
#include "misc.h"
+#include <linux/mm.h>
#include <asm/bootparam.h>
#include <asm/pgtable_types.h>
#include <asm/sev.h>
@@ -29,6 +30,15 @@
static struct ghcb boot_ghcb_page __aligned(PAGE_SIZE);
struct ghcb *boot_ghcb;
+/*
+ * SVSM related information:
+ * When running under an SVSM, the VMPL that Linux is executing at must be
+ * non-zero. The VMPL is therefore used to indicate the presence of an SVSM.
+ */
+static u8 vmpl __section(".data");
+static u64 boot_svsm_caa_pa __section(".data");
+static struct svsm_ca *boot_svsm_caa __section(".data");
Explain what those last 2 are in comments above it pls.
Will do.
/*
* SNP_FEATURES_IMPL_REQ is the mask of SNP features that will need
* guest side implementation for proper functioning of the guest. If any
@@ -480,6 +472,13 @@ static bool early_snp_init(struct boot_params *bp)
*/
setup_cpuid_table(cc_info);
+ /*
+ * Record the SVSM Calling Area address (CAA) if the guest is not
Calling Area (CA) address
+ * running at VMPL0. The CA will be used to communicate with the
and then you can use "CA" here.
Will do.
+ * SVSM to perform the SVSM services.
+ */
+ setup_svsm_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
diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
index b463fcbd4b90..68a8cdf6fd6a 100644
--- a/arch/x86/include/asm/sev-common.h
+++ b/arch/x86/include/asm/sev-common.h
@@ -159,6 +159,10 @@ struct snp_psc_desc {
#define GHCB_TERM_NOT_VMPL0 3 /* SNP guest is not running at VMPL-0 */
#define GHCB_TERM_CPUID 4 /* CPUID-validation failure */
#define GHCB_TERM_CPUID_HV 5 /* CPUID failure during hypervisor fallback */
+#define GHCB_TERM_SECRETS_PAGE 6 /* Secrets page failure */
+#define GHCB_TERM_NO_SVSM 7 /* SVSM is not advertised in the secrets page */
+#define GHCB_TERM_SVSM_VMPL0 8 /* SVSM is present but has set VMPL to 0 */
+#define GHCB_TERM_SVSM_CAA 9 /* SVSM is present but the CA is not page aligned */
"CAA" in the comment I guess. :)
Will do.
+/*
+ * Maintain the GPA of the SVSM Calling Area (CA) in order to utilize the SVSM
+ * services needed when not running in VMPL0.
+ */
+static void __head setup_svsm_ca(const struct cc_blob_sev_info *cc_info)
+{
+ struct snp_secrets_page_layout *secrets_page;
Why was that thing ever called "_layout" and not simply
snp_secrets_page?
Fix it?
Sure, I can change that as a pre-patch to the series.
+ u64 caa;
+
+ BUILD_BUG_ON(sizeof(*secrets_page) != PAGE_SIZE);
Put it in the header under the struct definition I guess.
It can't stand on it's own in the header file. I'd have to put it in a
#define or an inline function and then use that in some code. So it's
probably best to keep it here.
+ /*
+ * Use __pa() since this routine is running identity mapped when
+ * called, both by the decompressor code and the early kernel code.
+ */
+ if (running_at_vmpl0((void *)__pa(&boot_ghcb_page)))
+ return;
+
+ /*
+ * Not running at VMPL0, ensure everything has been properly supplied
+ * for running under an SVSM.
+ */
+ if (!cc_info || !cc_info->secrets_phys || cc_info->secrets_len != PAGE_SIZE)
+ sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_SECRETS_PAGE);
+
+ secrets_page = (struct snp_secrets_page_layout *)cc_info->secrets_phys;
+ if (!secrets_page->svsm_size)
+ sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_NO_SVSM);
+
+ if (!secrets_page->svsm_guest_vmpl)
+ sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_SVSM_VMPL0);
+
+ vmpl = secrets_page->svsm_guest_vmpl;
+
+ caa = secrets_page->svsm_caa;
+ if (!PAGE_ALIGNED(caa))
+ sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_SVSM_CAA);
+
+ /*
+ * The CA is identity mapped when this routine is called, both by the
+ * decompressor code and the early kernel code.
+ */
+ boot_svsm_caa = (struct svsm_ca *)caa;
+ boot_svsm_caa_pa = caa;
+}
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index b59b09c2f284..64799a04feb4 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -135,6 +135,15 @@ struct ghcb_state {
static DEFINE_PER_CPU(struct sev_es_runtime_data*, runtime_data);
static DEFINE_PER_CPU(struct sev_es_save_area *, sev_vmsa);
+/*
+ * SVSM related information:
+ * When running under an SVSM, the VMPL that Linux is executing at must be
+ * non-zero. The VMPL is therefore used to indicate the presence of an SVSM.
+ */
+static u8 vmpl __ro_after_init;
+static struct svsm_ca *boot_svsm_caa __ro_after_init;
+static u64 boot_svsm_caa_pa __ro_after_init;
Uff, duplication.
Let's put them in sev-shared.c pls and avoid that.
Ok, but it will require moving some functions after the inclusion of
sev-shared.c and then (later) adding some advance function declarations.
Thanks,
Tom
Thx.