[PATCH] x86/sev: get the AP jump table address from secrets page

[PATCH] x86/sev: get the AP jump table address from secrets page

[Michael Roth]

From: Brijesh Singh <brijesh.singh@amd.com>

The GHCB specification section 2.7 states that when SEV-SNP is enabled,
a hypervisor must provide the AP jump table physical address through
the SNP secrets pages.

Fixes: 0afb6b660a6b ("x86/sev: Use SEV-SNP AP creation to start secondary CPUs")
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 arch/x86/include/asm/sev.h            | 35 ++++++++++++++
 arch/x86/kernel/sev.c                 | 70 ++++++++++++++++++---------
 drivers/virt/coco/sevguest/sevguest.h | 35 --------------
 3 files changed, 81 insertions(+), 59 deletions(-)

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 9c2d33f1cfee..509a23c85fe8 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -99,6 +99,41 @@ struct snp_guest_platform_data {
 	u64 secrets_gpa;
 };
 
+/*
+ * The secrets page contains 96-bytes of reserved field that can be used by
+ * the guest OS. The guest OS uses the area to save the message sequence
+ * number for each VMPCK.
+ *
+ * See the GHCB spec section Secret page layout for the format for this area.
+ */
+struct secrets_os_area {
+	u32 msg_seqno_0;
+	u32 msg_seqno_1;
+	u32 msg_seqno_2;
+	u32 msg_seqno_3;
+	u64 ap_jump_table_pa;
+	u8 rsvd[40];
+	u8 guest_usage[32];
+} __packed;
+
+#define VMPCK_KEY_LEN		32
+
+/* See the SNP spec version 0.9 for secrets page format */
+struct snp_secrets_page_layout {
+	u32 version;
+	u32 imien	: 1,
+	    rsvd1	: 31;
+	u32 fms;
+	u32 rsvd2;
+	u8 gosvw[16];
+	u8 vmpck0[VMPCK_KEY_LEN];
+	u8 vmpck1[VMPCK_KEY_LEN];
+	u8 vmpck2[VMPCK_KEY_LEN];
+	u8 vmpck3[VMPCK_KEY_LEN];
+	struct secrets_os_area os_area;
+	u8 rsvd3[3840];
+} __packed;
+
 #ifdef CONFIG_AMD_MEM_ENCRYPT
 extern struct static_key_false sev_es_enable_key;
 extern void __sev_es_ist_enter(struct pt_regs *regs);
diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index f01f4550e2c6..9cb27490745c 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -558,6 +558,49 @@ void noinstr __sev_es_nmi_complete(void)
 	__sev_put_ghcb(&state);
 }
 
+static u64 get_secrets_page(void)
+{
+	u64 pa_data = boot_params.cc_blob_address;
+	struct cc_blob_sev_info info;
+	void *map;
+
+	/*
+	 * The CC blob contains the address of the secrets page, check if the
+	 * blob is present.
+	 */
+	if (!pa_data)
+		return 0;
+
+	map = early_memremap(pa_data, sizeof(info));
+	memcpy(&info, map, sizeof(info));
+	early_memunmap(map, sizeof(info));
+
+	/* smoke-test the secrets page passed */
+	if (!info.secrets_phys || info.secrets_len != PAGE_SIZE)
+		return 0;
+
+	return info.secrets_phys;
+}
+
+static u64 get_snp_jump_table_addr(void)
+{
+	struct snp_secrets_page_layout *layout;
+	u64 pa = get_secrets_page();
+	u64 addr;
+
+	if (!pa)
+		return 0;
+
+	layout = (__force void *)ioremap_encrypted(pa, PAGE_SIZE);
+	if (!layout)
+		return 0;
+
+	addr = layout->os_area.ap_jump_table_pa;
+	iounmap(layout);
+
+	return addr;
+}
+
 static u64 get_jump_table_addr(void)
 {
 	struct ghcb_state state;
@@ -565,6 +608,9 @@ static u64 get_jump_table_addr(void)
 	struct ghcb *ghcb;
 	u64 ret = 0;
 
+	if (cc_platform_has(CC_ATTR_GUEST_SEV_SNP))
+		return get_snp_jump_table_addr();
+
 	local_irq_save(flags);
 
 	ghcb = __sev_get_ghcb(&state);
@@ -2171,30 +2217,6 @@ static struct platform_device guest_req_device = {
 	.id		= -1,
 };
 
-static u64 get_secrets_page(void)
-{
-	u64 pa_data = boot_params.cc_blob_address;
-	struct cc_blob_sev_info info;
-	void *map;
-
-	/*
-	 * The CC blob contains the address of the secrets page, check if the
-	 * blob is present.
-	 */
-	if (!pa_data)
-		return 0;
-
-	map = early_memremap(pa_data, sizeof(info));
-	memcpy(&info, map, sizeof(info));
-	early_memunmap(map, sizeof(info));
-
-	/* smoke-test the secrets page passed */
-	if (!info.secrets_phys || info.secrets_len != PAGE_SIZE)
-		return 0;
-
-	return info.secrets_phys;
-}
-
 static int __init snp_init_platform_device(void)
 {
 	struct snp_guest_platform_data data;
diff --git a/drivers/virt/coco/sevguest/sevguest.h b/drivers/virt/coco/sevguest/sevguest.h
index d39bdd013765..21bda26fdb95 100644
--- a/drivers/virt/coco/sevguest/sevguest.h
+++ b/drivers/virt/coco/sevguest/sevguest.h
@@ -60,39 +60,4 @@ struct snp_guest_msg {
 	u8 payload[4000];
 } __packed;
 
-/*
- * The secrets page contains 96-bytes of reserved field that can be used by
- * the guest OS. The guest OS uses the area to save the message sequence
- * number for each VMPCK.
- *
- * See the GHCB spec section Secret page layout for the format for this area.
- */
-struct secrets_os_area {
-	u32 msg_seqno_0;
-	u32 msg_seqno_1;
-	u32 msg_seqno_2;
-	u32 msg_seqno_3;
-	u64 ap_jump_table_pa;
-	u8 rsvd[40];
-	u8 guest_usage[32];
-} __packed;
-
-#define VMPCK_KEY_LEN		32
-
-/* See the SNP spec version 0.9 for secrets page format */
-struct snp_secrets_page_layout {
-	u32 version;
-	u32 imien	: 1,
-	    rsvd1	: 31;
-	u32 fms;
-	u32 rsvd2;
-	u8 gosvw[16];
-	u8 vmpck0[VMPCK_KEY_LEN];
-	u8 vmpck1[VMPCK_KEY_LEN];
-	u8 vmpck2[VMPCK_KEY_LEN];
-	u8 vmpck3[VMPCK_KEY_LEN];
-	struct secrets_os_area os_area;
-	u8 rsvd3[3840];
-} __packed;
-
 #endif /* __VIRT_SEVGUEST_H__ */
-- 
2.25.1

Re: [PATCH] x86/sev: get the AP jump table address from secrets page

[Borislav Petkov]

On Wed, Apr 20, 2022 at 10:27:51AM -0500, Michael Roth wrote:
> +static u64 get_secrets_page(void)
> +{
> +	u64 pa_data = boot_params.cc_blob_address;
> +	struct cc_blob_sev_info info;
> +	void *map;
> +
> +	/*
> +	 * The CC blob contains the address of the secrets page, check if the
> +	 * blob is present.
> +	 */
> +	if (!pa_data)
> +		return 0;
> +
> +	map = early_memremap(pa_data, sizeof(info));

That function can return NULL so you need to handle it.

> +	memcpy(&info, map, sizeof(info));
> +	early_memunmap(map, sizeof(info));
> +
> +	/* smoke-test the secrets page passed */
> +	if (!info.secrets_phys || info.secrets_len != PAGE_SIZE)
> +		return 0;
> +
> +	return info.secrets_phys;
> +}
> +
> +static u64 get_snp_jump_table_addr(void)
> +{
> +	struct snp_secrets_page_layout *layout;
> +	u64 pa = get_secrets_page();
> +	u64 addr;

Please don't hide the function call in the local variables declaration
but do this instead:

        struct snp_secrets_page_layout *layout;
        u64 pa, addr;

        pa = get_secrets_page();
        if (!pa)
                return 0;

Thx.

-- 
Regards/Gruss,
    Boris.

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