[PATCH v7 68/72] x86/head/64: Don't call verify_cpu() on starting APs

Joerg Roedel
2020-09-07T13:16:09Z

The APs are not ready to handle exceptions when verify_cpu() is called
in secondary_startup_64.

Signed-off-by: Joerg Roedel <jroedel at suse.de>
Reviewed-by: Kees Cook <keescook at chromium.org>
---
 arch/x86/include/asm/realmode.h |  1 +
 arch/x86/kernel/head_64.S       | 12 ++++++++++++
 arch/x86/realmode/init.c        |  6 ++++++
 3 files changed, 19 insertions(+)

diff --git a/arch/x86/include/asm/realmode.h b/arch/x86/include/asm/realmode.h
index 4d4d853f6841..5db5d083c873 100644
--- a/arch/x86/include/asm/realmode.h
+++ b/arch/x86/include/asm/realmode.h
@@ -72,6 +72,7 @@ extern unsigned char startup_32_smp[];
 extern unsigned char boot_gdt[];
 #else
 extern unsigned char secondary_startup_64[];
+extern unsigned char secondary_startup_64_no_verify[];
 #endif

 static inline size_t real_mode_size_needed(void)
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 41057ff79284..d976a9e6fcba 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -125,6 +125,18 @@ SYM_CODE_START(secondary_startup_64)
 	/* Sanitize CPU configuration */
 	call verify_cpu

+	/*
+	 * The secondary_startup_64_no_verify entry point is only used by
+	 * SEV-ES guests. In those guests the call to verify_cpu() would cause
+	 * #VC exceptions which can not be handled at this stage of secondary
+	 * CPU bringup.
+	 *
+	 * All non SEV-ES systems, especially Intel systems, need to execute
+	 * verify_cpu() above to make sure NX is enabled.
+	 */
+SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL)
+	UNWIND_HINT_EMPTY
+
 	/*
 	 * Retrieve the modifier (SME encryption mask if SME is active) to be
 	 * added to the initial pgdir entry that will be programmed into CR3.
diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c
index 3fb9b60be07a..22fda7d99159 100644
--- a/arch/x86/realmode/init.c
+++ b/arch/x86/realmode/init.c
@@ -46,6 +46,12 @@ static void sme_sev_setup_real_mode(struct trampoline_header
*th)
 		th->flags |= TH_FLAGS_SME_ACTIVE;

 	if (sev_es_active()) {
+		/*
+		 * Skip the call to verify_cpu() in secondary_startup_64 as it
+		 * will cause #VC exceptions when the AP can't handle them yet.
+		 */
+		th->start = (u64) secondary_startup_64_no_verify;
+
 		if (sev_es_setup_ap_jump_table(real_mode_header))
 			panic("Failed to get/update SEV-ES AP Jump Table");
 	}
--
2.28.0