x86/head/64: Don't call verify_cpu() on starting APs

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

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20200907131613.12703-69-joro@8bytes.org

diff --git a/arch/x86/include/asm/realmode.h b/arch/x86/include/asm/realmode.h
index 4d4d853..5db5d08 100644 (file)
--- 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 1a71d0d..7eb2a1c 100644 (file)
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -126,6 +126,18 @@ SYM_CODE_START(secondary_startup_64)
        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 3fb9b60..22fda7d 100644 (file)
--- 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");
        }