From: Joerg Roedel <jroedel@suse.de>
Date: Mon, 7 Sep 2020 15:16:09 +0200
Subject: x86/head/64: Don't call verify_cpu() on starting APs
Git-commit: 3ecacdbd23956a549d93023f86adc87b4a9d6520
Patch-mainline: v5.10-rc1
References: jsc#SLE-14337
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
---
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(+)
--- a/arch/x86/include/asm/realmode.h
+++ b/arch/x86/include/asm/realmode.h
@@ -73,6 +73,7 @@ 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)
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -123,6 +123,18 @@ ENTRY(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.
+ */
+ENTRY(secondary_startup_64_no_verify)
+ 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.
*/
--- a/arch/x86/realmode/init.c
+++ b/arch/x86/realmode/init.c
@@ -44,6 +44,12 @@ static void sme_sev_setup_real_mode(stru
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");
}