From: Joerg Roedel <jroedel@suse.de>
Date: Wed, 10 Mar 2021 09:43:19 +0100
Subject: x86/boot/compressed/64: Cleanup exception handling before booting
 kernel
Git-commit: b099155e2df7dadf8b1ad9828158b89f5639f654
Patch-mainline: v5.13-rc1
References: jsc#SLE-14337

Disable the exception handling before booting the kernel to make sure
any exceptions that happen during early kernel boot are not directed to
the pre-decompression code.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210312123824.306-2-joro@8bytes.org
---
 arch/x86/boot/compressed/idt_64.c |   14 ++++++++++++++
 arch/x86/boot/compressed/misc.c   |    7 ++-----
 arch/x86/boot/compressed/misc.h   |    6 ++++++
 3 files changed, 22 insertions(+), 5 deletions(-)

--- a/arch/x86/boot/compressed/idt_64.c
+++ b/arch/x86/boot/compressed/idt_64.c
@@ -52,3 +52,17 @@ void load_stage2_idt(void)
 
 	load_boot_idt(&boot_idt_desc);
 }
+
+void cleanup_exception_handling(void)
+{
+	/*
+	 * Flush GHCB from cache and map it encrypted again when running as
+	 * SEV-ES guest.
+	 */
+	sev_es_shutdown_ghcb();
+
+	/* Set a null-idt, disabling #PF and #VC handling */
+	boot_idt_desc.size    = 0;
+	boot_idt_desc.address = 0;
+	load_boot_idt(&boot_idt_desc);
+}
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -442,11 +442,8 @@ asmlinkage __visible void *extract_kerne
 	handle_relocations(output, output_len, virt_addr);
 	debug_putstr("done.\nBooting the kernel.\n");
 
-	/*
-	 * Flush GHCB from cache and map it encrypted again when running as
-	 * SEV-ES guest.
-	 */
-	sev_es_shutdown_ghcb();
+	/* Disable exception handling before booting the kernel */
+	cleanup_exception_handling();
 
 	return output;
 }
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -154,6 +154,12 @@ extern pteval_t __default_kernel_pte_mas
 extern gate_desc boot_idt[BOOT_IDT_ENTRIES];
 extern struct desc_ptr boot_idt_desc;
 
+#ifdef CONFIG_X86_64
+void cleanup_exception_handling(void);
+#else
+static inline void cleanup_exception_handling(void) { }
+#endif
+
 /* IDT Entry Points */
 void boot_page_fault(void);
 void boot_stage1_vc(void);