[tip: x86/seves] x86/boot/compressed/64: Cleanup exception handling before booting kernel

[tip-bot2 for Joerg Roedel]

The following commit has been merged into the x86/seves branch of tip:

Commit-ID:     b099155e2df7dadf8b1ad9828158b89f5639f654
Gitweb:        https://git.kernel.org/tip/b099155e2df7dadf8b1ad9828158b89f5639f654
Author:        Joerg Roedel <jroedel@xxxxxxx>
AuthorDate:    Wed, 10 Mar 2021 09:43:19 +01:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Thu, 18 Mar 2021 16:44:36 +01:00

x86/boot/compressed/64: Cleanup exception handling before booting kernel

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@xxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Link: https://lkml.kernel.org/r/20210312123824.306-2-joro@xxxxxxxxxx
---
 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(-)

diff --git a/arch/x86/boot/compressed/idt_64.c b/arch/x86/boot/compressed/idt_64.c
index 804a502..9b93567 100644
--- 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);
+}
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index 267e7f9..cc9fd0e 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -443,11 +443,8 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
 	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;
 }
diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index 901ea5e..e5612f0 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -155,6 +155,12 @@ extern pteval_t __default_kernel_pte_mask;
 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);