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From:   Joerg Roedel <joro@8bytes.org>
To:     x86@kernel.org
Cc:     Joerg Roedel <joro@8bytes.org>, Joerg Roedel <jroedel@suse.de>,
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        Mike Stunes <mstunes@vmware.com>,
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Subject: [PATCH 1/7] x86/boot/compressed/64: Cleanup exception handling before booting kernel
Date:   Wed, 10 Feb 2021 11:21:29 +0100
Message-Id: <20210210102135.30667-2-joro@8bytes.org>
In-Reply-To: <20210210102135.30667-1-joro@8bytes.org>
References: <20210210102135.30667-1-joro@8bytes.org>
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From: Joerg Roedel <jroedel@suse.de>

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>
---
 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 804a502ee0d2..9b93567d663a 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 267e7f93050e..cc9fd0e8766a 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 901ea5ebec22..e5612f035498 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);
-- 
2.30.0