[PATCH v3 15/75] x86/boot/compressed/64: Add page-fault handler

Joerg Roedel
Tue, 28 Apr 2020 15:16:25 -0000

From: Joerg Roedel <jroedel at suse.de>

Install a page-fault handler to add an identity mapping to addresses
not yet mapped. Also do some checking whether the error code is sane.

This makes non SEV-ES machines use the exception handling
infrastructure in the pre-decompressions boot code too, making it less
likely to break in the future.

Signed-off-by: Joerg Roedel <jroedel at suse.de>
---
 arch/x86/boot/compressed/ident_map_64.c    | 33 ++++++++++++++++++++++
 arch/x86/boot/compressed/idt_64.c          |  2 ++
 arch/x86/boot/compressed/idt_handlers_64.S |  2 ++
 arch/x86/boot/compressed/misc.h            |  6 ++++
 4 files changed, 43 insertions(+)

diff --git a/arch/x86/boot/compressed/ident_map_64.c
b/arch/x86/boot/compressed/ident_map_64.c
index 3a2115582920..33bdf923cbab 100644
--- a/arch/x86/boot/compressed/ident_map_64.c
+++ b/arch/x86/boot/compressed/ident_map_64.c
@@ -19,11 +19,13 @@
 /* No PAGE_TABLE_ISOLATION support needed either: */
 #undef CONFIG_PAGE_TABLE_ISOLATION

+#include "error.h"
 #include "misc.h"

 /* These actually do the work of building the kernel identity maps. */
 #include <asm/init.h>
 #include <asm/pgtable.h>
+#include <asm/trap_defs.h>
 /* Use the static base for this part of the boot process */
 #undef __PAGE_OFFSET
 #define __PAGE_OFFSET __PAGE_OFFSET_BASE
@@ -163,3 +165,34 @@ void finalize_identity_maps(void)
 {
 	write_cr3(top_level_pgt);
 }
+
+void do_boot_page_fault(struct pt_regs *regs, unsigned long error_code)
+{
+	unsigned long address = native_read_cr2();
+
+	/*
+	 * Check for unexpected error codes. Unexpected are:
+	 *	- Faults on present pages
+	 *	- User faults
+	 *	- Reserved bits set
+	 */
+	if (error_code & (X86_PF_PROT | X86_PF_USER | X86_PF_RSVD)) {
+		/* Print some information for debugging */
+		error_putstr("Unexpected page-fault:");
+		error_putstr("\nError Code: ");
+		error_puthex(error_code);
+		error_putstr("\nCR2: 0x");
+		error_puthex(address);
+		error_putstr("\nRIP relative to _head: 0x");
+		error_puthex(regs->ip - (unsigned long)_head);
+		error_putstr("\n");
+
+		error("Stopping.\n");
+	}
+
+	/*
+	 * Error code is sane - now identity map the 2M region around
+	 * the faulting address.
+	 */
+	add_identity_map(address & PMD_MASK, PMD_SIZE);
+}
diff --git a/arch/x86/boot/compressed/idt_64.c
b/arch/x86/boot/compressed/idt_64.c
index 46ecea671b90..99cc78062684 100644
--- a/arch/x86/boot/compressed/idt_64.c
+++ b/arch/x86/boot/compressed/idt_64.c
@@ -39,5 +39,7 @@ void load_stage2_idt(void)
 {
 	boot_idt_desc.address = (unsigned long)boot_idt;

+	set_idt_entry(X86_TRAP_PF, boot_page_fault);
+
 	load_boot_idt(&boot_idt_desc);
 }
diff --git a/arch/x86/boot/compressed/idt_handlers_64.S
b/arch/x86/boot/compressed/idt_handlers_64.S
index f86ea872d860..eda50cbdafa0 100644
--- a/arch/x86/boot/compressed/idt_handlers_64.S
+++ b/arch/x86/boot/compressed/idt_handlers_64.S
@@ -67,3 +67,5 @@ SYM_FUNC_END(\name)

 	.text
 	.code64
+
+EXCEPTION_HANDLER	boot_page_fault do_boot_page_fault error_code=1
diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index 3a030a878d53..345c90fbc500 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -37,6 +37,9 @@
 #define memptr unsigned
 #endif

+/* boot/compressed/vmlinux start and end markers */
+extern char _head[], _end[];
+
 /* misc.c */
 extern memptr free_mem_ptr;
 extern memptr free_mem_end_ptr;
@@ -146,4 +149,7 @@ extern pteval_t __default_kernel_pte_mask;
 extern gate_desc boot_idt[BOOT_IDT_ENTRIES];
 extern struct desc_ptr boot_idt_desc;

+/* IDT Entry Points */
+void boot_page_fault(void);
+
 #endif /* BOOT_COMPRESSED_MISC_H */
--
2.17.1