x86/boot/compressed/64: Add page-fault handler

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@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20200907131613.12703-16-joro@8bytes.org

diff --git a/arch/x86/boot/compressed/ident_map_64.c b/arch/x86/boot/compressed/ident_map_64.c
index d9932a1..e3d980a 100644 (file)
--- a/arch/x86/boot/compressed/ident_map_64.c
+++ b/arch/x86/boot/compressed/ident_map_64.c
@@ -19,10 +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 <linux/pgtable.h>
+#include <asm/trap_pf.h>
+#include <asm/trapnr.h>
 #include <asm/init.h>
 /* Use the static base for this part of the boot process */
 #undef __PAGE_OFFSET
@@ -160,3 +163,39 @@ void finalize_identity_maps(void)
 {
        write_cr3(top_level_pgt);
 }
+
+static void do_pf_error(const char *msg, unsigned long error_code,
+                       unsigned long address, unsigned long ip)
+{
+       error_putstr(msg);
+
+       error_putstr("\nError Code: ");
+       error_puthex(error_code);
+       error_putstr("\nCR2: 0x");
+       error_puthex(address);
+       error_putstr("\nRIP relative to _head: 0x");
+       error_puthex(ip - (unsigned long)_head);
+       error_putstr("\n");
+
+       error("Stopping.\n");
+}
+
+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))
+               do_pf_error("Unexpected page-fault:", error_code, address, regs->ip);
+
+       /*
+        * 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 082cd6b..5f08309 100644 (file)
--- a/arch/x86/boot/compressed/idt_64.c
+++ b/arch/x86/boot/compressed/idt_64.c
@@ -40,5 +40,7 @@ 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 36dee2f..b20e575 100644 (file)
--- a/arch/x86/boot/compressed/idt_handlers_64.S
+++ b/arch/x86/boot/compressed/idt_handlers_64.S
@@ -68,3 +68,5 @@ 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 98b7a1d..f0e1991 100644 (file)
--- 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 */