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

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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
This commit is contained in:
Joerg Roedel 2020-09-07 15:15:16 +02:00 committed by Borislav Petkov
parent 5f2bb01682
commit 8b0d3b3b41
4 changed files with 49 additions and 0 deletions
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39
arch/x86/boot/compressed/ident_map_64.c
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@ -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);
}

2
arch/x86/boot/compressed/idt_64.c
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@ -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);
}

2
arch/x86/boot/compressed/idt_handlers_64.S
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@ -68,3 +68,5 @@ SYM_FUNC_END(\name)
.text
.code64
EXCEPTION_HANDLER boot_page_fault do_boot_page_fault error_code=1

6
arch/x86/boot/compressed/misc.h
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@ -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 */