From: Joerg Roedel <jroe...@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 <jroe...@suse.de> Reviewed-by: Kees Cook <keesc...@chromium.org> Link: https://lore.kernel.org/r/20200724160336.5435-15-j...@8bytes.org --- arch/x86/boot/compressed/ident_map_64.c | 39 ++++++++++++++++++++++ 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, 49 insertions(+) diff --git a/arch/x86/boot/compressed/ident_map_64.c b/arch/x86/boot/compressed/ident_map_64.c index d9932a133ac9..e3d980ae9c2b 100644 --- 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 082cd6bca033..5f083092a86d 100644 --- 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 36dee2f40a8b..b20e57504a94 100644 --- 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 98b7a1df9c59..f0e199174c5f 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 */ -- 2.28.0 _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization
