Commit ca0e22d4 authored by Joerg Roedel's avatar Joerg Roedel Committed by Borislav Petkov
Browse files

x86/boot/compressed/64: Always switch to own page table 



When booted through startup_64(), the kernel keeps running on the EFI
page table until the KASLR code sets up its own page table. Without
KASLR, the pre-decompression boot code never switches off the EFI page
table. Change that by unconditionally switching to a kernel-controlled
page table after relocation.

This makes sure the kernel can make changes to the mapping when
necessary, for example map pages unencrypted in SEV and SEV-ES guests.

Also, remove the debug_putstr() calls in initialize_identity_maps()
because the function now runs before console_init() is called.

 [ bp: Massage commit message. ]

Signed-off-by: default avatarJoerg Roedel <jroedel@suse.de>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Reviewed-by: default avatarKees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20200907131613.12703-17-joro@8bytes.org
parent 8b0d3b3b

arch/x86/boot/compressed/head_64.S

+2 −1
Original line number Diff line number Diff line
@@ -543,10 +543,11 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated) 
	rep	stosq



/*

 * Load stage2 IDT

 * Load stage2 IDT and switch to our own page-table

 */

	pushq	%rsi

	call	load_stage2_idt

	call	initialize_identity_maps

	popq	%rsi



/*

arch/x86/boot/compressed/ident_map_64.c

+30 −21
Original line number Diff line number Diff line
@@ -86,9 +86,31 @@ phys_addr_t physical_mask = (1ULL << __PHYSICAL_MASK_SHIFT) - 1; 
 */

static struct x86_mapping_info mapping_info;



/*

 * Adds the specified range to what will become the new identity mappings.

 * Once all ranges have been added, the new mapping is activated by calling

 * finalize_identity_maps() below.

 */

void add_identity_map(unsigned long start, unsigned long size)

{

	unsigned long end = start + size;



	/* Align boundary to 2M. */

	start = round_down(start, PMD_SIZE);

	end = round_up(end, PMD_SIZE);

	if (start >= end)

		return;



	/* Build the mapping. */

	kernel_ident_mapping_init(&mapping_info, (pgd_t *)top_level_pgt,

				  start, end);

}



/* Locates and clears a region for a new top level page table. */

void initialize_identity_maps(void)

{

	unsigned long start, size;



	/* If running as an SEV guest, the encryption mask is required. */

	set_sev_encryption_mask();
@@ -121,37 +143,24 @@ void initialize_identity_maps(void) 
	 */

	top_level_pgt = read_cr3_pa();

	if (p4d_offset((pgd_t *)top_level_pgt, 0) == (p4d_t *)_pgtable) {

		debug_putstr("booted via startup_32()\n");

		pgt_data.pgt_buf = _pgtable + BOOT_INIT_PGT_SIZE;

		pgt_data.pgt_buf_size = BOOT_PGT_SIZE - BOOT_INIT_PGT_SIZE;

		memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);

	} else {

		debug_putstr("booted via startup_64()\n");

		pgt_data.pgt_buf = _pgtable;

		pgt_data.pgt_buf_size = BOOT_PGT_SIZE;

		memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);

		top_level_pgt = (unsigned long)alloc_pgt_page(&pgt_data);

	}

}



	/*

 * Adds the specified range to what will become the new identity mappings.

 * Once all ranges have been added, the new mapping is activated by calling

 * finalize_identity_maps() below.

	 * New page-table is set up - map the kernel image and load it

	 * into cr3.

	 */

void add_identity_map(unsigned long start, unsigned long size)

{

	unsigned long end = start + size;



	/* Align boundary to 2M. */

	start = round_down(start, PMD_SIZE);

	end = round_up(end, PMD_SIZE);

	if (start >= end)

		return;



	/* Build the mapping. */

	kernel_ident_mapping_init(&mapping_info, (pgd_t *)top_level_pgt,

				  start, end);

	start = (unsigned long)_head;

	size  = _end - _head;

	add_identity_map(start, size);

	write_cr3(top_level_pgt);

}



/*

arch/x86/boot/compressed/kaslr.c

+0 −3
Original line number Diff line number Diff line
@@ -861,9 +861,6 @@ void choose_random_location(unsigned long input, 


	boot_params->hdr.loadflags |= KASLR_FLAG;



	/* Prepare to add new identity pagetables on demand. */

	initialize_identity_maps();



	if (IS_ENABLED(CONFIG_X86_32))

		mem_limit = KERNEL_IMAGE_SIZE;

	else

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