Commit f70b3a23 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Will Deacon
Browse files

arm64: head: create a temporary FDT mapping in the initial ID map 



We need to access the DT very early to get at the command line and the
KASLR seed, which currently means we rely on some hacks to call into the
kernel before really calling into the kernel, which is undesirable.

So instead, let's create a mapping for the FDT in the initial ID map,
which is feasible now that it has been extended to cover more than a
single page or block, and can be updated in place to remap other output
addresses.

Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20220624150651.1358849-15-ardb@kernel.org


Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent d7bea550

arch/arm64/include/asm/kernel-pgtable.h

+4 −2
Original line number Diff line number Diff line
@@ -8,6 +8,7 @@ 
#ifndef __ASM_KERNEL_PGTABLE_H

#define __ASM_KERNEL_PGTABLE_H



#include <asm/boot.h>

#include <asm/pgtable-hwdef.h>

#include <asm/sparsemem.h>
@@ -88,10 +89,11 @@ 


/* the initial ID map may need two extra pages if it needs to be extended */

#if VA_BITS < 48

#define INIT_IDMAP_DIR_SIZE	(INIT_DIR_SIZE + (2 * PAGE_SIZE))

#define INIT_IDMAP_DIR_SIZE	((INIT_IDMAP_DIR_PAGES + 2) * PAGE_SIZE)

#else

#define INIT_IDMAP_DIR_SIZE	INIT_DIR_SIZE

#define INIT_IDMAP_DIR_SIZE	(INIT_IDMAP_DIR_PAGES * PAGE_SIZE)

#endif

#define INIT_IDMAP_DIR_PAGES	EARLY_PAGES(KIMAGE_VADDR, _end + MAX_FDT_SIZE + SWAPPER_BLOCK_SIZE)



/* Initial memory map size */

#if ARM64_KERNEL_USES_PMD_MAPS

arch/arm64/kernel/head.S

+13 −1
Original line number Diff line number Diff line
@@ -83,6 +83,7 @@ 
	 *

	 *  Register   Scope                      Purpose

	 *  x21        primary_entry() .. start_kernel()        FDT pointer passed at boot in x0

	 *  x22        create_idmap() .. start_kernel()         ID map VA of the DT blob

	 *  x23        primary_entry() .. start_kernel()        physical misalignment/KASLR offset

	 *  x28        clear_page_tables()                      callee preserved temp register

	 *  x19/x20    __primary_switch()                       callee preserved temp registers
@@ -348,7 +349,7 @@ SYM_FUNC_START_LOCAL(create_idmap) 
#endif

	adrp	x0, init_idmap_pg_dir

	adrp	x3, _text

	adrp	x6, _end

	adrp	x6, _end + MAX_FDT_SIZE + SWAPPER_BLOCK_SIZE

	mov	x7, SWAPPER_RX_MMUFLAGS



	map_memory x0, x1, x3, x6, x7, x3, IDMAP_PGD_ORDER, x10, x11, x12, x13, x14, EXTRA_SHIFT
@@ -362,6 +363,17 @@ SYM_FUNC_START_LOCAL(create_idmap) 
	mov	x6, #SWAPPER_BLOCK_SHIFT

	bl	remap_region



	/* Remap the FDT after the kernel image */

	adrp	x1, _text

	adrp	x22, _end + SWAPPER_BLOCK_SIZE

	bic	x2, x22, #SWAPPER_BLOCK_SIZE - 1

	bfi	x22, x21, #0, #SWAPPER_BLOCK_SHIFT		// remapped FDT address

	add	x3, x2, #MAX_FDT_SIZE + SWAPPER_BLOCK_SIZE

	bic	x4, x21, #SWAPPER_BLOCK_SIZE - 1

	mov	x5, SWAPPER_RW_MMUFLAGS

	mov	x6, #SWAPPER_BLOCK_SHIFT

	bl	remap_region



	/*

	 * Since the page tables have been populated with non-cacheable

	 * accesses (MMU disabled), invalidate those tables again to