Commit 64797551 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Ingo Molnar
Browse files

x86/boot: Defer initialization of VM space related global variables 



The global pseudo-constants 'page_offset_base', 'vmalloc_base' and
'vmemmap_base' are not used extremely early during the boot, and cannot be
used safely until after the KASLR memory randomization code in
kernel_randomize_memory() executes, which may update their values.

So there is no point in setting these variables extremely early, and it
can wait until after the kernel itself is mapped and running from its
permanent virtual mapping.

Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20250513111157.717727-9-ardb+git@google.com
parent 891d3b8b

arch/x86/boot/startup/map_kernel.c

+0 −3
Original line number Diff line number Diff line
@@ -29,9 +29,6 @@ static inline bool check_la57_support(void) 
	__pgtable_l5_enabled	= 1;

	pgdir_shift		= 48;

	ptrs_per_p4d		= 512;

	page_offset_base	= __PAGE_OFFSET_BASE_L5;

	vmalloc_base		= __VMALLOC_BASE_L5;

	vmemmap_base		= __VMEMMAP_BASE_L5;



	return true;

}

arch/x86/kernel/head64.c

+6 −3
Original line number Diff line number Diff line
@@ -62,13 +62,10 @@ EXPORT_SYMBOL(ptrs_per_p4d); 
#ifdef CONFIG_DYNAMIC_MEMORY_LAYOUT

unsigned long page_offset_base __ro_after_init = __PAGE_OFFSET_BASE_L4;

EXPORT_SYMBOL(page_offset_base);

SYM_PIC_ALIAS(page_offset_base);

unsigned long vmalloc_base __ro_after_init = __VMALLOC_BASE_L4;

EXPORT_SYMBOL(vmalloc_base);

SYM_PIC_ALIAS(vmalloc_base);

unsigned long vmemmap_base __ro_after_init = __VMEMMAP_BASE_L4;

EXPORT_SYMBOL(vmemmap_base);

SYM_PIC_ALIAS(vmemmap_base);

#endif



/* Wipe all early page tables except for the kernel symbol map */
@@ -244,6 +241,12 @@ asmlinkage __visible void __init __noreturn x86_64_start_kernel(char * real_mode 
	/* Kill off the identity-map trampoline */

	reset_early_page_tables();



	if (pgtable_l5_enabled()) {

		page_offset_base	= __PAGE_OFFSET_BASE_L5;

		vmalloc_base		= __VMALLOC_BASE_L5;

		vmemmap_base		= __VMEMMAP_BASE_L5;

	}



	clear_bss();



	/*