From: Ard Biesheuvel Date: Tue, 13 May 2025 11:11:59 +0000 (+0200) Subject: x86/boot: Defer initialization of VM space related global variables X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=64797551baec252f953fa8234051f88b0c368ed5;p=users%2Fdwmw2%2Flinux.git 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: Ard Biesheuvel Signed-off-by: Ingo Molnar Cc: Linus Torvalds Link: https://lore.kernel.org/r/20250513111157.717727-9-ardb+git@google.com --- diff --git a/arch/x86/boot/startup/map_kernel.c b/arch/x86/boot/startup/map_kernel.c index 099ae25593361..905e8734b5a31 100644 --- a/arch/x86/boot/startup/map_kernel.c +++ b/arch/x86/boot/startup/map_kernel.c @@ -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; } diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c index 510fb41f55fce..14f7dda20954b 100644 --- a/arch/x86/kernel/head64.c +++ b/arch/x86/kernel/head64.c @@ -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(); /*