[PATCH v2 02/10] arm64: Move fixmap page tables to end of kernel image
From: Ard Biesheuvel <hidden>
Date: 2026-01-26 09:27:36
Also in:
linux-hardening, lkml
Subsystem:
arm64 port (aarch64 architecture), the rest · Maintainers:
Catalin Marinas, Will Deacon, Linus Torvalds
From: Ard Biesheuvel <ardb@kernel.org> Move the fixmap page tables out of the BSS section, and place them at the end of the image, right before the init_pg_dir section where some of the other statically allocated page tables live. These page tables are currently the only data objects in vmlinux that are meant to be accessed via the kernel image's linear alias, and so placing them together allows the remainder of the data/bss section to be remapped read-only or unmapped entirely. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> --- arch/arm64/kernel/vmlinux.lds.S | 5 +++++ arch/arm64/mm/fixmap.c | 7 ++++--- 2 files changed, 9 insertions(+), 3 deletions(-)
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index b2a093f5b3fc..c089b83308a5 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S@@ -335,6 +335,11 @@ SECTIONS __pi___bss_start = __bss_start; . = ALIGN(PAGE_SIZE); + .pgdir : { + __pgdir_start = .; + *(.fixmap_bss) + } + __pi_init_pg_dir = .; . += INIT_DIR_SIZE; __pi_init_pg_end = .;
diff --git a/arch/arm64/mm/fixmap.c b/arch/arm64/mm/fixmap.c
index c5c5425791da..b649ea1a46e4 100644
--- a/arch/arm64/mm/fixmap.c
+++ b/arch/arm64/mm/fixmap.c@@ -31,9 +31,10 @@ static_assert(NR_BM_PMD_TABLES == 1); #define BM_PTE_TABLE_IDX(addr) __BM_TABLE_IDX(addr, PMD_SHIFT) -static pte_t bm_pte[NR_BM_PTE_TABLES][PTRS_PER_PTE] __page_aligned_bss; -static pmd_t bm_pmd[PTRS_PER_PMD] __page_aligned_bss __maybe_unused; -static pud_t bm_pud[PTRS_PER_PUD] __page_aligned_bss __maybe_unused; +#define __fixmap_bss __section(".fixmap_bss") __aligned(PAGE_SIZE) +static pte_t bm_pte[NR_BM_PTE_TABLES][PTRS_PER_PTE] __fixmap_bss; +static pmd_t bm_pmd[PTRS_PER_PMD] __fixmap_bss __maybe_unused; +static pud_t bm_pud[PTRS_PER_PUD] __fixmap_bss __maybe_unused; static inline pte_t *fixmap_pte(unsigned long addr) {
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2.52.0.457.g6b5491de43-goog