Subject: [PATCH v5 10/13] arm64: Move fixmap page tables to end of kernel image

From: Ard Biesheuvel <[email-masked]>
Date: Tue, 19 May 2026 17:16:27 +0200

From: Ard Biesheuvel <[email-masked]>

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.

Reviewed-by: Kevin Brodsky <[email-masked]>
Signed-off-by: Ard Biesheuvel <[email-masked]>
---
 arch/arm64/kernel/vmlinux.lds.S | 10 ++++++++--
 arch/arm64/mm/fixmap.c          |  7 ++++---
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index e1ac876200a3..64c7bf4b7176 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -349,10 +349,16 @@ SECTIONS
 	_edata = .;
 
 	/* start of zero-init region */
-	BSS_SECTION(SBSS_ALIGN, 0, 0)
+	BSS_SECTION(SBSS_ALIGN, 0, PAGE_SIZE)
 	__pi___bss_start = __bss_start;
 
-	. = ALIGN(PAGE_SIZE);
+	/* fixmap BSS starts here - preceding data/BSS is omitted from the linear map */
+	.fixmap_pgdir : ALIGN(PAGE_SIZE) {
+		*(.fixmap_bss)
+	}
+	ASSERT(ADDR(.fixmap_pgdir) == __bss_stop, ".fixmap_pgdir should follow 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)
 {
-- 
2.54.0.563.g4f69b47b94-goog