From: Ard Biesheuvel <ardb+git@google.com>
To: linux-kernel@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org, will@kernel.org,
catalin.marinas@arm.com, mark.rutland@arm.com,
Ard Biesheuvel <ardb@kernel.org>,
Ryan Roberts <ryan.roberts@arm.com>,
Anshuman Khandual <anshuman.khandual@arm.com>,
Liz Prucka <lizprucka@google.com>,
Seth Jenkins <sethjenkins@google.com>,
Kees Cook <kees@kernel.org>,
linux-hardening@vger.kernel.org
Subject: [PATCH v3 10/13] arm64: Move fixmap page tables to end of kernel image
Date: Fri, 20 Mar 2026 15:59:45 +0100 [thread overview]
Message-ID: <20260320145934.2349881-25-ardb+git@google.com> (raw)
In-Reply-To: <20260320145934.2349881-15-ardb+git@google.com>
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 | 5 +++--
2 files changed, 8 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index 2d021a576e50..282516def39c 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 c3dd3c868cf5..30aba998cf38 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)
+#define __fixmap_bss __section(".fixmap_bss") __aligned(PAGE_SIZE)
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;
+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)
{
--
2.53.0.959.g497ff81fa9-goog
next prev parent reply other threads:[~2026-03-20 15:00 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-20 14:59 [PATCH v3 00/13] arm64: Unmap linear alias of kernel data/bss Ard Biesheuvel
2026-03-20 14:59 ` [PATCH v3 01/13] arm64: Move the zero page to rodata Ard Biesheuvel
2026-03-20 14:59 ` [PATCH v3 02/13] arm64: mm: Preserve existing table mappings when mapping DRAM Ard Biesheuvel
2026-03-20 14:59 ` [PATCH v3 03/13] arm64: mm: Preserve non-contiguous descriptors " Ard Biesheuvel
2026-03-20 14:59 ` [PATCH v3 04/13] arm64: mm: Remove bogus stop condition from map_mem() loop Ard Biesheuvel
2026-03-20 14:59 ` [PATCH v3 05/13] arm64: mm: Drop redundant pgd_t* argument from map_mem() Ard Biesheuvel
2026-03-20 14:59 ` [PATCH v3 06/13] arm64: mm: Permit contiguous descriptors to be rewritten Ard Biesheuvel
2026-03-20 14:59 ` [PATCH v3 07/13] arm64: mm: Use hierarchical XN mapping for the fixmap Ard Biesheuvel
2026-03-20 14:59 ` [PATCH v3 08/13] arm64: kfence: Avoid NOMAP tricks when mapping the early pool Ard Biesheuvel
2026-03-20 14:59 ` [PATCH v3 09/13] arm64: mm: Permit contiguous attribute for preliminary mappings Ard Biesheuvel
2026-03-20 14:59 ` Ard Biesheuvel [this message]
2026-03-20 14:59 ` [PATCH v3 11/13] arm64: mm: Don't abuse memblock NOMAP to check for overlaps Ard Biesheuvel
2026-03-20 14:59 ` [PATCH v3 12/13] arm64: mm: Map the kernel data/bss read-only in the linear map Ard Biesheuvel
2026-03-20 14:59 ` [PATCH v3 13/13] arm64: mm: Unmap kernel data/bss entirely from " Ard Biesheuvel
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