From: Ard Biesheuvel <ardb+git@google.com>
To: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.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>, Mike Rapoport <rppt@kernel.org>,
David Hildenbrand <david@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Jann Horn <jannh@google.com>,
linux-mm@kvack.org, linux-hardening@vger.kernel.org,
Kevin Brodsky <kevin.brodsky@arm.com>
Subject: [PATCH v5 10/13] arm64: Move fixmap page tables to end of kernel image
Date: Tue, 19 May 2026 17:16:27 +0200 [thread overview]
Message-ID: <20260519151616.2557018-25-ardb+git@google.com> (raw)
In-Reply-To: <20260519151616.2557018-15-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.
Reviewed-by: Kevin Brodsky <kevin.brodsky@arm.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
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
next prev parent reply other threads:[~2026-05-19 15:19 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-19 15:16 [PATCH v5 00/13] arm64: Unmap linear alias of kernel data/bss Ard Biesheuvel
2026-05-19 15:16 ` [PATCH v5 01/13] arm64: mm: Map the linear alias of text/rodata as tagged Ard Biesheuvel
2026-05-19 15:16 ` [PATCH v5 02/13] mm: Make empty_zero_page[] const Ard Biesheuvel
2026-05-19 15:16 ` [PATCH v5 03/13] arm64: mm: Preserve existing table mappings when mapping DRAM Ard Biesheuvel
2026-05-19 15:16 ` [PATCH v5 04/13] arm64: mm: Preserve non-contiguous descriptors " Ard Biesheuvel
2026-05-19 15:16 ` [PATCH v5 05/13] arm64: mm: Remove bogus stop condition from map_mem() loop Ard Biesheuvel
2026-05-19 15:16 ` [PATCH v5 06/13] arm64: mm: Drop redundant pgd_t* argument from map_mem() Ard Biesheuvel
2026-05-19 15:16 ` [PATCH v5 07/13] arm64: mm: Permit contiguous descriptors to be rewritten Ard Biesheuvel
2026-05-19 15:16 ` [PATCH v5 08/13] arm64: kfence: Avoid NOMAP tricks when mapping the early pool Ard Biesheuvel
2026-05-19 15:16 ` [PATCH v5 09/13] arm64: mm: Permit contiguous attribute for preliminary mappings Ard Biesheuvel
2026-05-19 15:16 ` Ard Biesheuvel [this message]
2026-05-19 15:16 ` [PATCH v5 11/13] arm64: mm: Don't abuse memblock NOMAP to check for overlaps Ard Biesheuvel
2026-05-19 15:16 ` [PATCH v5 12/13] arm64: mm: Map the kernel data/bss read-only in the linear map Ard Biesheuvel
2026-05-19 15:16 ` [PATCH v5 13/13] arm64: mm: Unmap kernel data/bss entirely from " Ard Biesheuvel
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