From: Kevin Brodsky <kevin.brodsky@arm•com>
To: Ard Biesheuvel <ardb+git@google•com>,
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,
linuxppc-dev@lists•ozlabs.org, linux-sh@vger•kernel.org
Subject: Re: [PATCH v6 09/15] arm64: Move fixmap and kasan page tables to end of kernel image
Date: Fri, 29 May 2026 10:27:37 +0200 [thread overview]
Message-ID: <2a6f9f05-ac57-4ef8-9328-74cc8ccfea16@arm.com> (raw)
In-Reply-To: <20260526175846.2694125-26-ardb+git@google.com>
On 26/05/2026 19:58, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@kernel•org>
>
> Move the fixmap and kasan 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/include/asm/mmu.h | 2 ++
> arch/arm64/kernel/vmlinux.lds.S | 8 +++++++-
> arch/arm64/mm/fixmap.c | 6 +++---
> arch/arm64/mm/kasan_init.c | 2 +-
> 4 files changed, 13 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
> index 5e1211c540ab..fb95754f2876 100644
> --- a/arch/arm64/include/asm/mmu.h
> +++ b/arch/arm64/include/asm/mmu.h
> @@ -13,6 +13,8 @@
>
> #ifndef __ASSEMBLER__
>
> +#define __pgtbl_bss __section(".pgdir.bss") __aligned(PAGE_SIZE)
> +
> #include <linux/refcount.h>
> #include <asm/cpufeature.h>
>
> diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
> index e1ac876200a3..2b0ebfb30c63 100644
> --- a/arch/arm64/kernel/vmlinux.lds.S
> +++ b/arch/arm64/kernel/vmlinux.lds.S
> @@ -349,9 +349,15 @@ 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;
>
> + /* fixmap BSS starts here - preceding data/BSS is omitted from the linear map */
> + .pgdir.bss (NOLOAD) : ALIGN(PAGE_SIZE) {
Do we actually need the NOLOAD type here?
Aside from that:
Reviewed-by: Kevin Brodsky <kevin.brodsky@arm•com>
> + *(.pgdir.bss)
> + }
> + ASSERT(ADDR(.pgdir.bss) == __bss_stop, ".pgdir.bss must follow BSS")
> +
> . = ALIGN(PAGE_SIZE);
> __pi_init_pg_dir = .;
> . += INIT_DIR_SIZE;
> diff --git a/arch/arm64/mm/fixmap.c b/arch/arm64/mm/fixmap.c
> index c5c5425791da..1a3bbd67dd76 100644
> --- a/arch/arm64/mm/fixmap.c
> +++ b/arch/arm64/mm/fixmap.c
> @@ -31,9 +31,9 @@ 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;
> +static pte_t bm_pte[NR_BM_PTE_TABLES][PTRS_PER_PTE] __pgtbl_bss;
> +static pmd_t bm_pmd[PTRS_PER_PMD] __pgtbl_bss __maybe_unused;
> +static pud_t bm_pud[PTRS_PER_PUD] __pgtbl_bss __maybe_unused;
>
> static inline pte_t *fixmap_pte(unsigned long addr)
> {
> diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c
> index abeb81bf6ebd..dbf22cae82ee 100644
> --- a/arch/arm64/mm/kasan_init.c
> +++ b/arch/arm64/mm/kasan_init.c
> @@ -214,7 +214,7 @@ asmlinkage void __init kasan_early_init(void)
> * shadow pud_t[]/p4d_t[], which could end up getting corrupted
> * when the linear region is mapped.
> */
> - static pte_t tbl[PTRS_PER_PTE] __page_aligned_bss;
> + static pte_t tbl[PTRS_PER_PTE] __pgtbl_bss;
> pgd_t *pgdp = pgd_offset_k(KASAN_SHADOW_START);
>
> set_pgd(pgdp, __pgd(__pa_symbol(tbl) | PGD_TYPE_TABLE));
next prev parent reply other threads:[~2026-05-29 8:27 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-26 17:58 [PATCH v6 00/15] arm64: Unmap linear alias of kernel data/bss Ard Biesheuvel
2026-05-26 17:58 ` [PATCH v6 01/15] arm64: mm: Remove bogus stop condition from map_mem() loop Ard Biesheuvel
2026-05-26 17:58 ` [PATCH v6 02/15] arm64: mm: Drop redundant pgd_t* argument from map_mem() Ard Biesheuvel
2026-05-26 17:58 ` [PATCH v6 03/15] arm64: mm: Check for pud_/pmd_set_huge() failures on kernel mappings Ard Biesheuvel
2026-05-26 17:58 ` [PATCH v6 04/15] arm64: mm: Preserve existing table mappings when mapping DRAM Ard Biesheuvel
2026-05-26 17:58 ` [PATCH v6 05/15] arm64: mm: Preserve non-contiguous descriptors " Ard Biesheuvel
2026-05-26 17:58 ` [PATCH v6 06/15] arm64: mm: Permit contiguous descriptors to be manipulated Ard Biesheuvel
2026-05-26 17:58 ` [PATCH v6 07/15] arm64: kfence: Avoid NOMAP tricks when mapping the early pool Ard Biesheuvel
2026-05-29 8:25 ` Kevin Brodsky
2026-05-26 17:58 ` [PATCH v6 08/15] arm64: mm: Permit contiguous attribute for preliminary mappings Ard Biesheuvel
2026-05-29 8:25 ` Kevin Brodsky
2026-05-26 17:58 ` [PATCH v6 09/15] arm64: Move fixmap and kasan page tables to end of kernel image Ard Biesheuvel
2026-05-29 8:27 ` Kevin Brodsky [this message]
2026-05-29 11:19 ` Ard Biesheuvel
2026-05-29 14:42 ` Kevin Brodsky
2026-05-29 14:47 ` Ard Biesheuvel
2026-06-01 8:37 ` Kevin Brodsky
2026-06-01 8:39 ` Ard Biesheuvel
2026-05-26 17:58 ` [PATCH v6 10/15] arm64: mm: Don't abuse memblock NOMAP to check for overlaps Ard Biesheuvel
2026-05-29 8:28 ` Kevin Brodsky
2026-05-26 17:58 ` [PATCH v6 11/15] arm64: mm: Map the kernel data/bss read-only in the linear map Ard Biesheuvel
2026-05-29 8:28 ` Kevin Brodsky
2026-05-26 17:58 ` [PATCH v6 12/15] powerpc/code-patching: Avoid r/w mapping of the zero page Ard Biesheuvel
2026-05-26 17:59 ` [PATCH v6 13/15] sh: cast away constness from the zero page when flushing it from the cache Ard Biesheuvel
2026-05-27 9:31 ` Geert Uytterhoeven
2026-05-28 5:46 ` Mike Rapoport
2026-05-28 6:14 ` Ard Biesheuvel
2026-05-26 17:59 ` [PATCH v6 14/15] mm: Make empty_zero_page[] const Ard Biesheuvel
2026-05-26 17:59 ` [PATCH v6 15/15] arm64: mm: Unmap kernel data/bss entirely from the linear map Ard Biesheuvel
2026-05-29 8:29 ` Kevin Brodsky
2026-05-29 8:34 ` Ard Biesheuvel
2026-05-29 8:49 ` Kevin Brodsky
2026-05-29 11:48 ` Ard Biesheuvel
2026-05-29 8:31 ` [PATCH v6 00/15] arm64: Unmap linear alias of kernel data/bss Kevin Brodsky
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