From: "Ard Biesheuvel" <ardb@kernel•org>
To: "Kevin Brodsky" <kevin.brodsky@arm•com>,
"Ard Biesheuvel" <ardb+git@google•com>,
linux-arm-kernel@lists•infradead.org
Cc: linux-kernel@vger•kernel.org, "Will Deacon" <will@kernel•org>,
"Catalin Marinas" <catalin.marinas@arm•com>,
"Mark Rutland" <mark.rutland@arm•com>,
"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 13:19:29 +0200 [thread overview]
Message-ID: <96a8b6b9-71f2-4550-bbbb-fbfa146f4e6a@app.fastmail.com> (raw)
In-Reply-To: <2a6f9f05-ac57-4ef8-9328-74cc8ccfea16@arm.com>
On Fri, 29 May 2026, at 10:27, Kevin Brodsky wrote:
> 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?
Yes, otherwise it is emitted as PROGBITS, resulting in all of BSS to be
emitted into Image.
next prev parent reply other threads:[~2026-05-29 11:20 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
2026-05-29 11:19 ` Ard Biesheuvel [this message]
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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