From: "Ard Biesheuvel" <ardb@kernel.org>
To: "Catalin Marinas" <catalin.marinas@arm.com>,
"Ard Biesheuvel" <ardb+git@google.com>
Cc: linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
"Will Deacon" <will@kernel.org>,
"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>,
linux-hardening@vger.kernel.org
Subject: Re: [PATCH v3 01/13] arm64: Move the zero page to rodata
Date: Wed, 08 Apr 2026 17:09:26 +0200 [thread overview]
Message-ID: <52abb233-80c5-4363-871d-cd52667291ad@app.fastmail.com> (raw)
In-Reply-To: <adZbgYJqY6bisaoZ@arm.com>
On Wed, 8 Apr 2026, at 15:43, Catalin Marinas wrote:
> Hi Ard,
>
> On Fri, Mar 20, 2026 at 03:59:36PM +0100, Ard Biesheuvel wrote:
>> diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
>> index 2964aad0362e..2d021a576e50 100644
>> --- a/arch/arm64/kernel/vmlinux.lds.S
>> +++ b/arch/arm64/kernel/vmlinux.lds.S
>> @@ -229,6 +229,7 @@ SECTIONS
>> #endif
>>
>> reserved_pg_dir = .;
>> + empty_zero_page = .;
>> . += PAGE_SIZE;
>>
>> swapper_pg_dir = .;
>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>> index a6a00accf4f9..795743913ce5 100644
>> --- a/arch/arm64/mm/mmu.c
>> +++ b/arch/arm64/mm/mmu.c
>> @@ -66,9 +66,8 @@ long __section(".mmuoff.data.write") __early_cpu_boot_status;
>>
>> /*
>> * Empty_zero_page is a special page that is used for zero-initialized data
>> - * and COW.
>> + * and COW. Defined in the linker script.
>> */
>> -unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)] __page_aligned_bss;
>> EXPORT_SYMBOL(empty_zero_page);
>
> I looked at Sashiko's reports
> (https://sashiko.dev/#/patchset/20260320145934.2349881-15-ardb+git@google.com)
> and it has a point here that with MTE, map_mem() doesn't map the
> empty_zero_page as Tagged in the for_each_mem_range() loop. The
> subsequent cpu_enable_mte() will fail to initialise the tags. I think
> this problem disappears with patch 11 where all the linear map is now
> Tagged.
>
> We either ignore it or we temporarily map the kernel as Tagged until the
> linear alias is removed later:
>
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 795743913ce5..5290f7537074 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1175,7 +1175,7 @@ static void __init map_mem(pgd_t *pgdp)
> * so we should avoid them here.
> */
> __map_memblock(pgdp, kernel_start, kernel_end,
> - PAGE_KERNEL, NO_CONT_MAPPINGS);
> + pgprot_tagged(PAGE_KERNEL), NO_CONT_MAPPINGS);
> memblock_clear_nomap(kernel_start, kernel_end - kernel_start);
> arm64_kfence_map_pool(early_kfence_pool, pgdp);
> }
>
OK. There were some other very good comments too, I'll look into those and respin this for the next cycle.
next prev parent reply other threads:[~2026-04-08 15:09 UTC|newest]
Thread overview: 18+ 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
2026-04-08 13:43 ` Catalin Marinas
2026-04-08 15:09 ` Ard Biesheuvel [this message]
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
2026-04-08 15:45 ` Catalin Marinas
2026-04-08 15:48 ` 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 ` [PATCH v3 10/13] arm64: Move fixmap page tables to end of kernel image Ard Biesheuvel
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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