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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=HgLY0RjcX26UI051X7p0jTvCIxdqYVMTsc8814Yedfgp0bzVK7UFbv8tvL3cLRx6u iDWC3D+nLEDNCb2TZLk5lDi5Udldgc4oVV5EETWkYfWURPnuXnXWyavWHFha+ew//E 2S5LwNp+WnBIoW+zr84x3BSUsI6BHHiVLKyfK5Og= Message-ID: <382872b6-748b-41de-b3f5-728964bbd82a@arm.com> Date: Wed, 29 Apr 2026 15:52:33 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 10/15] arm64: Move fixmap page tables to end of kernel image To: Ard Biesheuvel , 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 , Ryan Roberts , Anshuman Khandual , Liz Prucka , Seth Jenkins , Kees Cook , Mike Rapoport , David Hildenbrand , Andrew Morton , linux-mm@kvack.org, linux-hardening@vger.kernel.org References: <20260427153416.2103979-17-ardb+git@google.com> <20260427153416.2103979-27-ardb+git@google.com> From: Kevin Brodsky Content-Language: en-GB In-Reply-To: <20260427153416.2103979-27-ardb+git@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 4F1EDC0002 X-Stat-Signature: oikj3jfhzs6d7roqnojs9g9d93hkptae X-HE-Tag: 1777470760-107388 X-HE-Meta: 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 kFPOWLhu 9R1Y4haw1hExyGU6H4x571OXQhYNLeQN7AQl6pKWvZjTzk6gPaIRo5DaaNwWlT/eGuELge4XnE7WecjR+nyTsWLWHCjTvXSUaG34zC+bHmeb27401kin5QSp2Knt070ILV3p5IV9+fCSpbZXTr+t829eZb7egjSpB243+D1bGa2WgHG5pknRFAXjEjLt6f1faPr190b7ILhatxt4XPV6dacgRReY4hlrw6dTu26QjWqMgIQGKcPNH4PtjIDtQ5YwXN1B+ZKsQcPgn0NgQD2c9l760fvSfhKQhtKp0POSPfv9xVypFK8rN9/PKeRrN9xVqV6dykkvlJmvxx+IfizKLa2tSdyEtaaNLFoKF6TcJDPBGCDYY7qS0PuFNmuMpLcJEC+RbPaAQQJqe2xY= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 27/04/2026 17:34, Ard Biesheuvel wrote: > From: Ard Biesheuvel > > 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 Reviewed-by: Kevin Brodsky > --- > arch/arm64/kernel/vmlinux.lds.S | 5 +++++ > arch/arm64/mm/fixmap.c | 7 ++++--- > 2 files changed, 9 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S > index e1ac876200a3..2dca18574619 100644 > --- a/arch/arm64/kernel/vmlinux.lds.S > +++ b/arch/arm64/kernel/vmlinux.lds.S > @@ -353,6 +353,11 @@ SECTIONS > __pi___bss_start = __bss_start; > > . = ALIGN(PAGE_SIZE); > + .fixmap_pgdir : { > + __fixmap_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 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) > {