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Thu, 27 Aug 2026 09:44:30 -0700 (PDT) Date: Thu, 27 Aug 2026 18:44:10 +0200 Mime-Version: 1.0 X-Developer-Key: i=ardb@kernel.org; a=openpgp; fpr=F43D03328115A198C90016883D200E9CA6329909 X-Developer-Signature: v=1; a=openpgp-sha256; l=1713; i=ardb@kernel.org; h=from:subject; bh=XUloMLRvD65MS8q2DriEUBZ9uHb1RahsmJYT7z5cG10=; b=owGbwMvMwCVmkMcZplerG8N4Wi2JIWtCZtTuOV5JlpnrJizO3SIa5RP/t4Tn/ifHNOsnDx+fP HTx0dWVHaUsDGJcDLJiiiwCs/++23l6olSt8yxZmDmsTCBDGLg4BWAi2+QYGXbGcpgrLuq5fD6X +2rW/cMbDn/8/pzb5/+S7cdf2hydNf0II8NPvaYrbJ+rDfaHVGrc4Nj9nsk1dV3NbkUZ/r+/KkR j77IDAA== X-Mailer: git-send-email 2.55.0.897.gb25b4bd76c-goog Message-ID: <20260827164409.3421848-6-ardb+git@google.com> Subject: [RFC PATCH v2 0/4] arm64: mm: Map fixmap page tables read-only From: Ard Biesheuvel To: linux-kernel@vger.kernel.org Cc: linux-arm-kernel@lists.infradead.org, Ard Biesheuvel , Ryan Roberts , Anshuman Khandual , Kevin Brodsky , Liz Prucka , Seth Jenkins , Kees Cook , Jann Horn , linux-hardening@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260827_094433_434324_A6106E5B X-CRM114-Status: GOOD ( 10.48 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org From: Ard Biesheuvel This v2 now covers intermediate level page tables as well as the PTE level page table for the fixmap. The latter is a special case, as it a) is only accessed via the kernel image's mapping, and never via the linear map (except for ptdump etc) b) must be accessible via a read-write mapping, as all manipulation of read-only page table descriptors relies on the fixmap itself and so it is treated separately. The intermediate page tables may be shared with other mappings in the upper kernel/vmalloc region, so they must be updatable using the ordinary APIs. Build tested and boot tested on a Lenovo Yoga C630 using 16k pages. v1: https://lore.kernel.org/all/20260805104042.1107678-2-ardb+git@google.com/ Cc: Ryan Roberts Cc: Anshuman Khandual Cc: Kevin Brodsky Cc: Liz Prucka Cc: Seth Jenkins Cc: Kees Cook Cc: Jann Horn Cc: linux-hardening@vger.kernel.org Ard Biesheuvel (4): arm64: mm: Map fixmap PTE tables r/o in the linear map arm64: mm: Use fault handler to permit swapper_pg_dir updates arm64: mm: Create r/o page table region that permits updates arm64: mm: Move fixmap intermediate page tables into .rodata arch/arm64/include/asm/fixmap.h | 4 ++ arch/arm64/include/asm/linkage.h | 1 + arch/arm64/include/asm/pgtable.h | 55 ++++++++------------ arch/arm64/kernel/vmlinux.lds.S | 6 +++ arch/arm64/mm/fixmap.c | 12 +++-- arch/arm64/mm/mmu.c | 48 +++++++++++++---- 6 files changed, 78 insertions(+), 48 deletions(-) -- 2.55.0.887.g758fc8c411-goog