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Mon, 27 Apr 2026 08:35:47 -0700 (PDT) Date: Mon, 27 Apr 2026 17:34:29 +0200 In-Reply-To: <20260427153416.2103979-17-ardb+git@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260427153416.2103979-17-ardb+git@google.com> X-Developer-Key: i=ardb@kernel.org; a=openpgp; fpr=F43D03328115A198C90016883D200E9CA6329909 X-Developer-Signature: v=1; a=openpgp-sha256; l=3111; i=ardb@kernel.org; h=from:subject; bh=vnOPgzR9gwGy7RU3jbNwlQgfBXncMvaaP3oMs7gg07Y=; b=owGbwMvMwCVmkMcZplerG8N4Wi2JIfN9E7fhjbPcgs4XVKfeTnOd6X5d81L1wd6JdtmfgucZt Dn6GzB2lLIwiHExyIopsgjM/vtu5+mJUrXOs2Rh5rAygQxh4OIUgIlM/Mfwz1hYf8184+dKqf8u huwKYeCbfkN1Q8PZ5+f9Qlm8AtrWXmX4Z3804IBu667aItk0A8Wfbn81/Y/98HK+tuNd4pHLyrc 5WQA= X-Mailer: git-send-email 2.54.0.rc2.544.gc7ae2d5bb8-goog Message-ID: <20260427153416.2103979-29-ardb+git@google.com> Subject: [PATCH v4 12/15] arm64: mm: Map the kernel data/bss read-only in the linear map From: Ard Biesheuvel To: 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 Content-Type: text/plain; charset="UTF-8" From: Ard Biesheuvel On systems where the bootloader adheres to the original arm64 boot protocol, the placement of the kernel in the physical address space is highly predictable, and this makes the placement of its linear alias in the kernel virtual address space equally predictable, given the lack of randomization of the linear map. The linear aliases of the kernel text and rodata regions are already mapped read-only, but the kernel data and bss are mapped read-write in this region. This is not needed, so map them read-only as well. Note that the statically allocated kernel page tables do need to be modifiable via the linear map, so leave these mapped read-write. Signed-off-by: Ard Biesheuvel --- arch/arm64/include/asm/sections.h | 1 + arch/arm64/mm/mmu.c | 16 ++++++++++++++-- 2 files changed, 15 insertions(+), 2 deletions(-) diff --git a/arch/arm64/include/asm/sections.h b/arch/arm64/include/asm/sections.h index 51b0d594239e..32ec21af0823 100644 --- a/arch/arm64/include/asm/sections.h +++ b/arch/arm64/include/asm/sections.h @@ -23,6 +23,7 @@ extern char __irqentry_text_start[], __irqentry_text_end[]; extern char __mmuoff_data_start[], __mmuoff_data_end[]; extern char __entry_tramp_text_start[], __entry_tramp_text_end[]; extern char __relocate_new_kernel_start[], __relocate_new_kernel_end[]; +extern char __fixmap_pgdir_start[]; static inline size_t entry_tramp_text_size(void) { diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index 1a4b4337d29a..9361b7efb848 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -1122,7 +1122,9 @@ static void __init map_mem(void) { static const u64 direct_map_end = _PAGE_END(VA_BITS_MIN); phys_addr_t kernel_start = __pa_symbol(_text); - phys_addr_t kernel_end = __pa_symbol(__init_begin); + phys_addr_t init_begin = __pa_symbol(__init_begin); + phys_addr_t init_end = __pa_symbol(__init_end); + phys_addr_t kernel_end = __pa_symbol(__fixmap_pgdir_start); phys_addr_t start, end; int flags = NO_EXEC_MAPPINGS; u64 i; @@ -1155,7 +1157,11 @@ static void __init map_mem(void) * of the region accessible to subsystems such as hibernate, * but protects it from inadvertent modification or execution. */ - __map_memblock(kernel_start, kernel_end, pgprot_tagged(PAGE_KERNEL), + __map_memblock(kernel_start, init_begin, pgprot_tagged(PAGE_KERNEL), + flags); + + /* Map the kernel data/bss so it can be remapped later */ + __map_memblock(init_end, kernel_end, pgprot_tagged(PAGE_KERNEL), flags); /* map all the memory banks */ @@ -1168,6 +1174,12 @@ static void __init map_mem(void) __map_memblock(start, end, pgprot_tagged(PAGE_KERNEL), flags); } + + /* Map the kernel data/bss read-only in the linear map */ + __map_memblock(init_end, kernel_end, pgprot_tagged(PAGE_KERNEL_RO), + flags); + flush_tlb_kernel_range((unsigned long)lm_alias(__init_end), + (unsigned long)lm_alias(__fixmap_pgdir_start)); } void mark_rodata_ro(void) -- 2.54.0.rc2.544.gc7ae2d5bb8-goog