From 7ace06a01efaba1ec585630aa4c98ac39b38452a Mon Sep 17 00:00:00 2001 From: liulhong617 Date: Wed, 13 May 2026 09:02:55 +0800 Subject: [PATCH] arm64: mm: fix accidental linear mapping of no-map reserved memory MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When reserved-memory regions with the "no-map" property are not page-aligned, the kernel may accidentally map them into the linear mapping, contradicting the no-map semantics. The root cause is a mismatch between /proc/iomem's address boundaries and the actual page table mapping boundaries: 1. /proc/iomem derives its ranges from memblock via memblock_region_reserved_base_pfn/memblock_region_reserved_end_pfn, which perform PFN rounding so the displayed boundaries are page-aligned. This gives the impression that the no-map region occupies whole pages. 2. However, memblock_mark_nomap() splits memblock.memory regions at exact byte boundaries (memblock_isolate_range preserves raw DT base/size with no alignment). When for_each_mem_range iterates the non-NOMAP regions adjacent to a no-map region, it returns start/end values that are NOT page-aligned — they are the precise byte boundaries from the memblock split. 3. These sub-page-aligned values are passed to __create_pgd_mapping_locked(), which does: phys &= PAGE_MASK; addr = virt & PAGE_MASK; end = PAGE_ALIGN(virt + size); The downward rounding of phys via PAGE_MASK extends the mapped range backward into the adjacent no-map region, effectively including no-map memory in the linear mapping. For example, with 64K pages, reserved_region@A2000000 (base=0xA2000000, size=0x8000, no-map) causes for_each_mem_range to return start=0xA2008000 for the next mappable region. After phys &= PAGE_MASK, the actual mapping starts at 0xA2000000 — the entire no-map region is incorrectly mapped. Fix this by rounding the mappable range inward to PAGE_SIZE boundaries before passing it to __map_memblock: start is rounded UP and end is rounded DOWN. This ensures the mapped area never overlaps with adjacent no-map regions. The cost is at most one page of unmapped gap at each boundary, which is preferable to violating no-map semantics. Signed-off-by: liulhong617 Signed-off-by: Will Deacon --- arch/arm64/mm/mmu.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index a25d8beacc83..f51566316ba4 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -1190,6 +1190,20 @@ static void __init map_mem(void) /* map all the memory banks */ for_each_mem_range(i, &start, &end) { + /* + * for_each_mem_range may return sub-page-aligned boundaries + * after memblock_mark_nomap() splits regions at byte precision. + * __create_pgd_mapping_locked aligns phys down to PAGE_MASK, + * which could accidentally map no-map memory on the boundary. + * Round the mappable range inward: start UP, end DOWN, so + * that the mapped area never overlaps with adjacent no-map + * regions. The cost is at most one page of unmapped gap at + * each boundary. + */ + start = PAGE_ALIGN(start); + end = end & PAGE_MASK; + if (start >= end) + continue; /* * The linear map must allow allocation tags reading/writing * if MTE is present. Otherwise, it has the same attributes as