linux-kernel - [PATCH v2 08/10] arm64: mm: Don't abuse memblock NOMAP to check for overlaps

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Message-ID: <20260126092630.1800589-20-ardb+git@google.com>
Date: Mon, 26 Jan 2026 10:26:39 +0100
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: linux-arm-kernel@...ts.infradead.org, will@...nel.org, 
	catalin.marinas@....com, mark.rutland@....com, 
	Ard Biesheuvel <ardb@...nel.org>, Ryan Roberts <ryan.roberts@....com>, 
	Anshuman Khandual <anshuman.khandual@....com>, Liz Prucka <lizprucka@...gle.com>, 
	Seth Jenkins <sethjenkins@...gle.com>, Kees Cook <kees@...nel.org>, 
	linux-hardening@...r.kernel.org
Subject: [PATCH v2 08/10] arm64: mm: Don't abuse memblock NOMAP to check for overlaps

From: Ard Biesheuvel <ardb@...nel.org>

Now that the DRAM mapping routines respect existing table mappings and
contiguous block and page mappings, it is no longer needed to fiddle
with the memblock tables to set and clear the NOMAP attribute. Instead,
map the kernel text and rodata alias first, avoiding contiguous
mappings, so that they will not be added later when mapping the
memblocks.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/arm64/mm/mmu.c | 27 ++++++++------------
 1 file changed, 10 insertions(+), 17 deletions(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 80587cd47ce7..18415d4743bf 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1149,12 +1149,17 @@ static void __init map_mem(void)
 		flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
 
 	/*
-	 * Take care not to create a writable alias for the
-	 * read-only text and rodata sections of the kernel image.
-	 * So temporarily mark them as NOMAP to skip mappings in
-	 * the following for-loop
+	 * Map the linear alias of the [_text, __init_begin) interval
+	 * as non-executable now, and remove the write permission in
+	 * mark_linear_text_alias_ro() above (which will be called after
+	 * alternative patching has completed). This makes the contents
+	 * of the region accessible to subsystems such as hibernate,
+	 * but protects it from inadvertent modification or execution.
+	 * Note that contiguous mappings cannot be remapped in this way,
+	 * so we should avoid them here.
 	 */
-	memblock_mark_nomap(kernel_start, kernel_end - kernel_start);
+	__map_memblock(kernel_start, kernel_end, PAGE_KERNEL,
+		       flags | NO_CONT_MAPPINGS);
 
 	/* map all the memory banks */
 	for_each_mem_range(i, &start, &end) {
@@ -1167,18 +1172,6 @@ static void __init map_mem(void)
 			       flags);
 	}
 
-	/*
-	 * Map the linear alias of the [_text, __init_begin) interval
-	 * as non-executable now, and remove the write permission in
-	 * mark_linear_text_alias_ro() below (which will be called after
-	 * alternative patching has completed). This makes the contents
-	 * of the region accessible to subsystems such as hibernate,
-	 * but protects it from inadvertent modification or execution.
-	 * Note that contiguous mappings cannot be remapped in this way,
-	 * so we should avoid them here.
-	 */
-	__map_memblock(kernel_start, kernel_end, PAGE_KERNEL, NO_CONT_MAPPINGS);
-	memblock_clear_nomap(kernel_start, kernel_end - kernel_start);
 	arm64_kfence_map_pool(early_kfence_pool);
 }
 
-- 
2.52.0.457.g6b5491de43-goog