From bf25266f83821697dc5cc3571ff5e079840db027 Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel Date: Tue, 11 Mar 2025 08:30:44 +0100 Subject: [PATCH] arm64/kernel: Always use level 2 or higher for early mappings The page table population code in map_range() uses a recursive algorithm to create the early mappings of the kernel, the DTB and the ID mapped text and data pages, and this fails to take into account that the way these page tables may be constructed is not precisely the same at each level. In particular, block mappings are not permitted at each level, and the code as it exists today might inadvertently create such a forbidden block mapping if it were used to map a region of the appropriate size and alignment. This never happens in practice, given the limited size of the assets being mapped by the early boot code. Nonetheless, it would be better if this code would behave correctly in all circumstances. So only permit block mappings at level 2, and page mappings at level 3, for any page size, and use table mappings exclusively at all other levels. This change should have no impact in practice, but it makes the code more robust. Cc: Anshuman Khandual Reported-by: Ryan Roberts Signed-off-by: Ard Biesheuvel Reviewed-by: Anshuman Khandual Reviewed-by: Ryan Roberts Link: https://lore.kernel.org/r/20250311073043.96795-2-ardb+git@google.com Signed-off-by: Catalin Marinas --- arch/arm64/kernel/pi/map_range.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/arm64/kernel/pi/map_range.c b/arch/arm64/kernel/pi/map_range.c index 2b69e3beeef80..5778697f3062b 100644 --- a/arch/arm64/kernel/pi/map_range.c +++ b/arch/arm64/kernel/pi/map_range.c @@ -45,12 +45,12 @@ void __init map_range(u64 *pte, u64 start, u64 end, u64 pa, pgprot_t prot, * clearing the mapping */ if (protval) - protval |= (level < 3) ? PMD_TYPE_SECT : PTE_TYPE_PAGE; + protval |= (level == 2) ? PMD_TYPE_SECT : PTE_TYPE_PAGE; while (start < end) { u64 next = min((start | lmask) + 1, PAGE_ALIGN(end)); - if (level < 3 && (start | next | pa) & lmask) { + if (level < 2 || (level == 2 && (start | next | pa) & lmask)) { /* * This chunk needs a finer grained mapping. Create a * table mapping if necessary and recurse.