From fcf8dda8cc4860076395d807d9b3f781ca1d8f4f Mon Sep 17 00:00:00 2001 From: Dev Jain Date: Thu, 3 Apr 2025 10:58:44 +0530 Subject: [PATCH] arm64: pageattr: Explicitly bail out when changing permissions for vmalloc_huge mappings arm64 uses apply_to_page_range to change permissions for kernel vmalloc mappings, which does not support changing permissions for block mappings. This function will change permissions until it encounters a block mapping, and will bail out with a warning. Since there are no reports of this triggering, it implies that there are currently no cases of code doing a vmalloc_huge() followed by partial permission change. But this is a footgun waiting to go off, so let's detect it early and avoid the possibility of permissions in an intermediate state. So, explicitly disallow changing permissions for VM_ALLOW_HUGE_VMAP mappings. Reviewed-by: Ryan Roberts Reviewed-by: Mike Rapoport (Microsoft) Signed-off-by: Dev Jain Acked-by: David Hildenbrand Reviewed-by: Gavin Shan Reviewed-by: Anshuman Khandual Link: https://lore.kernel.org/r/20250403052844.61818-1-dev.jain@arm.com Signed-off-by: Will Deacon --- arch/arm64/mm/pageattr.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c index 39fd1f7ff02a..04d4a8f676db 100644 --- a/arch/arm64/mm/pageattr.c +++ b/arch/arm64/mm/pageattr.c @@ -96,8 +96,8 @@ static int change_memory_common(unsigned long addr, int numpages, * we are operating on does not result in such splitting. * * Let's restrict ourselves to mappings created by vmalloc (or vmap). - * Those are guaranteed to consist entirely of page mappings, and - * splitting is never needed. + * Disallow VM_ALLOW_HUGE_VMAP mappings to guarantee that only page + * mappings are updated and splitting is never needed. * * So check whether the [addr, addr + size) interval is entirely * covered by precisely one VM area that has the VM_ALLOC flag set. @@ -105,7 +105,7 @@ static int change_memory_common(unsigned long addr, int numpages, area = find_vm_area((void *)addr); if (!area || end > (unsigned long)kasan_reset_tag(area->addr) + area->size || - !(area->flags & VM_ALLOC)) + ((area->flags & (VM_ALLOC | VM_ALLOW_HUGE_VMAP)) != VM_ALLOC)) return -EINVAL; if (!numpages) -- 2.50.1