Commit fcf8dda8 authored by Dev Jain's avatar Dev Jain Committed by Will Deacon
Browse files

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: default avatarRyan Roberts <ryan.roberts@arm.com>
Reviewed-by: default avatarMike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: default avatarDev Jain <dev.jain@arm.com>
Acked-by: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarGavin Shan <gshan@redhat.com>
Reviewed-by: default avatarAnshuman Khandual <anshuman.khandual@arm.com>
Link: https://lore.kernel.org/r/20250403052844.61818-1-dev.jain@arm.com


Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent f101c564

arch/arm64/mm/pageattr.c

+3 −3
Original line number Diff line number Diff line
@@ -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)