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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 <ryan.roberts@arm.com>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Dev Jain <dev.jain@arm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Link: https://lore.kernel.org/r/20250403052844.61818-1-dev.jain@arm.com
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Dev Jain 2025-04-03 10:58:44 +05:30 committed by Will Deacon
parent f101c56447
commit fcf8dda8cc
1 changed files with 3 additions and 3 deletions
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6
arch/arm64/mm/pageattr.c
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@ -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)