Re: [PATCH v2] arm64: pageattr: Explicitly bail out when changing permissions for vmalloc_huge mappings

[Gavin Shan]

On 4/3/25 3:28 PM, Dev Jain wrote:
> 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@xxxxxxx>
> Reviewed-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
> Signed-off-by: Dev Jain <dev.jain@xxxxxxx>
> ---
> v1->v2:
>   - Improve changelog, keep mention of page mappings in comment
>
>   arch/arm64/mm/pageattr.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)

Reviewed-by: Gavin Shan <gshan@xxxxxxxxxx>