Re: [PATCH V3] arm64/mm: Validate hotplug range before creating linear mapping

[Ard Biesheuvel]

On Fri, 13 Nov 2020 at 08:31, Anshuman Khandual
<anshuman.khandual@xxxxxxx> wrote:
>
> During memory hotplug process, the linear mapping should not be created for
> a given memory range if that would fall outside the maximum allowed linear
> range. Else it might cause memory corruption in the kernel virtual space.
>
> Maximum linear mapping region is [PAGE_OFFSET..(PAGE_END -1)] accommodating
> both its ends but excluding PAGE_END. Max physical range that can be mapped
> inside this linear mapping range, must also be derived from its end points.
>
> This ensures that arch_add_memory() validates memory hot add range for its
> potential linear mapping requirements, before creating it with
> __create_pgd_mapping().
>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Ard Biesheuvel <ardb@xxxxxxxxxx>
> Cc: Steven Price <steven.price@xxxxxxx>
> Cc: Robin Murphy <robin.murphy@xxxxxxx>
> Cc: David Hildenbrand <david@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Fixes: 4ab215061554 ("arm64: Add memory hotplug support")
> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> ---
> This applies on 5.10-rc3
>
> Changes in V3:
>
> - Dropped comment paragraphs from code and commit message per Ard
> - Dropped parenthesis brackets in the comparison per Ard
>
> Changes in V2: (https://lore.kernel.org/linux-arm-kernel/1605236574-14636-1-git-send-email-anshuman.khandual@xxxxxxx/)
>
> - Replaced (start + size) with (start + size - 1) in the comparison per Ard
> - Dropped parenthesis brackets in the comparison per Ard
>
> Changes in V1: (https://lore.kernel.org/linux-arm-kernel/1600332402-30123-1-git-send-email-anshuman.khandual@xxxxxxx/)
>
>  arch/arm64/mm/mmu.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
>
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 1c0f3e02f731..ca692a815731 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1444,11 +1444,28 @@ static void __remove_pgd_mapping(pgd_t *pgdir, unsigned long start, u64 size)
>         free_empty_tables(start, end, PAGE_OFFSET, PAGE_END);
>  }
>
> +static bool inside_linear_region(u64 start, u64 size)
> +{
> +       /*
> +        * Linear mapping region is the range [PAGE_OFFSET..(PAGE_END - 1)]
> +        * accommodating both its ends but excluding PAGE_END. Max physical
> +        * range which can be mapped inside this linear mapping range, must
> +        * also be derived from its end points.
> +        */
> +       return start >= __pa(_PAGE_OFFSET(vabits_actual)) &&
> +              (start + size - 1) <= __pa(PAGE_END - 1);
> +}
> +
>  int arch_add_memory(int nid, u64 start, u64 size,
>                     struct mhp_params *params)
>  {
>         int ret, flags = 0;
>
> +       if (!inside_linear_region(start, size)) {
> +               pr_err("[%llx %llx] is outside linear mapping region\n", start, start + size);
> +               return -EINVAL;
> +       }
> +
>         if (rodata_full || debug_pagealloc_enabled())
>                 flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
>

Reviewed-by: Ard Biesheuvel <ardb@xxxxxxxxxx>