Re: [PATCH] cma: fail if fixed declaration can't be honored

["Michał Nazarewicz" <mina86@mina86.com>]

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On Tue, 25 Jun 2019 at 01:22, Doug Berger <opendmb@gmail.com> wrote:

> The description of the cma_declare_contiguous() function indicates
> that if the 'fixed' argument is true the reserved contiguous area
> must be exactly at the address of the 'base' argument.
>
> However, the function currently allows the 'base', 'size', and
> 'limit' arguments to be silently adjusted to meet alignment
> constraints. This commit enforces the documented behavior through
> explicit checks that return an error if the region does not fit
> within a specified region.
>
> Fixes: 5ea3b1b2f8ad ("cma: add placement specifier for "cma=" kernel
> parameter")
> Signed-off-by: Doug Berger <opendmb@gmail.com>
>

Acked-by: Michal Nazarewicz <mina86@mina86.com>


> ---
>  mm/cma.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
>
> diff --git a/mm/cma.c b/mm/cma.c
> index 3340ef34c154..4973d253dc83 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -278,6 +278,12 @@ int __init cma_declare_contiguous(phys_addr_t base,
>          */
>         alignment = max(alignment,  (phys_addr_t)PAGE_SIZE <<
>                           max_t(unsigned long, MAX_ORDER - 1,
> pageblock_order));
> +       if (fixed && base & (alignment - 1)) {
> +               ret = -EINVAL;
> +               pr_err("Region at %pa must be aligned to %pa bytes\n",
> +                       &base, &alignment);
> +               goto err;
> +       }
>
        base = ALIGN(base, alignment);
>         size = ALIGN(size, alignment);
>         limit &= ~(alignment - 1);
> @@ -308,6 +314,13 @@ int __init cma_declare_contiguous(phys_addr_t base,
>         if (limit == 0 || limit > memblock_end)
>                 limit = memblock_end;
>
> +       if (base + size > limit) {
> +               ret = -EINVAL;
> +               pr_err("Size (%pa) of region at %pa exceeds limit (%pa)\n",
> +                       &size, &base, &limit);
> +               goto err;
> +       }
> +
>         /* Reserve memory */
>         if (fixed) {
>                 if (memblock_is_region_reserved(base, size) ||
> --
> 2.7.4
>
>

-- 
Best regards
ミハウ “𝓶𝓲𝓷𝓪86” ナザレヴイツ
«If at first you don’t succeed, give up skydiving»

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