[RFC 09/12] mm: Restrict memory encryption to anonymous VMA's

[Sakkinen, Jarkko]

On Fri, 2018-09-07 at 15:37 -0700, Alison Schofield wrote:
> Memory encryption is only supported for mappings that are ANONYMOUS.
> Test the entire range of VMA's in an encrypt_mprotect() request to
> make sure they all meet that requirement before encrypting any.
> 
> The encrypt_mprotect syscall will return -EINVAL and will not encrypt
> any VMA's if this check fails.
> 
> Signed-off-by: Alison Schofield <alison.schofield at intel.com>
> ---
>  mm/mprotect.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/mm/mprotect.c b/mm/mprotect.c
> index 6c2e1106525c..3384b755aad1 100644
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -311,6 +311,24 @@ unsigned long change_protection(struct vm_area_struct
> *vma, unsigned long start,
>  	return pages;
>  }
>  
> +/*
> + * Encrypted mprotect is only supported on anonymous mappings.
> + * All VMA's in the requested range must be anonymous. If this
> + * test fails on any single VMA, the entire mprotect request fails.
> + */

kdoc

> +bool mem_supports_encryption(struct vm_area_struct *vma, unsigned long end)
> +{
> +	struct vm_area_struct *test_vma = vma;
> +
> +	do {
> +		if (!vma_is_anonymous(test_vma))
> +			return false;
> +
> +		test_vma = test_vma->vm_next;
> +	} while (test_vma && test_vma->vm_start < end);
> +	return true;
> +}
> +
>  int
>  mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
>  	       unsigned long start, unsigned long end, unsigned long
> newflags,
> @@ -491,6 +509,10 @@ static int do_mprotect_ext(unsigned long start, size_t
> len,
>  				goto out;
>  		}
>  	}
> +	if (keyid > 0 && !mem_supports_encryption(vma, end)) {
> +		error = -EINVAL;
> +		goto out;
> +	}
>  	if (start > vma->vm_start)
>  		prev = vma;
>  

/Jarkko