Subject: Re: [PATCH 19/25] powerpc: implementation for arch_vma_access_permitted()

From: Balbir Singh <[email-masked]>
Date: Thu, 19 Oct 2017 10:20:46 +1100

On Fri,  8 Sep 2017 15:45:07 -0700
Ram Pai <[email-masked]> wrote:

> This patch provides the implementation for
> arch_vma_access_permitted(). Returns true if the
> requested access is allowed by pkey associated with the
> vma.
> 
> Signed-off-by: Ram Pai <[email-masked]>
> ---
>  arch/powerpc/include/asm/mmu_context.h |    5 +++-
>  arch/powerpc/mm/pkeys.c                |   43 ++++++++++++++++++++++++++++++++
>  2 files changed, 47 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
> index 04e9221..9a56355 100644
> --- a/arch/powerpc/include/asm/mmu_context.h
> +++ b/arch/powerpc/include/asm/mmu_context.h
> @@ -135,6 +135,10 @@ static inline void arch_bprm_mm_init(struct mm_struct *mm,
>  {
>  }
>  
> +#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
> +bool arch_vma_access_permitted(struct vm_area_struct *vma,
> +			bool write, bool execute, bool foreign);
> +#else /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
>  static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,
>  		bool write, bool execute, bool foreign)
>  {
> @@ -142,7 +146,6 @@ static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,
>  	return true;
>  }
>  
> -#ifndef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
>  #define pkey_initialize()
>  #define pkey_mm_init(mm)
>  
> diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
> index 24589d9..21c3b42 100644
> --- a/arch/powerpc/mm/pkeys.c
> +++ b/arch/powerpc/mm/pkeys.c
> @@ -320,3 +320,46 @@ bool arch_pte_access_permitted(u64 pte, bool write, bool execute)
>  	return pkey_access_permitted(pte_to_pkey_bits(pte),
>  			write, execute);
>  }
> +
> +/*
> + * We only want to enforce protection keys on the current process
> + * because we effectively have no access to AMR/IAMR for other
> + * processes or any way to tell *which * AMR/IAMR in a threaded
> + * process we could use.
> + *
> + * So do not enforce things if the VMA is not from the current
> + * mm, or if we are in a kernel thread.
> + */
> +static inline bool vma_is_foreign(struct vm_area_struct *vma)
> +{
> +	if (!current->mm)
> +		return true;
> +	/*
> +	 * if the VMA is from another process, then AMR/IAMR has no
> +	 * relevance and should not be enforced.
> +	 */
> +	if (current->mm != vma->vm_mm)
> +		return true;
> +
> +	return false;
> +}
> +
> +bool arch_vma_access_permitted(struct vm_area_struct *vma,
> +		bool write, bool execute, bool foreign)
> +{
> +	int pkey;
> +
> +	if (!pkey_inited)
> +		return true;
> +
> +	/* allow access if the VMA is not one from this process */
> +	if (foreign || vma_is_foreign(vma))
> +		return true;
> +
> +	pkey = vma_pkey(vma);
> +
> +	if (!pkey)
> +		return true;
> +
> +	return pkey_access_permitted(pkey, write, execute);
> +}

Again, I think this is GUP, I don't really understand the top level
use case of enforcing permissions for GUP in a thread context.

Balbir Singh.