Subject: Re: [PATCH 17/25] powerpc: helper to validate key-access permissions of a pte

From: Balbir Singh <[email-masked]>
Date: Wed, 18 Oct 2017 15:48:31 +1100

On Fri,  8 Sep 2017 15:45:05 -0700
Ram Pai <[email-masked]> wrote:

> helper function that checks if the read/write/execute is allowed
> on the pte.
> 
> Signed-off-by: Ram Pai <[email-masked]>
> ---
>  arch/powerpc/include/asm/book3s/64/pgtable.h |    4 +++
>  arch/powerpc/include/asm/pkeys.h             |   12 +++++++++++
>  arch/powerpc/mm/pkeys.c                      |   28 ++++++++++++++++++++++++++
>  3 files changed, 44 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
> index 5935d4e..bd244b3 100644
> --- a/arch/powerpc/include/asm/book3s/64/pgtable.h
> +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
> @@ -492,6 +492,10 @@ static inline void write_uamor(u64 value)
>  	mtspr(SPRN_UAMOR, value);
>  }
>  
> +#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
> +extern bool arch_pte_access_permitted(u64 pte, bool write, bool execute);
> +#endif /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
> +
>  #define __HAVE_ARCH_PTEP_GET_AND_CLEAR
>  static inline pte_t ptep_get_and_clear(struct mm_struct *mm,
>  				       unsigned long addr, pte_t *ptep)
> diff --git a/arch/powerpc/include/asm/pkeys.h b/arch/powerpc/include/asm/pkeys.h
> index cd3924c..50522a0 100644
> --- a/arch/powerpc/include/asm/pkeys.h
> +++ b/arch/powerpc/include/asm/pkeys.h
> @@ -80,6 +80,18 @@ static inline u64 pte_to_hpte_pkey_bits(u64 pteflags)
>  		((pteflags & H_PAGE_PKEY_BIT4) ? HPTE_R_KEY_BIT4 : 0x0UL));
>  }
>  
> +static inline u16 pte_to_pkey_bits(u64 pteflags)
> +{
> +	if (!pkey_inited)
> +		return 0x0UL;
> +
> +	return (((pteflags & H_PAGE_PKEY_BIT0) ? 0x10 : 0x0UL) |
> +		((pteflags & H_PAGE_PKEY_BIT1) ? 0x8 : 0x0UL) |
> +		((pteflags & H_PAGE_PKEY_BIT2) ? 0x4 : 0x0UL) |
> +		((pteflags & H_PAGE_PKEY_BIT3) ? 0x2 : 0x0UL) |
> +		((pteflags & H_PAGE_PKEY_BIT4) ? 0x1 : 0x0UL));
> +}
> +
>  #define ARCH_VM_PKEY_FLAGS (VM_PKEY_BIT0 | VM_PKEY_BIT1 | VM_PKEY_BIT2 | \
>  				VM_PKEY_BIT3 | VM_PKEY_BIT4)
>  #define AMR_BITS_PER_PKEY 2
> diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
> index fb1a76a..24589d9 100644
> --- a/arch/powerpc/mm/pkeys.c
> +++ b/arch/powerpc/mm/pkeys.c
> @@ -292,3 +292,31 @@ int __arch_override_mprotect_pkey(struct vm_area_struct *vma, int prot,
>  	 */
>  	return vma_pkey(vma);
>  }
> +
> +static bool pkey_access_permitted(int pkey, bool write, bool execute)
> +{
> +	int pkey_shift;
> +	u64 amr;
> +
> +	if (!pkey)
> +		return true;

Why would we have pkey set to 0, it's reserved. Why do we return true?

> +
> +	pkey_shift = pkeyshift(pkey);
> +	if (!(read_uamor() & (0x3UL << pkey_shift)))
> +		return true;
> +
> +	if (execute && !(read_iamr() & (IAMR_EX_BIT << pkey_shift)))
> +		return true;
> +
> +	amr = read_amr(); /* delay reading amr uptil absolutely needed*/
> +	return ((!write && !(amr & (AMR_RD_BIT << pkey_shift))) ||
> +		(write &&  !(amr & (AMR_WR_BIT << pkey_shift))));
> +}
> +
> +bool arch_pte_access_permitted(u64 pte, bool write, bool execute)
> +{
> +	if (!pkey_inited)
> +		return true;

Again, don't like the pkey_inited bits :)

> +	return pkey_access_permitted(pte_to_pkey_bits(pte),
> +			write, execute);
> +}

Balbir Singh