[PATCH 13/25] powerpc: implementation for arch_override_mprotect_pkey()

[Balbir Singh]

On Fri,  8 Sep 2017 15:45:01 -0700
Ram Pai <linuxram at us.ibm.com> wrote:

> arch independent code calls arch_override_mprotect_pkey()
> to return a pkey that best matches the requested protection.
> 
> This patch provides the implementation.
> 
> Signed-off-by: Ram Pai <linuxram at us.ibm.com>
> ---
>  arch/powerpc/include/asm/mmu_context.h |    5 +++
>  arch/powerpc/include/asm/pkeys.h       |   17 ++++++++++-
>  arch/powerpc/mm/pkeys.c                |   47 ++++++++++++++++++++++++++++++++
>  3 files changed, 67 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
> index c705a5d..8e5a87e 100644
> --- a/arch/powerpc/include/asm/mmu_context.h
> +++ b/arch/powerpc/include/asm/mmu_context.h
> @@ -145,6 +145,11 @@ static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,
>  #ifndef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
>  #define pkey_initialize()
>  #define pkey_mm_init(mm)
> +
> +static inline int vma_pkey(struct vm_area_struct *vma)
> +{
> +	return 0;
> +}
>  #endif /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
>  
>  #endif /* __KERNEL__ */
> diff --git a/arch/powerpc/include/asm/pkeys.h b/arch/powerpc/include/asm/pkeys.h
> index f13e913..d2fffef 100644
> --- a/arch/powerpc/include/asm/pkeys.h
> +++ b/arch/powerpc/include/asm/pkeys.h
> @@ -41,6 +41,16 @@ static inline u64 pkey_to_vmflag_bits(u16 pkey)
>  		((pkey & 0x10UL) ? VM_PKEY_BIT4 : 0x0UL));
>  }
>  
> +#define ARCH_VM_PKEY_FLAGS (VM_PKEY_BIT0 | VM_PKEY_BIT1 | VM_PKEY_BIT2 | \
> +				VM_PKEY_BIT3 | VM_PKEY_BIT4)
> +
> +static inline int vma_pkey(struct vm_area_struct *vma)
> +{
> +	if (!pkey_inited)
> +		return 0;

We don't want pkey_inited to be present in all functions, why do we need
a conditional branch for all functions. Even if we do, it should be a jump
label. I would rather we just removed !pkey_inited unless really really
required.

> +	return (vma->vm_flags & ARCH_VM_PKEY_FLAGS) >> VM_PKEY_SHIFT;
> +}
> +
>  #define arch_max_pkey()  pkeys_total
>  #define AMR_RD_BIT 0x1UL
>  #define AMR_WR_BIT 0x2UL
> @@ -142,11 +152,14 @@ static inline int execute_only_pkey(struct mm_struct *mm)
>  	return __execute_only_pkey(mm);
>  }
>  
> -
> +extern int __arch_override_mprotect_pkey(struct vm_area_struct *vma,
> +		int prot, int pkey);
>  static inline int arch_override_mprotect_pkey(struct vm_area_struct *vma,
>  		int prot, int pkey)
>  {
> -	return 0;
> +	if (!pkey_inited)
> +		return 0;
> +	return __arch_override_mprotect_pkey(vma, prot, pkey);
>  }
>  
>  extern int __arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
> diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
> index 8a24983..fb1a76a 100644
> --- a/arch/powerpc/mm/pkeys.c
> +++ b/arch/powerpc/mm/pkeys.c
> @@ -245,3 +245,50 @@ int __execute_only_pkey(struct mm_struct *mm)
>  		mm->context.execute_only_pkey = execute_only_pkey;
>  	return execute_only_pkey;
>  }
> +
> +static inline bool vma_is_pkey_exec_only(struct vm_area_struct *vma)
> +{
> +	/* Do this check first since the vm_flags should be hot */
> +	if ((vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC)) != VM_EXEC)
> +		return false;
> +
> +	return (vma_pkey(vma) == vma->vm_mm->context.execute_only_pkey);
> +}
> +
> +/*
> + * This should only be called for *plain* mprotect calls.

What's a plain mprotect call?

> + */
> +int __arch_override_mprotect_pkey(struct vm_area_struct *vma, int prot,
> +		int pkey)
> +{
> +	/*
> +	 * Is this an mprotect_pkey() call?  If so, never
> +	 * override the value that came from the user.
> +	 */
> +	if (pkey != -1)
> +		return pkey;

If the user specified a key, we always use it? Presumably the user
got it from pkey_alloc(), in other cases, the user was lazy and used
-1 in the mprotect call?

> +
> +	/*
> +	 * If the currently associated pkey is execute-only,
> +	 * but the requested protection requires read or write,
> +	 * move it back to the default pkey.
> +	 */
> +	if (vma_is_pkey_exec_only(vma) &&
> +	    (prot & (PROT_READ|PROT_WRITE)))
> +		return 0;
> +
> +	/*
> +	 * the requested protection is execute-only. Hence
> +	 * lets use a execute-only pkey.
> +	 */
> +	if (prot == PROT_EXEC) {
> +		pkey = execute_only_pkey(vma->vm_mm);
> +		if (pkey > 0)
> +			return pkey;
> +	}
> +
> +	/*
> +	 * nothing to override.
> +	 */
> +	return vma_pkey(vma);
> +}

Balbir Singh.