Subject: Re: [patch 1/6] mm: Allow architectures to define additional protection bits

From: Andrew Morton <[email-masked]>
Date: Tue, 1 Jul 2008 01:53:01 -0700

On Wed, 18 Jun 2008 17:32:55 -0500 [email-masked] wrote:

> This patch allows architectures to define functions to deal with
> additional protections bits for mmap() and mprotect().
> 
> arch_calc_vm_prot_bits() maps additonal protection bits to vm_flags
> arch_vm_get_page_prot() maps additional vm_flags to the vma's vm_page_prot
> arch_validate_prot() checks for valid values of the protection bits

It'd be simpler if Paul were to merge this.  It doesn't conflict with
any pending work.

Acked-by: Andrew Morton <[email-masked]>

> Note: vm_get_page_prot() is now pretty ugly.

It is.  But afacit it generates the same code for non-powerpc.

> Suggestions?

nfi.  Let us rub the Hugh-summoning lamp.

> Signed-off-by: Dave Kleikamp <[email-masked]>
> ---
> 
>  include/linux/mman.h |   28 +++++++++++++++++++++++++++-
>  mm/mmap.c            |    5 +++--
>  mm/mprotect.c        |    2 +-
>  3 files changed, 31 insertions(+), 4 deletions(-)
> 
> Index: linux-2.6.26-rc5/include/linux/mman.h
> ===================================================================
> --- linux-2.6.26-rc5.orig/include/linux/mman.h
> +++ linux-2.6.26-rc5/include/linux/mman.h
> @@ -34,6 +34,31 @@ static inline void vm_unacct_memory(long
>  }
>  
>  /*
> + * Allow architectures to handle additional protection bits
> + */
> +
> +#ifndef arch_calc_vm_prot_bits
> +#define arch_calc_vm_prot_bits(prot) 0
> +#endif
> +
> +#ifndef arch_vm_get_page_prot
> +#define arch_vm_get_page_prot(vm_flags) __pgprot(0)
> +#endif
> +
> +#ifndef arch_validate_prot
> +/*
> + * This is called from mprotect().  PROT_GROWSDOWN and PROT_GROWSUP have
> + * already been masked out.
> + *
> + * Returns true if the prot flags are valid
> + */
> +static inline int arch_validate_prot(unsigned long prot)
> +{
> +	return (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM)) == 0;
> +}

Officially we should now have

#define arch_validate_prot arch_validate_prot

here.

> +#endif
> +
> +/*
>   * Optimisation macro.  It is equivalent to:
>   *      (x & bit1) ? bit2 : 0
>   * but this version is faster.
> @@ -51,7 +76,8 @@ calc_vm_prot_bits(unsigned long prot)
>  {
>  	return _calc_vm_trans(prot, PROT_READ,  VM_READ ) |
>  	       _calc_vm_trans(prot, PROT_WRITE, VM_WRITE) |
> -	       _calc_vm_trans(prot, PROT_EXEC,  VM_EXEC );
> +	       _calc_vm_trans(prot, PROT_EXEC,  VM_EXEC) |
> +	       arch_calc_vm_prot_bits(prot);
>  }
>  
>  /*
> Index: linux-2.6.26-rc5/mm/mmap.c
> ===================================================================
> --- linux-2.6.26-rc5.orig/mm/mmap.c
> +++ linux-2.6.26-rc5/mm/mmap.c
> @@ -72,8 +72,9 @@ pgprot_t protection_map[16] = {
>  
>  pgprot_t vm_get_page_prot(unsigned long vm_flags)
>  {
> -	return protection_map[vm_flags &
> -				(VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)];
> +	return __pgprot(pgprot_val(protection_map[vm_flags &
> +				(VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]) |
> +			pgprot_val(arch_vm_get_page_prot(vm_flags)));
>  }
>  EXPORT_SYMBOL(vm_get_page_prot);
>  
> Index: linux-2.6.26-rc5/mm/mprotect.c
> ===================================================================
> --- linux-2.6.26-rc5.orig/mm/mprotect.c
> +++ linux-2.6.26-rc5/mm/mprotect.c
> @@ -239,7 +239,7 @@ sys_mprotect(unsigned long start, size_t
>  	end = start + len;
>  	if (end <= start)
>  		return -ENOMEM;
> -	if (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM))
> +	if (!arch_validate_prot(prot))
>  		return -EINVAL;
>  
>  	reqprot = prot;
> 
> --