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

Dave Kleikamp
2008-07-01T13:54:59Z

On Tue, 2008-07-01 at 01:53 -0700, Andrew Morton wrote:
> On Wed, 18 Jun 2008 17:32:55 -0500 shaggy@linux.vnet.ibm.com 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.

That works for me. Paul, I'll send you an updated patchset.

> Acked-by: Andrew Morton <akpm@linux-foundation.org>
>
> > 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 <shaggy@linux.vnet.ibm.com>
> > ---
> >
> > 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.

No problem.

> > +#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;
> >
> > --
--
David Kleikamp
IBM Linux Technology Center