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

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:

quoted

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>

quoted

Note: vm_get_page_prot() is now pretty ugly.

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

quoted

Suggestions?

nfi.  Let us rub the Hugh-summoning lamp.

quoted

Signed-off-by: Dave Kleikamp <redacted>
---

 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.

quoted

+#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