mlock in libc

[James A Morrison <ja2morri at student dot math dot uwaterloo dot ca>]

 Hi,

  I was looking at why gpg fails to build on the Hurd.  I discovered mlock
is what is broken.  The problem arises when the actual protection on the
memory is less relaxed than the protection passed to vm_wire.  What does work
is using VM_PROT_DEFAULT, because memory allocated with malloc seems to use
VM_PROT_DEFAULT.  However, I think the best solution is to call vm_region
and actually get the proper permissions for the pages.

 Here are a couple of patches that checks vm_region and acts more like 
wire_segment_internal in [hurd]/libshouldbeinlibc.  The first patch relaxes
the permissions on the memory region to max_protection so that the wired
region can have its protections relaxed to that level at any time.  The
second does not because perhaps something could write to a read-only part
of memory between the calls to vm_protect.

2002-11-03  James Morrison  <ja2morri@uwaterloo.ca>

	* sysdeps/mach/hurd/mlock.c (mlock): Get the actual protections on a
	region of memory before wiring it.

Index: mlock.c
===================================================================
RCS file: /cvs/glibc/libc/sysdeps/mach/hurd/mlock.c,v
retrieving revision 1.2
diff -u -r1.2 mlock.c
--- mlock.c     6 Jul 2001 04:55:57 -0000       1.2
+++ mlock.c     3 Nov 2002 16:18:09 -0000
@@ -39,8 +39,19 @@

   page = trunc_page ((vm_address_t) addr);
   len = round_page ((vm_address_t) addr + len) - page;
-  err = __vm_wire (hostpriv, __mach_task_self (), page, len,
-                  VM_PROT_ALL); /* XXX ? */
+  {
+    vm_prot_t cur, max;
+    vm_inherit_t inher;
+    boolean_t shared;
+    mach_port_t obj;
+    vm_offset_t offs;
+
+    __vm_region (mach_task_self (), &page, &len, &cur, &max, &inher, &shared,
+               &obj, &offs);
+    __vm_protect (mach_task_self (), page, len, 0, max);
+    err = __vm_wire (hostpriv, __mach_task_self (), page, len, max);
+    __vm_protect (mach_task_self (), page, len, 0, cur);
+  }
   __mach_port_deallocate (__mach_task_self (), hostpriv);

   return err ? __hurd_fail (err) : 0;

Index: mlock.c
===================================================================
RCS file: /cvs/glibc/libc/sysdeps/mach/hurd/mlock.c,v
retrieving revision 1.2
diff -u -r1.2 mlock.c
--- mlock.c     6 Jul 2001 04:55:57 -0000       1.2
+++ mlock.c     3 Nov 2002 16:25:44 -0000
@@ -39,8 +39,18 @@

   page = trunc_page ((vm_address_t) addr);
   len = round_page ((vm_address_t) addr + len) - page;
-  err = __vm_wire (hostpriv, __mach_task_self (), page, len,
-                  VM_PROT_ALL); /* XXX ? */
+  {
+    vm_prot_t cur, max;
+    vm_inherit_t inher;
+    boolean_t shared;
+    mach_port_t obj;
+    vm_offset_t offs;
+
+    __vm_region (mach_task_self (), &page, &len, &cur, &max, &inher, &shared,
+               &obj, &offs);
+    err = __vm_wire (hostpriv, __mach_task_self (), page, len, max);
+    __mach_port_deallocate (mach_task_self (), obj);
+  }
   __mach_port_deallocate (__mach_task_self (), hostpriv);

   return err ? __hurd_fail (err) : 0;