Code review comments from pmooney (sundry), and igork (screwups in zonecfg refactoring)
7029 want per-process exploit mitigation features (secflags)
7030 want basic address space layout randomization (aslr)
7031 noexec_user_stack should be a secflag
7032 want a means to forbid mappings around NULL.

*** 44,53 ****
--- 44,54 ----
  #include <sys/archsystm.h>
  #include <vm/hat_sfmmu.h>
  #include <sys/memnode.h>
  #include <sys/mem_cage.h>
  #include <vm/vm_dep.h>
+ #include <sys/random.h>
  
  #if defined(__sparcv9) && defined(SF_ERRATA_57)
  caddr_t errata57_limit;
  #endif
  
*** 135,144 ****
--- 136,152 ----
                  max_shm_lpsize = ismpagesize;
          }
  }
  
  /*
+  * The maximum amount a randomized mapping will be slewed.  We should perhaps
+  * arrange things so these tunables can be separate for mmap, mmapobj, and
+  * ld.so
+  */
+ size_t aslr_max_map_skew = 256 * 1024 * 1024; /* 256MB */
+ 
+ /*
   * map_addr_proc() is the routine called when the system is to
   * choose an address for the user.  We will pick an address
   * range which is just below the current stack limit.  The
   * algorithm used for cache consistency on machines with virtual
   * address caches is such that offset 0 in the vnode is always
*** 263,272 ****
--- 271,281 ----
           * Look for a large enough hole starting below the stack limit.
           * After finding it, use the upper part.
           */
          as_purge(as);
          off = off & (align_amount - 1);
+ 
          if (as_gap_aligned(as, len, &base, &slen, AH_HI, NULL, align_amount,
              PAGESIZE, off) == 0) {
                  caddr_t as_addr;
  
                  /*
*** 286,295 ****
--- 295,326 ----
                  addr += (long)off;
                  if (addr > as_addr) {
                          addr -= align_amount;
                  }
  
+                 /*
+                  * If randomization is requested, slew the allocation
+                  * backwards, within the same gap, by a random amount.
+                  */
+                 if (flags & _MAP_RANDOMIZE) {
+                         uint32_t slew;
+                         uint32_t maxslew;
+ 
+                         (void) random_get_pseudo_bytes((uint8_t *)&slew,
+                             sizeof (slew));
+ 
+                         maxslew = MIN(aslr_max_map_skew, (addr - base));
+                         /*
+                          * Don't allow ASLR to cause mappings to fail below
+                          * because of SF erratum #57
+                          */
+                         maxslew = MIN(maxslew, (addr - errata57_limit));
+ 
+                         slew = slew % maxslew;
+                         addr -= P2ALIGN(slew, align_amount);
+                 }
+ 
                  ASSERT(addr > base);
                  ASSERT(addr + len < base + slen);
                  ASSERT(((uintptr_t)addr & (align_amount - 1l)) ==
                      ((uintptr_t)(off)));
                  *addrp = addr;
*** 347,357 ****
  contig_mem_prealloc(caddr_t alloc_base, pgcnt_t npages)
  {
          /* not applicable to sun4u */
          return (alloc_base);
  }
- 
- size_t
- exec_get_spslew(void)
- {
-         return (0);
- }
--- 378,382 ----