[src/trunk]: src/sys/kern - make pax aslr stack eat up to 1/8 of the max stac...

[christos <christos%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/ec9107a01faa
branches:  trunk
changeset: 345227:ec9107a01faa
user:      christos <christos%NetBSD.org@localhost>
date:      Fri May 13 17:33:43 2016 +0000

description:
- make pax aslr stack eat up to 1/8 of the max stack space insted of 1/4
  and reduce the length of the randomization bits since this is unused.
- call the pax aslr stack function sooner so we don't need to re-adjust the
  stack size.
- adjust the stack max resource limit to account for the maximum space that
  can be lost by aslr
- tidy up debugging printfs

diffstat:

 sys/kern/exec_subr.c |  36 ++++++++++++++++++------------------
 sys/kern/kern_pax.c  |  19 ++++++++++++-------
 2 files changed, 30 insertions(+), 25 deletions(-)

diffs (135 lines):

diff -r 074c9aad1d98 -r ec9107a01faa sys/kern/exec_subr.c
--- a/sys/kern/exec_subr.c      Fri May 13 16:54:36 2016 +0000
+++ b/sys/kern/exec_subr.c      Fri May 13 17:33:43 2016 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: exec_subr.c,v 1.74 2016/04/07 12:06:50 christos Exp $  */
+/*     $NetBSD: exec_subr.c,v 1.75 2016/05/13 17:33:43 christos Exp $  */
 
 /*
  * Copyright (c) 1993, 1994, 1996 Christopher G. Demetriou
@@ -31,7 +31,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: exec_subr.c,v 1.74 2016/04/07 12:06:50 christos Exp $");
+__KERNEL_RCSID(0, "$NetBSD: exec_subr.c,v 1.75 2016/05/13 17:33:43 christos Exp $");
 
 #include "opt_pax.h"
 
@@ -391,25 +391,27 @@
                max_stack_size = MAXSSIZ;
        }
 
-       DPRINTF(("ep_minsaddr=%llx max_stack_size=%llx\n",
-           (unsigned long long)epp->ep_minsaddr,
-           (unsigned long long)max_stack_size));
-
-       epp->ep_ssize = MIN(l->l_proc->p_rlimit[RLIMIT_STACK].rlim_cur,
-           max_stack_size);
+       DPRINTF(("ep_minsaddr=%#jx max_stack_size=%#jx\n",
+           (uintmax_t)epp->ep_minsaddr, (uintmax_t)max_stack_size));
 
 #ifdef PAX_ASLR
        pax_aslr_stack(epp, &max_stack_size);
 #endif /* PAX_ASLR */
 
+       DPRINTF(("[RLIMIT_STACK].lim_cur=%#jx max_stack_size=%#jx\n",
+           (uintmax_t)l->l_proc->p_rlimit[RLIMIT_STACK].rlim_cur,
+           (uintmax_t)max_stack_size));
+       epp->ep_ssize = MIN(l->l_proc->p_rlimit[RLIMIT_STACK].rlim_cur,
+           max_stack_size);
+
        l->l_proc->p_stackbase = epp->ep_minsaddr;
        
        epp->ep_maxsaddr = (vaddr_t)STACK_GROW(epp->ep_minsaddr,
-               max_stack_size);
+           max_stack_size);
 
-       DPRINTF(("ep_ssize=%llx ep_maxsaddr=%llx\n",
-           (unsigned long long)epp->ep_ssize,
-           (unsigned long long)epp->ep_maxsaddr));
+       DPRINTF(("ep_ssize=%#jx ep_minsaddr=%#jx ep_maxsaddr=%#jx\n",
+           (uintmax_t)epp->ep_ssize, (uintmax_t)epp->ep_minsaddr,
+           (uintmax_t)epp->ep_maxsaddr));
 
        /*
         * set up commands for stack.  note that this takes *two*, one to
@@ -425,12 +427,10 @@
        noaccess_linear_min = (vaddr_t)STACK_ALLOC(STACK_GROW(epp->ep_minsaddr,
            access_size), noaccess_size);
 
-       DPRINTF(("access_size=%llx, access_linear_min=%llx, "
-           "noaccess_size=%llx, noaccess_linear_min=%llx\n",
-           (unsigned long long)access_size,
-           (unsigned long long)access_linear_min,
-           (unsigned long long)noaccess_size,
-           (unsigned long long)noaccess_linear_min));
+       DPRINTF(("access_size=%#jx, access_linear_min=%#jx, "
+           "noaccess_size=%#jx, noaccess_linear_min=%#jx\n",
+           (uintmax_t)access_size, (uintmax_t)access_linear_min,
+           (uintmax_t)noaccess_size, (uintmax_t)noaccess_linear_min));
 
        if (noaccess_size > 0 && noaccess_size <= MAXSSIZ) {
                NEW_VMCMD2(&epp->ep_vmcmds, vmcmd_map_zero, noaccess_size,
diff -r 074c9aad1d98 -r ec9107a01faa sys/kern/kern_pax.c
--- a/sys/kern/kern_pax.c       Fri May 13 16:54:36 2016 +0000
+++ b/sys/kern/kern_pax.c       Fri May 13 17:33:43 2016 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: kern_pax.c,v 1.43 2016/05/08 20:01:56 christos Exp $   */
+/*     $NetBSD: kern_pax.c,v 1.44 2016/05/13 17:33:43 christos Exp $   */
 
 /*
  * Copyright (c) 2015 The NetBSD Foundation, Inc.
@@ -57,7 +57,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_pax.c,v 1.43 2016/05/08 20:01:56 christos Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_pax.c,v 1.44 2016/05/13 17:33:43 christos Exp $");
 
 #include "opt_pax.h"
 
@@ -104,11 +104,12 @@
 #define PAX_ASLR_DELTA_STACK_LSB       PGSHIFT
 #endif
 #ifndef PAX_ASLR_DELTA_STACK_LEN
-#define PAX_ASLR_DELTA_STACK_LEN       PAX_ASLR_DELTA_MMAP_LEN
+#define PAX_ASLR_DELTA_STACK_LEN       ((sizeof(void *) * NBBY) / 4)
 #endif
 #ifndef PAX_ASLR_DELTA_STACK_LEN32
-#define PAX_ASLR_DELTA_STACK_LEN32     PAX_ASLR_DELTA_MMAP_LEN32
+#define PAX_ASLR_DELTA_STACK_LEN32     ((sizeof(uint32_t) * NBBY) / 4)
 #endif
+#define PAX_ASLR_MAX_STACK_WASTE       8
 
 static bool pax_aslr_elf_flags_active(uint32_t);
 #endif /* PAX_ASLR */
@@ -335,6 +336,12 @@
                panic("pax_init: segvguard_id: error=%d\n", error);
        }
 #endif /* PAX_SEGVGUARD */
+#ifdef PAX_ASLR
+       /* Adjust maximum stack by the size we can consume for ASLR */
+       extern rlim_t maxsmap;
+       maxsmap = MAXSSIZ - (MAXSSIZ / PAX_ASLR_MAX_STACK_WASTE);
+       // XXX: compat32 is not handled.
+#endif
 }
 
 void
@@ -564,14 +571,12 @@
                rand = pax_aslr_rand;
 #endif
        u_long d = PAX_ASLR_DELTA(rand, PAX_ASLR_DELTA_STACK_LSB, len);
-       d &= (*max_stack_size / 4) - 1;
+       d &= (*max_stack_size / PAX_ASLR_MAX_STACK_WASTE) - 1;
        u_long newminsaddr = (u_long)STACK_GROW(epp->ep_minsaddr, d);
        PAX_DPRINTF("old minsaddr=%#jx delta=%#lx new minsaddr=%#lx",
            (uintmax_t)epp->ep_minsaddr, d, newminsaddr);
        epp->ep_minsaddr = (vaddr_t)newminsaddr;
        *max_stack_size -= d;
-       if (epp->ep_ssize > *max_stack_size)
-               epp->ep_ssize = *max_stack_size;
 }
 
 uint32_t