Map the sigcode page copy-on-write. This allows userland to put breakpoints

in the signal trampoline.  Solves some long-standing issues with debugging
signal handlers in GDB.

ok deraadt@

diff --git a/sys/kern/kern_exec.c b/sys/kern/kern_exec.c
index cad14a4..cfddf50 100644 (file)
--- a/sys/kern/kern_exec.c
+++ b/sys/kern/kern_exec.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: kern_exec.c,v 1.153 2014/12/17 06:58:11 guenther Exp $        */
+/*     $OpenBSD: kern_exec.c,v 1.154 2015/01/15 10:04:26 kettenis Exp $        */
 /*     $NetBSD: kern_exec.c,v 1.75 1996/02/09 18:59:28 christos Exp $  */
 
 /*-
@@ -848,7 +848,8 @@ exec_sigcode_map(struct process *pr, struct emul *e)
        uao_reference(e->e_sigobject);
        if (uvm_map(&pr->ps_vmspace->vm_map, &pr->ps_sigcode, round_page(sz),
            e->e_sigobject, 0, 0, UVM_MAPFLAG(PROT_READ | PROT_EXEC,
-           PROT_READ | PROT_EXEC, MAP_INHERIT_SHARE, MADV_RANDOM, 0))) {
+           PROT_READ | PROT_WRITE | PROT_EXEC, MAP_INHERIT_SHARE,
+           MADV_RANDOM, UVM_FLAG_COPYONW))) {
                uao_detach(e->e_sigobject);
                return (ENOMEM);
        }