Enable GCC stack protection (aka Propolice) for userland:

- It is opt-out for now so as to give it maximum testing, but it may be
  turned opt-in for stable branches depending on the consensus.  You
  can turn it off with WITHOUT_SSP.
- WITHOUT_SSP was previously used to disable the build of GNU libssp.
  It is harmless to steal the knob as SSP symbols have been provided
  by libc for a long time, GNU libssp should not have been much used.
- SSP is disabled in a few corners such as system bootstrap programs
  (sys/boot), process bootstrap code (rtld, csu) and SSP symbols themselves.
- It should be safe to use -fstack-protector-all to build world, however
  libc will be automatically downgraded to -fstack-protector because it
  breaks rtld otherwise.
- This option is unavailable on ia64.

Enable GCC stack protection (aka Propolice) for kernel:
- It is opt-out for now so as to give it maximum testing.
- Do not compile your kernel with -fstack-protector-all, it won't work.

Submitted by:	Jeremie Le Hen <jeremie@le-hen.org>

1 files changed, 35 insertions, 0 deletions

diff --git a/sys/kern/stack_protector.c b/sys/kern/stack_protector.c
new file mode 100644
index 0000000..9135c29
--- /dev/null
+++ b/sys/kern/stack_protector.c
@@ -0,0 +1,35 @@
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/types.h>
+#include <sys/param.h>
+#include <sys/kernel.h>
+#include <sys/systm.h>
+#include <sys/libkern.h>
+
+#if defined(__SSP__) || defined(__SSP_ALL__)
+long __stack_chk_guard[8] = {};
+void __stack_chk_fail(void);
+
+void
+__stack_chk_fail(void)
+{
+
+	panic("stack overflow detected; backtrace may be corrupted");
+}
+
+#define __arraycount(__x)	(sizeof(__x) / sizeof(__x[0]))
+static void
+__stack_chk_init(void *dummy __unused)
+{
+	size_t i;
+	long guard[__arraycount(__stack_chk_guard)];
+
+	arc4rand(guard, sizeof(guard), 0);
+	for (i = 0; i < __arraycount(guard); i++)
+		__stack_chk_guard[i] = guard[i];
+}
+/* SI_SUB_EVENTHANDLER is right after SI_SUB_LOCK used by arc4rand() init. */
+SYSINIT(stack_chk, SI_SUB_EVENTHANDLER, SI_ORDER_ANY, __stack_chk_init, NULL);
+
+#endif