Module Name: src
Committed By: thorpej
Date: Fri Sep 18 00:06:36 UTC 2020
Modified Files:
src/sys/arch/alpha/alpha: vm_machdep.c
Log Message:
Rather than having exception_return() at the root of the call graph for
kernel threads, provide a backstop that will prevent them from ever
accidentally trying to return to user space.
To generate a diff of this commit:
cvs rdiff -u -r1.116 -r1.117 src/sys/arch/alpha/alpha/vm_machdep.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/arch/alpha/alpha/vm_machdep.c
diff -u src/sys/arch/alpha/alpha/vm_machdep.c:1.116 src/sys/arch/alpha/alpha/vm_machdep.c:1.117
--- src/sys/arch/alpha/alpha/vm_machdep.c:1.116 Sat Aug 29 20:06:59 2020
+++ src/sys/arch/alpha/alpha/vm_machdep.c Fri Sep 18 00:06:35 2020
@@ -1,4 +1,4 @@
-/* $NetBSD: vm_machdep.c,v 1.116 2020/08/29 20:06:59 thorpej Exp $ */
+/* $NetBSD: vm_machdep.c,v 1.117 2020/09/18 00:06:35 thorpej Exp $ */
/*
* Copyright (c) 1994, 1995, 1996 Carnegie-Mellon University.
@@ -29,7 +29,7 @@
#include <sys/cdefs.h> /* RCS ID & Copyright macro defns */
-__KERNEL_RCSID(0, "$NetBSD: vm_machdep.c,v 1.116 2020/08/29 20:06:59 thorpej Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vm_machdep.c,v 1.117 2020/09/18 00:06:35 thorpej Exp $");
#include <sys/param.h>
#include <sys/systm.h>
@@ -60,6 +60,20 @@ cpu_lwp_free2(struct lwp *l)
}
/*
+ * This is a backstop used to ensure that kernel threads never do
+ * something silly like attempt to return to userspace. We achieve
+ * this by putting this at the root of their call graph instead of
+ * exception_return().
+ */
+void
+alpha_kthread_backstop(void)
+{
+ struct lwp * const l = curlwp;
+
+ panic("kthread lwp %p (%s) hit the backstop", l, l->l_name);
+}
+
+/*
* Finish a fork operation, with thread l2 nearly set up.
* Copy and update the pcb and trap frame, making the child ready to run.
*
@@ -130,6 +144,7 @@ cpu_lwp_fork(struct lwp *l1, struct lwp
*/
{
struct trapframe *l2tf;
+ uint64_t call_root;
/*
* Pick a stack pointer, leaving room for a trapframe;
@@ -148,12 +163,24 @@ cpu_lwp_fork(struct lwp *l1, struct lwp
l2tf->tf_regs[FRAME_A3] = 0; /* no error */
l2tf->tf_regs[FRAME_A4] = 1; /* is child */
+ /*
+ * Normal LWPs have their return address set to
+ * exception_return() so that they'll pop into
+ * user space. But kernel threads don't have
+ * a user space, so we put a backtop in place
+ * just in case they try.
+ */
+ if (__predict_true(l2->l_proc != &proc0))
+ call_root = (uint64_t)exception_return;
+ else
+ call_root = (uint64_t)alpha_kthread_backstop;
+
pcb2->pcb_hw.apcb_ksp =
(uint64_t)l2->l_md.md_tf;
pcb2->pcb_context[0] =
(uint64_t)func; /* s0: pc */
pcb2->pcb_context[1] =
- (uint64_t)exception_return; /* s1: ra */
+ call_root; /* s1: ra */
pcb2->pcb_context[2] =
(uint64_t)arg; /* s2: arg */
pcb2->pcb_context[3] =
