[src/trunk]: src/sys/dev/nvmm In nvmm_open(), make sure an implementation was...

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

details:   https://anonhg.NetBSD.org/src/rev/3cde414642bb
branches:  trunk
changeset: 931335:3cde414642bb
user:      maxv <maxv%NetBSD.org@localhost>
date:      Sun Apr 26 19:31:36 2020 +0000

description:
In nvmm_open(), make sure an implementation was found. This fixes an
initialization bug triggerable in certain conditions.

If you build nvmm inside the kernel, AND have a cpu that is not supported,
AND run nvmmctl (or qemu-nvmm, both being the only binaries in the "nvmm"
group), you get a page fault.

This is because when nvmm is built inside the kernel, the kernel registers
nvmm_cdevsw behind nvmm's back. The ioctl is therefore always accessible,
and will hit NULL pointers if nvmm_init() failed.

Problem reported by Andrei M. on netbsd-users@, thanks.

diffstat:

 sys/dev/nvmm/nvmm.c |  6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diffs (27 lines):

diff -r 635ed80e4925 -r 3cde414642bb sys/dev/nvmm/nvmm.c
--- a/sys/dev/nvmm/nvmm.c       Sun Apr 26 19:18:52 2020 +0000
+++ b/sys/dev/nvmm/nvmm.c       Sun Apr 26 19:31:36 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: nvmm.c,v 1.25 2019/10/28 09:00:08 maxv Exp $   */
+/*     $NetBSD: nvmm.c,v 1.26 2020/04/26 19:31:36 maxv Exp $   */
 
 /*
  * Copyright (c) 2018-2019 The NetBSD Foundation, Inc.
@@ -30,7 +30,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: nvmm.c,v 1.25 2019/10/28 09:00:08 maxv Exp $");
+__KERNEL_RCSID(0, "$NetBSD: nvmm.c,v 1.26 2020/04/26 19:31:36 maxv Exp $");
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -1040,6 +1040,8 @@
        struct file *fp;
        int error, fd;
 
+       if (__predict_false(nvmm_impl == NULL))
+               return ENXIO;
        if (minor(dev) != 0)
                return EXDEV;
        if (!(flags & O_CLOEXEC))