Re: secmodel_securelevel(9) and machdep.svs.enabled

[Alexander Nasonov]

Alexander Nasonov wrote:
> When securelevel is set, should be lock 1->0 change for
> machdep.svs.enabled (and possibly for other sysctls related
> to recent security mitigations)?

Can I commit the attached patch? (doc update will follow)

-- 
Alex

Index: src/sys/sys/kauth.h
===================================================================
RCS file: /cvsroot/src/sys/sys/kauth.h,v
retrieving revision 1.75
diff -p -u -u -r1.75 kauth.h
--- src/sys/sys/kauth.h 28 Aug 2017 00:46:07 -0000      1.75
+++ src/sys/sys/kauth.h 24 Apr 2018 17:59:13 -0000
@@ -320,7 +320,8 @@ enum {
        KAUTH_MACHDEP_NVRAM,
        KAUTH_MACHDEP_UNMANAGEDMEM,
        KAUTH_MACHDEP_PXG,
-       KAUTH_MACHDEP_X86PMC
+       KAUTH_MACHDEP_X86PMC,
+       KAUTH_MACHDEP_SVS_DISABLE
 };
 
 /*
Index: src/sys/secmodel/suser/secmodel_suser.c
===================================================================
RCS file: /cvsroot/src/sys/secmodel/suser/secmodel_suser.c,v
retrieving revision 1.43
diff -p -u -u -r1.43 secmodel_suser.c
--- src/sys/secmodel/suser/secmodel_suser.c     14 Jun 2017 17:48:41 -0000      
1.43
+++ src/sys/secmodel/suser/secmodel_suser.c     24 Apr 2018 17:59:13 -0000
@@ -854,6 +854,7 @@ secmodel_suser_machdep_cb(kauth_cred_t c
        case KAUTH_MACHDEP_UNMANAGEDMEM:
        case KAUTH_MACHDEP_PXG:
        case KAUTH_MACHDEP_X86PMC:
+       case KAUTH_MACHDEP_SVS_DISABLE:
                if (isroot)
                        result = KAUTH_RESULT_ALLOW;
                break;
Index: src/sys/secmodel/securelevel/secmodel_securelevel.c
===================================================================
RCS file: /cvsroot/src/sys/secmodel/securelevel/secmodel_securelevel.c,v
retrieving revision 1.30
diff -p -u -u -r1.30 secmodel_securelevel.c
--- src/sys/secmodel/securelevel/secmodel_securelevel.c 25 Feb 2014 18:30:13 
-0000      1.30
+++ src/sys/secmodel/securelevel/secmodel_securelevel.c 24 Apr 2018 17:59:13 
-0000
@@ -494,6 +494,11 @@ secmodel_securelevel_machdep_cb(kauth_cr
                        result = KAUTH_RESULT_DENY;
                break;
 
+       case KAUTH_MACHDEP_SVS_DISABLE:
+               if (securelevel > 0)
+                       result = KAUTH_RESULT_DENY;
+               break;
+
        case KAUTH_MACHDEP_CPU_UCODE_APPLY:
                if (securelevel > 1)
                        result = KAUTH_RESULT_DENY;
Index: src/sys/arch/x86/x86/svs.c
===================================================================
RCS file: /cvsroot/src/sys/arch/x86/x86/svs.c,v
retrieving revision 1.17
diff -p -u -u -r1.17 svs.c
--- src/sys/arch/x86/x86/svs.c  30 Mar 2018 19:58:05 -0000      1.17
+++ src/sys/arch/x86/x86/svs.c  24 Apr 2018 17:59:11 -0000
@@ -38,6 +38,7 @@ __KERNEL_RCSID(0, "$NetBSD: svs.c,v 1.17
 #include <sys/systm.h>
 #include <sys/proc.h>
 #include <sys/cpu.h>
+#include <sys/kauth.h>
 #include <sys/sysctl.h>
 #include <sys/xcall.h>
 
@@ -737,11 +738,13 @@ sysctl_machdep_svs_enabled(SYSCTLFN_ARGS
                        error = 0;
                else
                        error = EOPNOTSUPP;
-       } else {
-               if (svs_enabled)
+       } else if (svs_enabled) {
+               error = kauth_authorize_machdep(kauth_cred_get(),
+                   KAUTH_MACHDEP_SVS_DISABLE, NULL, NULL, NULL, NULL);
+               if (!error)
                        error = svs_disable();
-               else
-                       error = 0;
+       } else {
+               error = 0;
        }
 
        return error;