From cd9e9d1bc252b47dc480bc356a53ba08924e2852 Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Thu, 1 Nov 2012 15:17:43 +0000
Subject: [PATCH] Enable the new instructions for reading and writing bases for
 %fs, %gs, when supported.  Note that WRFSBASE and WRGSBASE are not very
 useful on FreeBSD right now, because a return from the kernel mode to
 userspace reloads the bases specified by the sysarch(2) syscall, most likely.

Enable the Supervisor Mode Execution Prevention (SMEP) when
supported. Since the loader(8) performs hand-off to the kernel with
the page tables which contradict the SMEP, postpone enabling the SMEP
on BSP until pmap switched for the proper kernel tables.

Debugged with the help from:	avg
Tested by:	avg, Michael Moll <kvedulv@kvedulv.de>
MFC after:	1 month
---
 sys/amd64/amd64/initcpu.c | 17 ++++++++++++++++-
 sys/amd64/amd64/pmap.c    |  2 ++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/sys/amd64/amd64/initcpu.c b/sys/amd64/amd64/initcpu.c
index 148b1ec3251..4abed4c0e6a 100644
--- a/sys/amd64/amd64/initcpu.c
+++ b/sys/amd64/amd64/initcpu.c
@@ -34,6 +34,7 @@ __FBSDID("$FreeBSD$");
 
 #include <sys/param.h>
 #include <sys/kernel.h>
+#include <sys/pcpu.h>
 #include <sys/systm.h>
 #include <sys/sysctl.h>
 
@@ -153,11 +154,25 @@ void
 initializecpu(void)
 {
 	uint64_t msr;
+	uint32_t cr4;
 
+	cr4 = rcr4();
 	if ((cpu_feature & CPUID_XMM) && (cpu_feature & CPUID_FXSR)) {
-		load_cr4(rcr4() | CR4_FXSR | CR4_XMM);
+		cr4 |= CR4_FXSR | CR4_XMM;
 		cpu_fxsr = hw_instruction_sse = 1;
 	}
+	if (cpu_stdext_feature & CPUID_STDEXT_FSGSBASE)
+		cr4 |= CR4_FSGSBASE;
+
+	/*
+	 * Postpone enabling the SMEP on the boot CPU until the page
+	 * tables are switched from the boot loader identity mapping
+	 * to the kernel tables.  The boot loader enables the U bit in
+	 * its tables.
+	 */
+	if (!IS_BSP() && (cpu_stdext_feature & CPUID_STDEXT_SMEP))
+		cr4 |= CR4_SMEP;
+	load_cr4(cr4);
 	if ((amd_feature & AMDID_NX) != 0) {
 		msr = rdmsr(MSR_EFER) | EFER_NXE;
 		wrmsr(MSR_EFER, msr);
diff --git a/sys/amd64/amd64/pmap.c b/sys/amd64/amd64/pmap.c
index 3098f2d31c7..a80fc7b8f5f 100644
--- a/sys/amd64/amd64/pmap.c
+++ b/sys/amd64/amd64/pmap.c
@@ -622,6 +622,8 @@ pmap_bootstrap(vm_paddr_t *firstaddr)
 	/* XXX do %cr0 as well */
 	load_cr4(rcr4() | CR4_PGE | CR4_PSE);
 	load_cr3(KPML4phys);
+	if (cpu_stdext_feature & CPUID_STDEXT_SMEP)
+		load_cr4(rcr4() | CR4_SMEP);
 
 	/*
 	 * Initialize the kernel pmap (which is statically allocated).