From 447e0dc2622e5b91035ca33e5d5b86ff8eb86d11 Mon Sep 17 00:00:00 2001
From: Taylor R Campbell <riastradh@NetBSD.org>
Date: Thu, 7 Apr 2022 18:14:04 +0000
Subject: [PATCH] x86: Assert SMAP stays put in CR4.

Apparently it isn't staying put, so maybe this will help to find
where it escaped.
---
 sys/arch/x86/x86/cpu.c   | 6 ++++++
 sys/arch/x86/x86/patch.c | 3 +++
 2 files changed, 9 insertions(+)

diff --git a/sys/arch/x86/x86/cpu.c b/sys/arch/x86/x86/cpu.c
index ba3a634a515f..b6cb761f8282 100644
--- a/sys/arch/x86/x86/cpu.c
+++ b/sys/arch/x86/x86/cpu.c
@@ -687,6 +687,9 @@ cpu_init(struct cpu_info *ci)
 		lcr4(cr4);
 	}
 
+	if (cpu_feature[5] & CPUID_SEF_SMAP)
+		KASSERT(rcr4() & CR4_SMAP);
+
 	/*
 	 * Changing CR4 register may change cpuid values. For example, setting
 	 * CR4_OSXSAVE sets CPUID2_OSXSAVE. The CPUID2_OSXSAVE is in
@@ -700,6 +703,9 @@ cpu_init(struct cpu_info *ci)
 		ci->ci_feat_val[1] = descs[2];
 	}
 
+	if (cpu_feature[5] & CPUID_SEF_SMAP)
+		KASSERT(rcr4() & CR4_SMAP);
+
 	if (x86_fpu_save >= FPU_SAVE_FXSAVE) {
 		fpuinit_mxcsr_mask();
 	}
diff --git a/sys/arch/x86/x86/patch.c b/sys/arch/x86/x86/patch.c
index 69efb230b05c..15cdf21d3dbb 100644
--- a/sys/arch/x86/x86/patch.c
+++ b/sys/arch/x86/x86/patch.c
@@ -308,6 +308,9 @@ x86_patch(bool early)
 {
 	static bool first, second;
 
+	if (!early && cpu_feature[5] & CPUID_SEF_SMAP)
+		KASSERT(rcr4() & CR4_SMAP);
+
 	if (early) {
 		if (first)
 			return;