kernel: fix taking smep/smap path on unsupported systems

kernel-src/arch/x86-64/cpu.c

@@ -17,6 +17,7 @@
 
 static bool has_smap;
 static bool has_smap_detected;
+static bool has_smep;
 
 void arch_syscall_entry();
 static void illisr(isr_t *self, context_t *ctx) {
@@ -79,6 +80,7 @@ static void enable_smep_if_available(void) {
 	asm volatile("mov %%cr4, %0" : "=r"(cr4));
 	cr4 |= CR4_SMEP;
 	asm volatile("mov %0, %%cr4" : : "r"(cr4) : "memory");
+	has_smep = true;
 }
 
 static bool detect_smap(void) {
@@ -115,6 +117,14 @@ void arch_cpu_user_access_end(void) {
 		asm volatile("clac" : : : "memory");
 }
 
+bool arch_cpu_smep_enabled(void) {
+	return has_smep;
+}
+
+bool arch_cpu_smap_enabled(void) {
+	return has_smap;
+}
+
 void arch_nmi_isr(context_t *ctx) {
 	// we are in an NMI context, running on IST0 
 	// first load the proper gsbase to get access to cpu-local variables. 

kernel-src/arch/x86-64/mmu.c

@@ -324,8 +324,14 @@ static volatile struct limine_executable_address_request kaddrreq = {
 #define ERROR_FETCH   16
 
 static void pfisr(isr_t *self, context_t *ctx) {
-	if ((ctx->rflags & ARCH_CONTEXT_RFLAGS_AC) == 0 && IS_USER_ADDRESS((void *)ctx->cr2) && !IS_USER_ADDRESS((void *)ctx->rip)) {
-		_panic("SMAP/SMEP violation", ctx);
+	if (!ARCH_CONTEXT_ISUSER(ctx) && IS_USER_ADDRESS((void *)ctx->cr2)) {
+		if ((ctx->error & ERROR_FETCH) && arch_cpu_smep_enabled()) {
+			_panic("SMEP violation", ctx);
+		}
+
+		if ((ctx->error & ERROR_FETCH) == 0 && (ctx->rflags & ARCH_CONTEXT_RFLAGS_AC) == 0 && arch_cpu_smap_enabled()) {
+			_panic("SMAP violation", ctx);
+		}
 	}
 
 	thread_t *thread = current_thread();

kernel-src/include/x86-64/arch/cpu.h

@@ -116,6 +116,8 @@ static inline uint16_t be_to_cpu_w(uint16_t w) {
 cpu_t *get_bsp(void);
 void arch_cpu_user_access_begin(void);
 void arch_cpu_user_access_end(void);
+bool arch_cpu_smep_enabled(void);
+bool arch_cpu_smap_enabled(void);
 
 static inline thread_t *current_thread(void) {
 	thread_t *thread;