x86/cpu: Remove "noexec"

It doesn't make any sense to disable non-executable mappings -
security-wise or else.

So rip out that switch and move the remaining code into setup.c and
delete setup_nx.c

Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Lai Jiangshan <jiangshanlai@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220127115626.14179-6-bp@alien8.de

Documentation/admin-guide/kernel-parameters.txt

@@ -3456,11 +3456,6 @@
 
 	noexec		[IA-64]
 
-	noexec		[X86]
-			On X86-32 available only on PAE configured kernels.
-			noexec=on: enable non-executable mappings (default)
-			noexec=off: disable non-executable mappings
-
 	nosmap		[PPC]
 			Disable SMAP (Supervisor Mode Access Prevention)
 			even if it is supported by processor.

Documentation/x86/x86_64/boot-options.rst

@@ -157,15 +157,6 @@ Rebooting
      newer BIOS, or newer board) using this option will ignore the built-in
      quirk table, and use the generic default reboot actions.
 
-Non Executable Mappings
-=======================
-
-  noexec=on|off
-    on
-      Enable(default)
-    off
-      Disable
-
 NUMA
 ====
 

arch/x86/include/asm/proto.h

@@ -35,7 +35,6 @@ void xen_entry_INT80_compat(void);
 #endif
 
 void x86_configure_nx(void);
-void x86_report_nx(void);
 
 extern int reboot_force;
 

arch/x86/kernel/setup.c

@@ -756,6 +756,30 @@ dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p)
 	return 0;
 }
 
+void x86_configure_nx(void)
+{
+	if (boot_cpu_has(X86_FEATURE_NX))
+		__supported_pte_mask |= _PAGE_NX;
+	else
+		__supported_pte_mask &= ~_PAGE_NX;
+}
+
+static void __init x86_report_nx(void)
+{
+	if (!boot_cpu_has(X86_FEATURE_NX)) {
+		printk(KERN_NOTICE "Notice: NX (Execute Disable) protection "
+		       "missing in CPU!\n");
+	} else {
+#if defined(CONFIG_X86_64) || defined(CONFIG_X86_PAE)
+		printk(KERN_INFO "NX (Execute Disable) protection: active\n");
+#else
+		/* 32bit non-PAE kernel, NX cannot be used */
+		printk(KERN_NOTICE "Notice: NX (Execute Disable) protection "
+		       "cannot be enabled: non-PAE kernel!\n");
+#endif
+	}
+}
+
 /*
  * Determine if we were loaded by an EFI loader.  If so, then we have also been
  * passed the efi memmap, systab, etc., so we should use these data structures
@@ -896,9 +920,7 @@ void __init setup_arch(char **cmdline_p)
 	/*
 	 * x86_configure_nx() is called before parse_early_param() to detect
 	 * whether hardware doesn't support NX (so that the early EHCI debug
-	 * console setup can safely call set_fixmap()). It may then be called
+	 * console setup can safely call set_fixmap()).
-	 * again from within noexec_setup() during parsing early parameters
-	 * to honor the respective command line option.
 	 */
 	x86_configure_nx();
 

arch/x86/mm/Makefile

@@ -20,13 +20,12 @@ CFLAGS_REMOVE_mem_encrypt_identity.o	= -pg
 endif
 
 obj-y				:=  init.o init_$(BITS).o fault.o ioremap.o extable.o mmap.o \
-				    pgtable.o physaddr.o setup_nx.o tlb.o cpu_entry_area.o maccess.o
+				    pgtable.o physaddr.o tlb.o cpu_entry_area.o maccess.o
 
 obj-y				+= pat/
 
 # Make sure __phys_addr has no stackprotector
 CFLAGS_physaddr.o		:= -fno-stack-protector
-CFLAGS_setup_nx.o		:= -fno-stack-protector
 CFLAGS_mem_encrypt_identity.o	:= -fno-stack-protector
 
 CFLAGS_fault.o := -I $(srctree)/$(src)/../include/asm/trace

arch/x86/mm/init_64.c

@@ -110,7 +110,6 @@ int force_personality32;
 /*
  * noexec32=on|off
  * Control non executable heap for 32bit processes.
- * To control the stack too use noexec=off
  *
  * on	PROT_READ does not imply PROT_EXEC for 32-bit processes (default)
  * off	PROT_READ implies PROT_EXEC

arch/x86/mm/setup_nx.c

@@ -1,62 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-#include <linux/spinlock.h>
-#include <linux/errno.h>
-#include <linux/init.h>
-#include <linux/pgtable.h>
-
-#include <asm/proto.h>
-#include <asm/cpufeature.h>
-
-static int disable_nx;
-
-/*
- * noexec = on|off
- *
- * Control non-executable mappings for processes.
- *
- * on      Enable
- * off     Disable
- */
-static int __init noexec_setup(char *str)
-{
-	if (!str)
-		return -EINVAL;
-	if (!strncmp(str, "on", 2)) {
-		disable_nx = 0;
-	} else if (!strncmp(str, "off", 3)) {
-		disable_nx = 1;
-	}
-	x86_configure_nx();
-	return 0;
-}
-early_param("noexec", noexec_setup);
-
-void x86_configure_nx(void)
-{
-	if (boot_cpu_has(X86_FEATURE_NX) && !disable_nx)
-		__supported_pte_mask |= _PAGE_NX;
-	else
-		__supported_pte_mask &= ~_PAGE_NX;
-}
-
-void __init x86_report_nx(void)
-{
-	if (!boot_cpu_has(X86_FEATURE_NX)) {
-		printk(KERN_NOTICE "Notice: NX (Execute Disable) protection "
-		       "missing in CPU!\n");
-	} else {
-#if defined(CONFIG_X86_64) || defined(CONFIG_X86_PAE)
-		if (disable_nx) {
-			printk(KERN_INFO "NX (Execute Disable) protection: "
-			       "disabled by kernel command line option\n");
-		} else {
-			printk(KERN_INFO "NX (Execute Disable) protection: "
-			       "active\n");
-		}
-#else
-		/* 32bit non-PAE kernel, NX cannot be used */
-		printk(KERN_NOTICE "Notice: NX (Execute Disable) protection "
-		       "cannot be enabled: non-PAE kernel!\n");
-#endif
-	}
-}