[PATCH v2 5/6] x86/cpu: Remove "noexec"

Borislav Petkov
2022-01-27T11:56:54Z

From: Borislav Petkov <bp@suse.de>

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>
---
.../admin-guide/kernel-parameters.txt | 5 --
Documentation/x86/x86_64/boot-options.rst | 9 ---
arch/x86/include/asm/proto.h | 1 -
arch/x86/kernel/setup.c | 28 ++++++++-
arch/x86/mm/Makefile | 3 +-
arch/x86/mm/init_64.c | 1 -
arch/x86/mm/setup_nx.c | 62 -------------------
7 files changed, 26 insertions(+), 83 deletions(-)
delete mode 100644 arch/x86/mm/setup_nx.c

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index e3894159c22b..dd398f83b335 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3389,11 +3389,6 @@

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.
diff --git a/Documentation/x86/x86_64/boot-options.rst b/Documentation/x86/x86_64/boot-options.rst
index ccb7e86bf8d9..e72c60210285 100644
--- a/Documentation/x86/x86_64/boot-options.rst
+++ b/Documentation/x86/x86_64/boot-options.rst
@@ -164,15 +164,6 @@ 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
====

diff --git a/arch/x86/include/asm/proto.h b/arch/x86/include/asm/proto.h
index feed36d44d04..0f899c8d7a4e 100644
--- a/arch/x86/include/asm/proto.h
+++ b/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;

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index f7a132eb794d..07a395803957 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -740,6 +740,30 @@ 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
@@ -880,9 +904,7 @@ 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
- * again from within noexec_setup() during parsing early parameters
- * to honor the respective command line option.
+ * console setup can safely call set_fixmap()).
*/
x86_configure_nx();

diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile
index fe3d3061fc11..d957dc15b371 100644
--- a/arch/x86/mm/Makefile
+++ b/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
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 96d34ebb20a9..d2e484efdfa1 100644
--- a/arch/x86/mm/init_64.c
+++ b/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
diff --git a/arch/x86/mm/setup_nx.c b/arch/x86/mm/setup_nx.c
deleted file mode 100644
index ed5667f5169f..000000000000
--- a/arch/x86/mm/setup_nx.c
+++ /dev/null
@@ -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
- }
-}
--
2.29.2