[RFC v4 05/10] S.A.R.A. WX Protection

[Salvatore Mesoraca]

Introduction of S.A.R.A. WX Protection.
It aims to improve user-space programs security by applying:
- W^X enforcement
- W!->X (once writable never executable) mprotect restriction
- Executable MMAP prevention

All of the above features can be enabled or disabled both system wide
or on a per executable basis through the use of configuration.
W^X enforcement works by blocking any memory allocation or mprotect
invocation with both the WRITE and the EXEC flags enabled.
W!->X restriction works by preventing any mprotect invocation that makes
executable any page that is flagged VM_MAYWRITE.
This feature can be configured separately for stack, heap and other
allocations.
Executable MMAP prevention works by preventing any new executable
allocation after the dynamic libraries have been loaded. It works under the
assumption that, when the dynamic libraries have been finished loading, the
RELRO section will be marked read only.

Parts of WX Protection are inspired by some of the features available in
PaX according to my understanding of the code. Changes or omissions from
the original code are mine and don't reflect the original grsecurity/PaX
code.

Signed-off-by: Salvatore Mesoraca <s.mesoraca16@xxxxxxxxx>
---
 security/sara/Kconfig          |  74 ++++
 security/sara/Makefile         |   1 +
 security/sara/include/utils.h  |  11 +
 security/sara/include/wxprot.h |  27 ++
 security/sara/main.c           |   6 +
 security/sara/wxprot.c         | 741 +++++++++++++++++++++++++++++++++++++++++
 6 files changed, 860 insertions(+)
 create mode 100644 security/sara/include/wxprot.h
 create mode 100644 security/sara/wxprot.c

diff --git a/security/sara/Kconfig b/security/sara/Kconfig
index 0456220..62dfe4f 100644
--- a/security/sara/Kconfig
+++ b/security/sara/Kconfig
@@ -38,3 +38,77 @@ config SECURITY_SARA_NO_RUNTIME_ENABLE
 
 	  If unsure, answer Y.
 
+config SECURITY_SARA_WXPROT
+	bool "WX Protection: W^X and W!->X protections"
+	depends on SECURITY_SARA
+	default y
+	help
+	  WX Protection aims to improve user-space programs security by applying:
+	    - W^X memory restriction
+	    - W!->X (once writable never executable) mprotect restriction
+	    - Executable MMAP prevention
+	  See Documentation/admin-guide/LSM/SARA.rst. for further information.
+
+	  If unsure, answer Y.
+
+choice
+	prompt "Default action for W^X and W!->X protections"
+	depends on SECURITY_SARA
+	depends on SECURITY_SARA_WXPROT
+	default SECURITY_SARA_WXPROT_DEFAULT_FLAGS_ALL_COMPLAIN_VERBOSE
+
+        help
+	  Choose the default behaviour of WX Protection when no config
+	  rule matches or no rule is loaded.
+	  For further information on available flags and their meaning
+	  see Documentation/admin-guide/LSM/SARA.rst.
+
+	config SECURITY_SARA_WXPROT_DEFAULT_FLAGS_ALL_COMPLAIN_VERBOSE
+		bool "Protections enabled but not enforced."
+		help
+		  All features enabled except "Executable MMAP prevention",
+		  verbose reporting, but no actual enforce: it just complains.
+		  Its numeric value is 0x3f, for more information see
+		  Documentation/admin-guide/LSM/SARA.rst.
+
+        config SECURITY_SARA_WXPROT_DEFAULT_FLAGS_ALL_ENFORCE_VERBOSE
+		bool "Full protection, verbose."
+		help
+		  All features enabled except "Executable MMAP prevention".
+		  The enabled features will be enforced with verbose reporting.
+		  Its numeric value is 0x2f, for more information see
+		  Documentation/admin-guide/LSM/SARA.rst.
+
+        config SECURITY_SARA_WXPROT_DEFAULT_FLAGS_ALL_ENFORCE
+		bool "Full protection, quiet."
+		help
+		  All features enabled except "Executable MMAP prevention".
+		  The enabled features will be enforced quietly.
+		  Its numeric value is 0xf, for more information see
+		  Documentation/admin-guide/LSM/SARA.rst.
+
+	config SECURITY_SARA_WXPROT_DEFAULT_FLAGS_NONE
+		bool "No protection at all."
+		help
+		  All features disabled.
+		  Its numeric value is 0, for more information see
+		  Documentation/admin-guide/LSM/SARA.rst.
+endchoice
+
+config SECURITY_SARA_WXPROT_DISABLED
+	bool "WX protection will be disabled at boot."
+	depends on SECURITY_SARA_WXPROT
+	default n
+	help
+	  If you say Y here WX protection won't be enabled at startup. You can
+	  override this option via user-space utilities or at boot time via
+	  "sara.wxprot_enabled=[0|1]" kernel parameter.
+
+	  If unsure, answer N.
+
+config SECURITY_SARA_WXPROT_DEFAULT_FLAGS
+	hex
+	default "0x3f" if SECURITY_SARA_WXPROT_DEFAULT_FLAGS_ALL_COMPLAIN_VERBOSE
+	default "0x2f" if SECURITY_SARA_WXPROT_DEFAULT_FLAGS_ALL_ENFORCE_VERBOSE
+	default "0xf" if SECURITY_SARA_WXPROT_DEFAULT_FLAGS_ALL_ENFORCE
+	default "0" if SECURITY_SARA_WXPROT_DEFAULT_FLAGS_NONE
diff --git a/security/sara/Makefile b/security/sara/Makefile
index 14bf7a8..74a3338 100644
--- a/security/sara/Makefile
+++ b/security/sara/Makefile
@@ -1,3 +1,4 @@
 obj-$(CONFIG_SECURITY_SARA) := sara.o
 
 sara-y := main.o securityfs.o utils.o sara_data.o
+sara-$(CONFIG_SECURITY_SARA_WXPROT) += wxprot.o
diff --git a/security/sara/include/utils.h b/security/sara/include/utils.h
index 166b9ed..579287f 100644
--- a/security/sara/include/utils.h
+++ b/security/sara/include/utils.h
@@ -26,6 +26,17 @@ static inline void release_entry(struct kref *ref)
 	/* All work is done after the return from kref_put(). */
 }
 
+
+/*
+ * The following macros must be used to access S.A.R.A. configuration
+ * structures.
+ * They are thread-safe under the assumption that a configuration
+ * won't ever be deleted but just replaced using SARA_CONFIG_REPLACE,
+ * possibly using an empty configuration.
+ * i.e. every call to SARA_CONFIG_PUT *must* be preceded by a matching
+ * SARA_CONFIG_GET invocation.
+ */
+
 #define SARA_CONFIG_GET_RCU(DEST, CONFIG) do {	\
 	rcu_read_lock();			\
 	DEST = rcu_dereference(CONFIG);		\
diff --git a/security/sara/include/wxprot.h b/security/sara/include/wxprot.h
new file mode 100644
index 0000000..23b8a7b
--- /dev/null
+++ b/security/sara/include/wxprot.h
@@ -0,0 +1,27 @@
+/*
+ * S.A.R.A. Linux Security Module
+ *
+ * Copyright (C) 2017 Salvatore Mesoraca <s.mesoraca16@xxxxxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2, as
+ * published by the Free Software Foundation.
+ *
+ */
+
+#ifndef __SARA_WXPROT_H
+#define __SARA_WXPROT_H
+
+#ifdef CONFIG_SECURITY_SARA_WXPROT
+
+#include <linux/init.h>
+int sara_wxprot_init(void) __init;
+
+#else /* CONFIG_SECURITY_SARA_WXPROT */
+inline int sara_wxprot_init(void)
+{
+	return 0;
+}
+#endif /* CONFIG_SECURITY_SARA_WXPROT */
+
+#endif /* __SARA_WXPROT_H */
diff --git a/security/sara/main.c b/security/sara/main.c
index 0fc1761..728c859 100644
--- a/security/sara/main.c
+++ b/security/sara/main.c
@@ -17,6 +17,7 @@
 #include "include/sara.h"
 #include "include/sara_data.h"
 #include "include/securityfs.h"
+#include "include/wxprot.h"
 
 static const int sara_version = SARA_VERSION;
 
@@ -96,6 +97,11 @@ void __init sara_init(void)
 		goto error;
 	}
 
+	if (sara_wxprot_init()) {
+		pr_crit("impossible to initialize WX protections.\n");
+		goto error;
+	}
+
 	pr_debug("initialized.\n");
 
 	if (sara_enabled)
diff --git a/security/sara/wxprot.c b/security/sara/wxprot.c
new file mode 100644
index 0000000..46600f0
--- /dev/null
+++ b/security/sara/wxprot.c
@@ -0,0 +1,741 @@
+/*
+ * S.A.R.A. Linux Security Module
+ *
+ * Copyright (C) 2017 Salvatore Mesoraca <s.mesoraca16@xxxxxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2, as
+ * published by the Free Software Foundation.
+ *
+ */
+
+#ifdef CONFIG_SECURITY_SARA_WXPROT
+
+#include <linux/binfmts.h>
+#include <linux/cred.h>
+#include <linux/elf.h>
+#include <linux/kref.h>
+#include <linux/lsm_hooks.h>
+#include <linux/mm.h>
+#include <linux/mman.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+#include <linux/ratelimit.h>
+#include <linux/spinlock.h>
+
+#include "include/sara.h"
+#include "include/sara_data.h"
+#include "include/utils.h"
+#include "include/securityfs.h"
+#include "include/wxprot.h"
+
+#define SARA_WXPROT_CONFIG_VERSION 0
+
+#define SARA_WXP_HEAP		0x0001
+#define SARA_WXP_STACK		0x0002
+#define SARA_WXP_OTHER		0x0004
+#define SARA_WXP_WXORX		0x0008
+#define SARA_WXP_COMPLAIN	0x0010
+#define SARA_WXP_VERBOSE	0x0020
+#define SARA_WXP_MMAP		0x0040
+#define SARA_WXP_TRANSFER	0x0200
+#define SARA_WXP_NONE		0x0000
+#define SARA_WXP_MPROTECT	(SARA_WXP_HEAP	| \
+				SARA_WXP_STACK	| \
+				SARA_WXP_OTHER)
+#define __SARA_WXP_ALL		(SARA_WXP_MPROTECT	| \
+				SARA_WXP_MMAP		| \
+				SARA_WXP_WXORX		| \
+				SARA_WXP_COMPLAIN	| \
+				SARA_WXP_VERBOSE)
+#define SARA_WXP_ALL		__SARA_WXP_ALL
+
+struct wxprot_rule {
+	char *path;
+	u16 flags;
+	bool exact;
+};
+
+struct wxprot_config_container {
+	u32 rules_size;
+	struct wxprot_rule *rules;
+	size_t buf_len;
+	struct kref refcount;
+	char hash[SARA_CONFIG_HASH_LEN];
+};
+
+static struct wxprot_config_container __rcu *wxprot_config;
+
+static const int wxprot_config_version = SARA_WXPROT_CONFIG_VERSION;
+static bool wxprot_enabled __read_mostly = true;
+static DEFINE_SPINLOCK(wxprot_config_lock);
+
+static u16 default_flags __ro_after_init =
+				CONFIG_SECURITY_SARA_WXPROT_DEFAULT_FLAGS;
+
+static const bool wxprot_emutramp;
+
+static void pr_wxp(char *msg)
+{
+	char *buf, *path;
+
+	path = get_current_path(&buf);
+	pr_notice_ratelimited("WXP: %s in '%s' (%d).\n",
+			      msg, path, current->pid);
+	kvfree(buf);
+}
+
+/**
+ * are_flags_valid - check whether the given combination of flags is valid
+ * @flags: the flags to be checked
+ *
+ * Returns true if flags are valid, false otherwise.
+ *
+ * Rules checked:
+ *   - Unused bits must be set to 0.
+ *   - Any feature in the "MPROTECT" group require "WXORX".
+ *   - "COMPLAIN" and "VERBOSE" can only be used if some other feature is
+ *     enabled.
+ *   - Trampoline emulation can only be used when all "MPROTECT"
+ *     features are active.
+ *   - "MMAP" protection requires SARA_WXP_OTHER
+ */
+static bool are_flags_valid(u16 flags)
+{
+	flags &= ~SARA_WXP_TRANSFER;
+	if (unlikely((flags & SARA_WXP_ALL) != flags))
+		return false;
+	if (unlikely(flags & SARA_WXP_MPROTECT &&
+		     !(flags & SARA_WXP_WXORX)))
+		return false;
+	if (unlikely(flags & (SARA_WXP_COMPLAIN | SARA_WXP_VERBOSE) &&
+		     !(flags & (SARA_WXP_MPROTECT |
+				SARA_WXP_WXORX |
+				SARA_WXP_MMAP))))
+		return false;
+	if (unlikely(flags & SARA_WXP_MMAP &&
+		     !(flags & SARA_WXP_OTHER)))
+		return false;
+	return true;
+}
+
+module_param(wxprot_enabled, bool, 0);
+MODULE_PARM_DESC(wxprot_enabled, "Disable or enable S.A.R.A. WX Protection at boot time.");
+
+static int param_set_wxpflags(const char *val, const struct kernel_param *kp)
+{
+	u16 flags;
+
+	if (!val || kstrtou16(val, 0, &flags) != 0 || !are_flags_valid(flags))
+		return -EINVAL;
+	*(u16 *) kp->arg = flags;
+	return 0;
+}
+
+static struct kernel_param_ops param_ops_wxpflags = {
+	.set = param_set_wxpflags,
+};
+
+#define param_check_wxpflags(name, p) __param_check(name, p, u16)
+
+module_param_named(wxprot_default_flags, default_flags, wxpflags, 0);
+MODULE_PARM_DESC(wxprot_default_flags, "Disable or enable S.A.R.A. WX Protection at boot time.");
+
+/*
+ * MMAP exec restriction
+ */
+#define PT_GNU_RELRO (PT_LOOS + 0x474e552)
+
+union elfh {
+	struct elf32_hdr c32;
+	struct elf64_hdr c64;
+};
+
+union elfp {
+	struct elf32_phdr c32;
+	struct elf64_phdr c64;
+};
+
+#define find_relro_section(ELFH, ELFP, FILE, RELRO, FOUND) do {		\
+	unsigned long i;						\
+	int _tmp;							\
+	loff_t _pos = 0;						\
+	if (ELFH.e_type == ET_DYN || ELFH.e_type == ET_EXEC) {		\
+		for (i = 0; i < ELFH.e_phnum; ++i) {			\
+			_pos = ELFH.e_phoff + i*sizeof(ELFP);		\
+			_tmp = kernel_read(FILE, &ELFP, sizeof(ELFP),	\
+					   &_pos);			\
+			if (_tmp != sizeof(ELFP))			\
+				break;					\
+			if (ELFP.p_type == PT_GNU_RELRO) {		\
+				RELRO = ELFP.p_offset >> PAGE_SHIFT;	\
+				FOUND = true;				\
+				break;					\
+			}						\
+		}							\
+	}								\
+} while (0)
+
+static int set_relro_page(struct linux_binprm *bprm)
+{
+	union elfh elf_h;
+	union elfp elf_p;
+	unsigned long relro_page = 0;
+	bool relro_page_found = false;
+	int ret;
+	loff_t pos = 0;
+
+	ret = kernel_read(bprm->file, &elf_h, sizeof(elf_h), &pos);
+	if (ret == sizeof(elf_h) &&
+	    strncmp(elf_h.c32.e_ident, ELFMAG, SELFMAG) == 0) {
+		if (elf_h.c32.e_ident[EI_CLASS] == ELFCLASS32) {
+			find_relro_section(elf_h.c32,
+					   elf_p.c32,
+					   bprm->file,
+					   relro_page,
+					   relro_page_found);
+		} else if (IS_ENABLED(CONFIG_64BIT) &&
+			   elf_h.c64.e_ident[EI_CLASS] == ELFCLASS64) {
+			find_relro_section(elf_h.c64,
+					   elf_p.c64,
+					   bprm->file,
+					   relro_page,
+					   relro_page_found);
+		}
+	} else
+		return 2; /* It isn't an ELF */
+
+	if (relro_page_found) {
+		get_sara_relro_page(bprm->cred) = relro_page;
+		get_sara_relro_page_found(bprm->cred) = relro_page_found;
+		get_sara_relro_file(bprm->cred) = bprm->file;
+		return 0;
+	} else
+		return 1; /* It's an ELF without a RELRO section */
+}
+
+static inline int is_relro_page(const struct vm_area_struct *vma)
+{
+	if (get_current_sara_relro_page_found() &&
+	    get_current_sara_relro_page() == vma->vm_pgoff &&
+	    get_current_sara_relro_file() == vma->vm_file)
+		return 1;
+	return 0;
+}
+
+/*
+ * LSM hooks
+ */
+static int sara_bprm_set_creds(struct linux_binprm *bprm)
+{
+	int i;
+	struct wxprot_config_container *c;
+	u16 sara_wxp_flags = default_flags;
+	char *buf = NULL;
+	char *path = NULL;
+	struct cred *current_new;
+
+	sara_wxp_flags = get_sara_wxp_flags(bprm->cred);
+	get_sara_mmap_blocked(bprm->cred) = false;
+	get_sara_relro_page_found(bprm->cred) = false;
+	get_sara_relro_page(bprm->cred) = 0;
+	get_sara_relro_file(bprm->cred) = NULL;
+	get_sara_wxp_flags(bprm->cred) = SARA_WXP_NONE;
+	get_sara_execve_flags(bprm->cred) = SARA_WXP_NONE;
+
+	if (!sara_enabled || !wxprot_enabled)
+		return 0;
+
+	/*
+	 * SARA_WXP_TRANSFER means that the parent
+	 * wants this child to inherit its flags.
+	 */
+	if (!(sara_wxp_flags & SARA_WXP_TRANSFER)) {
+		sara_wxp_flags = default_flags;
+		path = get_absolute_path(&bprm->file->f_path, &buf);
+		if (IS_ERR(path)) {
+			path = (char *) bprm->interp;
+			if (PTR_ERR(path) == -ENAMETOOLONG)
+				pr_warn_ratelimited("WXP: path too long for '%s'. Default flags will be used.\n",
+						path);
+			else
+				pr_warn_ratelimited("WXP: can't find path for '%s'. Default flags will be used.\n",
+						path);
+			goto skip_flags;
+		}
+		SARA_CONFIG_GET_RCU(c, wxprot_config);
+		for (i = 0; i < c->rules_size; ++i) {
+			if ((c->rules[i].exact &&
+			     strcmp(c->rules[i].path, path) == 0) ||
+			    (!c->rules[i].exact &&
+			     strncmp(c->rules[i].path, path,
+				     strlen(c->rules[i].path)) == 0)) {
+				sara_wxp_flags = c->rules[i].flags;
+				/* most specific path always come first */
+				break;
+			}
+		}
+		SARA_CONFIG_PUT_RCU(c);
+	} else
+		path = (char *) bprm->interp;
+
+	if (sara_wxp_flags != default_flags &&
+	    sara_wxp_flags & SARA_WXP_VERBOSE)
+		pr_debug_ratelimited("WXP: '%s' run with flags '0x%x'.\n",
+				     path, sara_wxp_flags);
+
+skip_flags:
+	i = set_relro_page(bprm);
+	/*
+	 * i != 0 means no relro segment
+	 * i == 1 means the file wasn't an ELF
+	 *
+	 * We want to disable SARA_WXP_MMAP when the file is missing
+	 * the RELRO segment.
+	 * We want to verbosely report this case only if the file
+	 * was an ELF.
+	 *
+	 */
+	if (i != 0) {
+		if (sara_wxp_flags & SARA_WXP_VERBOSE &&
+		    sara_wxp_flags & SARA_WXP_MMAP &&
+		    i == 1)
+			pr_notice_ratelimited("WXP: failed to find RELRO section in '%s'.\n",
+					      path);
+		sara_wxp_flags &= ~SARA_WXP_MMAP;
+	}
+	kvfree(buf);
+	get_sara_wxp_flags(bprm->cred) = sara_wxp_flags;
+
+	/*
+	 * Set the flags to be used for validation
+	 * during the execve and discard SARA_WXP_MMAP:
+	 * it doesn't make sense to prevent executable
+	 * mmap during execve.
+	 */
+	current_new = prepare_creds();
+	if (unlikely(current_new == NULL))
+		return -ENOMEM;
+	get_sara_execve_flags(current_new) = sara_wxp_flags & ~SARA_WXP_MMAP;
+	commit_creds(current_new);
+
+	return 0;
+}
+
+#define sara_warn_or_return(err, msg) do {		\
+	if ((sara_wxp_flags & SARA_WXP_VERBOSE))	\
+		pr_wxp(msg);				\
+	if (!(sara_wxp_flags & SARA_WXP_COMPLAIN))	\
+		return -err;				\
+} while (0)
+
+static int sara_check_vmflags(vm_flags_t vm_flags)
+{
+	u16 sara_wxp_flags;
+
+	if (!sara_enabled || !wxprot_enabled)
+		return 0;
+
+	/*
+	 * Memory allocations done during an execve should be
+	 * checked against the rules of the new executable,
+	 * instead of those of the current one.
+	 */
+	if (current->in_execve)
+		sara_wxp_flags = get_current_sara_execve_flags();
+	else
+		sara_wxp_flags = get_current_sara_wxp_flags();
+
+	/*
+	 * Be quiet when using security_check_vmflags to decide
+	 * what to do with a PT_GNU_STACK header
+	 */
+	if (current->in_execve && vm_flags == (VM_EXEC|VM_READ|VM_WRITE))
+		sara_wxp_flags &= ~SARA_WXP_VERBOSE;
+
+	/*
+	 * If "W xor X" is active for the current thread
+	 * this function must not allow new allocations that
+	 * have both the VM_WRITE and the VM_EXEC flags.
+	 */
+	if (sara_wxp_flags & SARA_WXP_WXORX &&
+	    vm_flags & VM_WRITE &&
+	    vm_flags & VM_EXEC)
+		sara_warn_or_return(EPERM, "W^X");
+	/*
+	 * When the "MMAP" protection is on and shared libraries have
+	 * been already loaded (i.e. get_current_sara_mmap_blocked
+	 * returns true), this function must not allow:
+	 *    - new executable allocations
+	 *    - new non-executable allocations that may become
+	 *      executable bypassing the "MPROTECT" restriction;
+	 *      the "MPROTECT" protection will prevent a non-executable
+	 *      area to became executable only if it has the
+	 *      "VM_MAYWRITE" flag on.
+	 */
+	if (sara_wxp_flags & SARA_WXP_MMAP &&
+	    (vm_flags & VM_EXEC ||
+	     (!(vm_flags & VM_MAYWRITE) && (vm_flags & VM_MAYEXEC))) &&
+	    get_current_sara_mmap_blocked())
+		sara_warn_or_return(EPERM, "executable mmap");
+
+	return 0;
+}
+
+static int sara_file_mprotect(struct vm_area_struct *vma,
+				unsigned long reqprot,
+				unsigned long prot)
+{
+	u16 sara_wxp_flags;
+
+	if (!sara_enabled || !wxprot_enabled)
+		return 0;
+
+	if (current->in_execve)
+		sara_wxp_flags = get_current_sara_execve_flags();
+	else
+		sara_wxp_flags = get_current_sara_wxp_flags();
+
+	/*
+	 * vmas that may have been writable at some time in the past
+	 * (i.e. have the VM_MAYWRITE flag on) shouldn't be allowed
+	 * to be marked executable, unless they already are.
+	 */
+	if (sara_wxp_flags & SARA_WXP_MPROTECT &&
+	    prot & PROT_EXEC &&
+	    !(vma->vm_flags & VM_EXEC) &&
+	    vma->vm_flags & VM_MAYWRITE) {
+		/*
+		 * If every MPROTECT flag is on and verbose reporting
+		 * isn't needed, skip checking where the vma points to.
+		 * Otherwise check if it points to a file mapping,
+		 * to heap, to stack or to anywhere else.
+		 */
+		if ((sara_wxp_flags & SARA_WXP_MPROTECT) == SARA_WXP_MPROTECT &&
+		    !(sara_wxp_flags & SARA_WXP_COMPLAIN) &&
+		    !(sara_wxp_flags & SARA_WXP_VERBOSE))
+			return -EACCES;
+		else if (vma->vm_file) {
+			if (sara_wxp_flags & SARA_WXP_OTHER)
+				sara_warn_or_return(EACCES,
+						    "mprotect on file mmap");
+		} else if (vma->vm_start >= vma->vm_mm->start_brk &&
+			vma->vm_end <= vma->vm_mm->brk) {
+			if (sara_wxp_flags & SARA_WXP_HEAP)
+				sara_warn_or_return(EACCES,
+						    "mprotect on heap");
+		} else if ((vma->vm_start <= vma->vm_mm->start_stack &&
+			    vma->vm_end >= vma->vm_mm->start_stack) ||
+			   vma_is_stack_for_current(vma)) {
+			if (sara_wxp_flags & SARA_WXP_STACK)
+				sara_warn_or_return(EACCES,
+						    "mprotect on stack");
+		} else if (sara_wxp_flags & SARA_WXP_OTHER)
+			sara_warn_or_return(EACCES,
+					    "mprotect on anon mmap");
+	}
+
+	/*
+	 * If "W xor X" is active for the current thread
+	 * VM_EXEC and VM_WRITE can't be turned on at
+	 * the same time, unless they already are.
+	 */
+	if (sara_wxp_flags & SARA_WXP_WXORX &&
+	    prot & PROT_EXEC &&
+	    prot & PROT_WRITE &&
+	    (!(vma->vm_flags & VM_EXEC) ||
+	     !(vma->vm_flags & VM_WRITE)))
+		sara_warn_or_return(EACCES, "W^X");
+
+	/*
+	 * If the dynamic loader marks the "relro section" as
+	 * read-only then it has finished loading shared libraries
+	 * and, if the SARA_WXP_MMAP flag is on, new executable
+	 * mmaps will be blocked from now on.
+	 */
+	if (vma->vm_flags & VM_WRITE &&
+	    !(prot & PROT_WRITE) &&
+	    is_relro_page(vma))
+		get_current_sara_mmap_blocked() = true;
+
+	return 0;
+}
+
+static struct security_hook_list wxprot_hooks[] __ro_after_init = {
+	LSM_HOOK_INIT(bprm_set_creds, sara_bprm_set_creds),
+	LSM_HOOK_INIT(check_vmflags, sara_check_vmflags),
+	LSM_HOOK_INIT(file_mprotect, sara_file_mprotect),
+};
+
+struct binary_config_header {
+	char magic[8];
+	__le32 version;
+	__le32 rules_size;
+	char hash[SARA_CONFIG_HASH_LEN];
+} __packed;
+
+struct binary_config_rule {
+	__le16 path_len;
+	__le16 flags;
+	u8 exact;
+} __packed;
+
+static void config_free(struct wxprot_config_container *data)
+{
+	int i;
+
+	for (i = 0; i < data->rules_size; ++i)
+		kfree(data->rules[i].path);
+	kvfree(data->rules);
+	kfree(data);
+}
+
+static int config_load(const char *buf, size_t buf_len)
+{
+	int ret;
+	int i;
+	int path_len;
+	size_t inc;
+	size_t last_path_len = SARA_PATH_MAX;
+	bool last_exact = true;
+	const char *pos;
+	struct wxprot_config_container *new;
+	struct binary_config_header *h;
+	struct binary_config_rule *r;
+
+	ret = -EINVAL;
+	if (unlikely(buf_len < sizeof(*h)))
+		goto out;
+
+	h = (struct binary_config_header *) buf;
+	pos = buf + sizeof(*h);
+
+	ret = -EINVAL;
+	if (unlikely(memcmp(h->magic, "SARAWXPR", 8) != 0))
+		goto out;
+	if (unlikely(le32_to_cpu(h->version) != wxprot_config_version))
+		goto out;
+
+	ret = -ENOMEM;
+	new = kmalloc(sizeof(*new), GFP_KERNEL);
+	if (unlikely(new == NULL))
+		goto out;
+	kref_init(&new->refcount);
+	new->rules_size = le32_to_cpu(h->rules_size);
+	BUILD_BUG_ON(sizeof(new->hash) != sizeof(h->hash));
+	memcpy(new->hash, h->hash, sizeof(new->hash));
+	if (unlikely(new->rules_size == 0)) {
+		new->rules = NULL;
+		goto replace;
+	}
+
+	ret = -ENOMEM;
+	new->rules = sara_kvcalloc(new->rules_size,
+				   sizeof(*new->rules));
+	if (unlikely(new->rules == NULL))
+		goto out_new;
+	for (i = 0; i < new->rules_size; ++i) {
+		r = (struct binary_config_rule *) pos;
+		pos += sizeof(*r);
+		inc = pos-buf;
+		path_len = le16_to_cpu(r->path_len);
+		new->rules[i].flags = le16_to_cpu(r->flags);
+		new->rules[i].exact = r->exact;
+
+		ret = -EINVAL;
+		if (unlikely(inc + path_len > buf_len))
+			goto out_rules;
+		if (unlikely(path_len > last_path_len))
+			goto out_rules;
+		if (unlikely((int) new->rules[i].exact != 0 &&
+			     (int) new->rules[i].exact != 1))
+			goto out_rules;
+		if (unlikely(path_len == last_path_len &&
+			     new->rules[i].exact &&
+			     !last_exact))
+			goto out_rules;
+		if (!are_flags_valid(new->rules[i].flags))
+			goto out_rules;
+
+		ret = -ENOMEM;
+		new->rules[i].path = kmalloc(path_len+1, GFP_KERNEL);
+		if (unlikely(new->rules[i].path == NULL))
+			goto out_rules;
+		memcpy(new->rules[i].path, pos, path_len);
+		new->rules[i].path[path_len] = '\0';
+		if (i > 0 &&
+		    unlikely(new->rules[i].exact == new->rules[i-1].exact &&
+			     strcmp(new->rules[i].path,
+				    new->rules[i-1].path) == 0))
+			goto out_rules;
+		pos += path_len;
+		last_path_len = path_len;
+		last_exact = new->rules[i].exact;
+	}
+	new->buf_len = (size_t) (pos-buf);
+
+replace:
+	SARA_CONFIG_REPLACE(wxprot_config,
+			    new,
+			    config_free,
+			    &wxprot_config_lock);
+	pr_notice("WXP: new rules loaded.\n");
+	return 0;
+
+out_rules:
+	for (i = 0; i < new->rules_size; ++i)
+		kfree(new->rules[i].path);
+	kvfree(new->rules);
+out_new:
+	kfree(new);
+out:
+	pr_notice("WXP: failed to load rules.\n");
+	return ret;
+}
+
+static ssize_t config_dump(char **buf)
+{
+	int i;
+	ssize_t ret;
+	size_t buf_len;
+	char *pos;
+	char *mybuf;
+	u16 path_len;
+	int rulen;
+	struct wxprot_config_container *c;
+	struct wxprot_rule *rc;
+	struct binary_config_header *h;
+	struct binary_config_rule *r;
+
+	ret = -ENOMEM;
+	SARA_CONFIG_GET(c, wxprot_config);
+	buf_len = c->buf_len;
+	mybuf = sara_kvmalloc(buf_len);
+	if (unlikely(mybuf == NULL))
+		goto out;
+	rulen = c->rules_size;
+	h = (struct binary_config_header *) mybuf;
+	memcpy(h->magic, "SARAWXPR", 8);
+	h->version = cpu_to_le32(SARA_WXPROT_CONFIG_VERSION);
+	h->rules_size = cpu_to_le32(rulen);
+	BUILD_BUG_ON(sizeof(c->hash) != sizeof(h->hash));
+	memcpy(h->hash, c->hash, sizeof(h->hash));
+	pos = mybuf + sizeof(*h);
+	for (i = 0; i < rulen; ++i) {
+		r = (struct binary_config_rule *) pos;
+		pos += sizeof(*r);
+		if (buf_len < (pos - mybuf))
+			goto out;
+		rc = &c->rules[i];
+		r->flags = cpu_to_le16(rc->flags);
+		r->exact = (u8) rc->exact;
+		path_len = strlen(rc->path);
+		r->path_len = cpu_to_le16(path_len);
+		if (buf_len < ((pos - mybuf) + path_len))
+			goto out;
+		memcpy(pos, rc->path, path_len);
+		pos += path_len;
+	}
+	ret = (ssize_t) (pos - mybuf);
+	*buf = mybuf;
+out:
+	SARA_CONFIG_PUT(c, config_free);
+	return ret;
+}
+
+static int config_hash(char **buf)
+{
+	int ret;
+	struct wxprot_config_container *config;
+
+	ret = -ENOMEM;
+	*buf = kzalloc(sizeof(config->hash), GFP_KERNEL);
+	if (unlikely(*buf == NULL))
+		goto out;
+
+	SARA_CONFIG_GET_RCU(config, wxprot_config);
+	memcpy(*buf, config->hash, sizeof(config->hash));
+	SARA_CONFIG_PUT_RCU(config);
+
+	ret = 0;
+out:
+	return ret;
+}
+
+static DEFINE_SARA_SECFS_BOOL_FLAG(wxprot_enabled_data,
+				   wxprot_enabled);
+
+static struct sara_secfs_fptrs fptrs __ro_after_init = {
+	.load = config_load,
+	.dump = config_dump,
+	.hash = config_hash,
+};
+
+static const struct sara_secfs_node wxprot_fs[] __initconst = {
+	{
+		.name = "enabled",
+		.type = SARA_SECFS_BOOL,
+		.data = (void *) &wxprot_enabled_data,
+	},
+	{
+		.name = "version",
+		.type = SARA_SECFS_READONLY_INT,
+		.data = (int *) &wxprot_config_version,
+	},
+	{
+		.name = "default_flags",
+		.type = SARA_SECFS_READONLY_INT,
+		.data = &default_flags,
+	},
+	{
+		.name = "emutramp_available",
+		.type = SARA_SECFS_READONLY_INT,
+		.data = (int *) &wxprot_emutramp,
+	},
+	{
+		.name = ".load",
+		.type = SARA_SECFS_CONFIG_LOAD,
+		.data = &fptrs,
+	},
+	{
+		.name = ".dump",
+		.type = SARA_SECFS_CONFIG_DUMP,
+		.data = &fptrs,
+	},
+	{
+		.name = "hash",
+		.type = SARA_SECFS_CONFIG_HASH,
+		.data = &fptrs,
+	},
+};
+
+
+int __init sara_wxprot_init(void)
+{
+	int ret;
+	struct wxprot_config_container *tmpc = NULL;
+
+	ret = -EINVAL;
+	if (!are_flags_valid(default_flags))
+		goto out_fail;
+	ret = -ENOMEM;
+	tmpc = kzalloc(sizeof(*tmpc), GFP_KERNEL);
+	if (unlikely(tmpc == NULL))
+		goto out_fail;
+	tmpc->buf_len = sizeof(struct binary_config_header);
+	kref_init(&tmpc->refcount);
+	wxprot_config = (struct wxprot_config_container __rcu *) tmpc;
+	ret = sara_secfs_subtree_register("wxprot",
+					  wxprot_fs,
+					  ARRAY_SIZE(wxprot_fs));
+	if (unlikely(ret))
+		goto out_fail;
+	security_add_hooks(wxprot_hooks, ARRAY_SIZE(wxprot_hooks), "sara");
+	return 0;
+
+out_fail:
+	kfree(tmpc);
+	return ret;
+}
+
+#endif /* CONFIG_SECURITY_SARA_WXPROT */
-- 
1.9.1