24 files changed, 725 insertions, 22 deletions

diff --git a/arch/Kconfig b/arch/Kconfig
index 11d349561ece..659bdd079277 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -383,6 +383,24 @@ config GCC_PLUGIN_SANCOV
 	  gcc-4.5 on). It is based on the commit "Add fuzzing coverage support"
 	  by Dmitry Vyukov <dvyukov@google.com>.
 
+config GCC_PLUGIN_LATENT_ENTROPY
+	bool "Generate some entropy during boot and runtime"
+	depends on GCC_PLUGINS
+	help
+	  By saying Y here the kernel will instrument some kernel code to
+	  extract some entropy from both original and artificially created
+	  program state.  This will help especially embedded systems where
+	  there is little 'natural' source of entropy normally.  The cost
+	  is some slowdown of the boot process (about 0.5%) and fork and
+	  irq processing.
+
+	  Note that entropy extracted this way is not cryptographically
+	  secure!
+
+	  This plugin was ported from grsecurity/PaX. More information at:
+	   * https://grsecurity.net/
+	   * https://pax.grsecurity.net/
+
 config HAVE_CC_STACKPROTECTOR
 	bool
 	help
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index 6913f6725ce1..1925341dbb9c 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -14,6 +14,11 @@ CFLAGS_prom_init.o      += -fPIC
 CFLAGS_btext.o		+= -fPIC
 endif
 
+CFLAGS_cputable.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
+CFLAGS_init.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
+CFLAGS_btext.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
+CFLAGS_prom.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
+
 ifdef CONFIG_FUNCTION_TRACER
 # Do not trace early boot code
 CFLAGS_REMOVE_cputable.o = -mno-sched-epilog $(CC_FLAGS_FTRACE)
diff --git a/block/blk-softirq.c b/block/blk-softirq.c
index 96631e6a22b9..06cf9807f49a 100644
--- a/block/blk-softirq.c
+++ b/block/blk-softirq.c
@@ -18,7 +18,7 @@ static DEFINE_PER_CPU(struct list_head, blk_cpu_done);
  * Softirq action handler - move entries to local list and loop over them
  * while passing them to the queue registered handler.
  */
-static void blk_done_softirq(struct softirq_action *h)
+static __latent_entropy void blk_done_softirq(struct softirq_action *h)
 {
 	struct list_head *cpu_list, local_list;
 
diff --git a/drivers/char/random.c b/drivers/char/random.c
index d131e152c8ce..d6876d506220 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -479,8 +479,8 @@ static ssize_t _extract_entropy(struct entropy_store *r, void *buf,
 
 static void crng_reseed(struct crng_state *crng, struct entropy_store *r);
 static void push_to_pool(struct work_struct *work);
-static __u32 input_pool_data[INPUT_POOL_WORDS];
-static __u32 blocking_pool_data[OUTPUT_POOL_WORDS];
+static __u32 input_pool_data[INPUT_POOL_WORDS] __latent_entropy;
+static __u32 blocking_pool_data[OUTPUT_POOL_WORDS] __latent_entropy;
 
 static struct entropy_store input_pool = {
 	.poolinfo = &poolinfo_table[0],
diff --git a/fs/namespace.c b/fs/namespace.c
index 58aca9c931ac..e6c234b1a645 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2824,6 +2824,7 @@ static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns)
 	return new_ns;
 }
 
+__latent_entropy
 struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,
 		struct user_namespace *user_ns, struct fs_struct *new_fs)
 {
diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index 573c5a18908f..432f5c97e18f 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -188,6 +188,13 @@
 #endif /* GCC_VERSION >= 40300 */
 
 #if GCC_VERSION >= 40500
+
+#ifndef __CHECKER__
+#ifdef LATENT_ENTROPY_PLUGIN
+#define __latent_entropy __attribute__((latent_entropy))
+#endif
+#endif
+
 /*
  * Mark a position in code as unreachable.  This can be used to
  * suppress control flow warnings after asm blocks that transfer
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index f1bfa15b6f9b..cf0fa5d86059 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -429,6 +429,10 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
 # define __attribute_const__	/* unimplemented */
 #endif
 
+#ifndef __latent_entropy
+# define __latent_entropy
+#endif
+
 /*
  * Tell gcc if a function is cold. The compiler will assume any path
  * directly leading to the call is unlikely.
diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
index aca2a6a1d035..6e84b2cae6ad 100644
--- a/include/linux/fdtable.h
+++ b/include/linux/fdtable.h
@@ -105,7 +105,7 @@ struct files_struct *get_files_struct(struct task_struct *);
 void put_files_struct(struct files_struct *fs);
 void reset_files_struct(struct files_struct *);
 int unshare_files(struct files_struct **);
-struct files_struct *dup_fd(struct files_struct *, int *);
+struct files_struct *dup_fd(struct files_struct *, int *) __latent_entropy;
 void do_close_on_exec(struct files_struct *);
 int iterate_fd(struct files_struct *, unsigned,
 		int (*)(const void *, struct file *, unsigned),
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 1dbf52f9c24b..e0341af6950e 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -437,7 +437,7 @@ extern void disk_flush_events(struct gendisk *disk, unsigned int mask);
 extern unsigned int disk_clear_events(struct gendisk *disk, unsigned int mask);
 
 /* drivers/char/random.c */
-extern void add_disk_randomness(struct gendisk *disk);
+extern void add_disk_randomness(struct gendisk *disk) __latent_entropy;
 extern void rand_initialize_disk(struct gendisk *disk);
 
 static inline sector_t get_start_sect(struct block_device *bdev)
diff --git a/include/linux/init.h b/include/linux/init.h
index 024a0b5b3ed0..e30104ceb86d 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -39,7 +39,7 @@
 
 /* These are for everybody (although not all archs will actually
    discard it in modules) */
-#define __init		__section(.init.text) __cold notrace
+#define __init		__section(.init.text) __cold notrace __latent_entropy
 #define __initdata	__section(.init.data)
 #define __initconst	__section(.init.rodata)
 #define __exitdata	__section(.exit.data)
@@ -75,7 +75,8 @@
 #define __exit          __section(.exit.text) __exitused __cold notrace
 
 /* Used for MEMORY_HOTPLUG */
-#define __meminit        __section(.meminit.text) __cold notrace
+#define __meminit        __section(.meminit.text) __cold notrace \
+						  __latent_entropy
 #define __meminitdata    __section(.meminit.data)
 #define __meminitconst   __section(.meminit.rodata)
 #define __memexit        __section(.memexit.text) __exitused __cold notrace
diff --git a/include/linux/random.h b/include/linux/random.h
index f7bb7a355cf7..7bd2403e4fef 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -18,9 +18,20 @@ struct random_ready_callback {
 };
 
 extern void add_device_randomness(const void *, unsigned int);
+
+#if defined(CONFIG_GCC_PLUGIN_LATENT_ENTROPY) && !defined(__CHECKER__)
+static inline void add_latent_entropy(void)
+{
+	add_device_randomness((const void *)&latent_entropy,
+			      sizeof(latent_entropy));
+}
+#else
+static inline void add_latent_entropy(void) {}
+#endif
+
 extern void add_input_randomness(unsigned int type, unsigned int code,
-				 unsigned int value);
-extern void add_interrupt_randomness(int irq, int irq_flags);
+				 unsigned int value) __latent_entropy;
+extern void add_interrupt_randomness(int irq, int irq_flags) __latent_entropy;
 
 extern void get_random_bytes(void *buf, int nbytes);
 extern int add_random_ready_callback(struct random_ready_callback *rdy);
diff --git a/init/main.c b/init/main.c
index a8a58e2794a5..2858be732f6d 100644
--- a/init/main.c
+++ b/init/main.c
@@ -789,6 +789,7 @@ int __init_or_module do_one_initcall(initcall_t fn)
 	}
 	WARN(msgbuf[0], "initcall %pF returned with %s\n", fn, msgbuf);
 
+	add_latent_entropy();
 	return ret;
 }
 
diff --git a/kernel/fork.c b/kernel/fork.c
index 6d42242485cb..623259fc794d 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -547,7 +547,8 @@ free_tsk:
 }
 
 #ifdef CONFIG_MMU
-static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
+static __latent_entropy int dup_mmap(struct mm_struct *mm,
+					struct mm_struct *oldmm)
 {
 	struct vm_area_struct *mpnt, *tmp, *prev, **pprev;
 	struct rb_node **rb_link, *rb_parent;
@@ -1441,7 +1442,8 @@ init_task_pid(struct task_struct *task, enum pid_type type, struct pid *pid)
  * parts of the process environment (as per the clone
  * flags). The actual kick-off is left to the caller.
  */
-static struct task_struct *copy_process(unsigned long clone_flags,
+static __latent_entropy struct task_struct *copy_process(
+					unsigned long clone_flags,
 					unsigned long stack_start,
 					unsigned long stack_size,
 					int __user *child_tidptr,
@@ -1926,6 +1928,7 @@ long _do_fork(unsigned long clone_flags,
 
 	p = copy_process(clone_flags, stack_start, stack_size,
 			 child_tidptr, NULL, trace, tls, NUMA_NO_NODE);
+	add_latent_entropy();
 	/*
 	 * Do this prior waking up the new thread - the thread pointer
 	 * might get invalid after that point, if the thread exits quickly.
diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
index 944b1b491ed8..1898559e6b60 100644
--- a/kernel/rcu/tiny.c
+++ b/kernel/rcu/tiny.c
@@ -170,7 +170,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 				      false));
 }
 
-static void rcu_process_callbacks(struct softirq_action *unused)
+static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
 {
 	__rcu_process_callbacks(&rcu_sched_ctrlblk);
 	__rcu_process_callbacks(&rcu_bh_ctrlblk);
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 7e2e03879c2e..69a5611a7e7c 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3013,7 +3013,7 @@ __rcu_process_callbacks(struct rcu_state *rsp)
 /*
  * Do RCU core processing for the current CPU.
  */
-static void rcu_process_callbacks(struct softirq_action *unused)
+static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
 {
 	struct rcu_state *rsp;
 
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 502e95a6e927..2d4ad72f8f3c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8522,7 +8522,7 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) { }
  * run_rebalance_domains is triggered when needed from the scheduler tick.
  * Also triggered for nohz idle balancing (with nohz_balancing_kick set).
  */
-static void run_rebalance_domains(struct softirq_action *h)
+static __latent_entropy void run_rebalance_domains(struct softirq_action *h)
 {
 	struct rq *this_rq = this_rq();
 	enum cpu_idle_type idle = this_rq->idle_balance ?
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 66762645f9e8..1bf81ef91375 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -496,7 +496,7 @@ void __tasklet_hi_schedule_first(struct tasklet_struct *t)
 }
 EXPORT_SYMBOL(__tasklet_hi_schedule_first);
 
-static void tasklet_action(struct softirq_action *a)
+static __latent_entropy void tasklet_action(struct softirq_action *a)
 {
 	struct tasklet_struct *list;
 
@@ -532,7 +532,7 @@ static void tasklet_action(struct softirq_action *a)
 	}
 }
 
-static void tasklet_hi_action(struct softirq_action *a)
+static __latent_entropy void tasklet_hi_action(struct softirq_action *a)
 {
 	struct tasklet_struct *list;
 
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 32bf6f75a8fe..2d47980a1bc4 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1633,7 +1633,7 @@ static inline void __run_timers(struct timer_base *base)
 /*
  * This function runs timers and the timer-tq in bottom half context.
  */
-static void run_timer_softirq(struct softirq_action *h)
+static __latent_entropy void run_timer_softirq(struct softirq_action *h)
 {
 	struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]);
 
diff --git a/lib/irq_poll.c b/lib/irq_poll.c
index 2be55692aa43..1d6565e81030 100644
--- a/lib/irq_poll.c
+++ b/lib/irq_poll.c
@@ -74,7 +74,7 @@ void irq_poll_complete(struct irq_poll *iop)
 }
 EXPORT_SYMBOL(irq_poll_complete);
 
-static void irq_poll_softirq(struct softirq_action *h)
+static void __latent_entropy irq_poll_softirq(struct softirq_action *h)
 {
 	struct list_head *list = this_cpu_ptr(&blk_cpu_iopoll);
 	int rearm = 0, budget = irq_poll_budget;
diff --git a/lib/random32.c b/lib/random32.c
index 915982b304bb..fa594b1140e6 100644
--- a/lib/random32.c
+++ b/lib/random32.c
@@ -47,7 +47,7 @@ static inline void prandom_state_selftest(void)
 }
 #endif
 
-static DEFINE_PER_CPU(struct rnd_state, net_rand_state);
+static DEFINE_PER_CPU(struct rnd_state, net_rand_state) __latent_entropy;
 
 /**
  *	prandom_u32_state - seeded pseudo-random number generator.
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ca423cc20b59..2b3bf6767d54 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -91,6 +91,11 @@ EXPORT_PER_CPU_SYMBOL(_numa_mem_);
 int _node_numa_mem_[MAX_NUMNODES];
 #endif
 
+#ifdef CONFIG_GCC_PLUGIN_LATENT_ENTROPY
+volatile u64 latent_entropy __latent_entropy;
+EXPORT_SYMBOL(latent_entropy);
+#endif
+
 /*
  * Array of node states.
  */
diff --git a/net/core/dev.c b/net/core/dev.c
index f1fe26f66458..4bc19a164ba5 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3845,7 +3845,7 @@ int netif_rx_ni(struct sk_buff *skb)
 }
 EXPORT_SYMBOL(netif_rx_ni);
 
-static void net_tx_action(struct softirq_action *h)
+static __latent_entropy void net_tx_action(struct softirq_action *h)
 {
 	struct softnet_data *sd = this_cpu_ptr(&softnet_data);
 
@@ -5198,7 +5198,7 @@ out_unlock:
 	return work;
 }
 
-static void net_rx_action(struct softirq_action *h)
+static __latent_entropy void net_rx_action(struct softirq_action *h)
 {
 	struct softnet_data *sd = this_cpu_ptr(&softnet_data);
 	unsigned long time_limit = jiffies + 2;
diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins
index 61f0e6db909b..060d2cb373db 100644
--- a/scripts/Makefile.gcc-plugins
+++ b/scripts/Makefile.gcc-plugins
@@ -6,6 +6,12 @@ ifdef CONFIG_GCC_PLUGINS
 
   gcc-plugin-$(CONFIG_GCC_PLUGIN_CYC_COMPLEXITY)	+= cyc_complexity_plugin.so
 
+  gcc-plugin-$(CONFIG_GCC_PLUGIN_LATENT_ENTROPY)	+= latent_entropy_plugin.so
+  gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_LATENT_ENTROPY)	+= -DLATENT_ENTROPY_PLUGIN
+  ifdef CONFIG_PAX_LATENT_ENTROPY
+    DISABLE_LATENT_ENTROPY_PLUGIN			+= -fplugin-arg-latent_entropy_plugin-disable
+  endif
+
   ifdef CONFIG_GCC_PLUGIN_SANCOV
     ifeq ($(CFLAGS_KCOV),)
       # It is needed because of the gcc-plugin.sh and gcc version checks.
@@ -21,7 +27,8 @@ ifdef CONFIG_GCC_PLUGINS
 
   GCC_PLUGINS_CFLAGS := $(strip $(addprefix -fplugin=$(objtree)/scripts/gcc-plugins/, $(gcc-plugin-y)) $(gcc-plugin-cflags-y))
 
-  export PLUGINCC GCC_PLUGINS_CFLAGS GCC_PLUGIN GCC_PLUGIN_SUBDIR SANCOV_PLUGIN
+  export PLUGINCC GCC_PLUGINS_CFLAGS GCC_PLUGIN GCC_PLUGIN_SUBDIR
+  export SANCOV_PLUGIN DISABLE_LATENT_ENTROPY_PLUGIN
 
   ifneq ($(PLUGINCC),)
     # SANCOV_PLUGIN can be only in CFLAGS_KCOV because avoid duplication.
diff --git a/scripts/gcc-plugins/latent_entropy_plugin.c b/scripts/gcc-plugins/latent_entropy_plugin.c
new file mode 100644
index 000000000000..ff1939b804ae
--- /dev/null
+++ b/scripts/gcc-plugins/latent_entropy_plugin.c
@@ -0,0 +1,640 @@
+/*
+ * Copyright 2012-2016 by the PaX Team <pageexec@freemail.hu>
+ * Copyright 2016 by Emese Revfy <re.emese@gmail.com>
+ * Licensed under the GPL v2
+ *
+ * Note: the choice of the license means that the compilation process is
+ *       NOT 'eligible' as defined by gcc's library exception to the GPL v3,
+ *       but for the kernel it doesn't matter since it doesn't link against
+ *       any of the gcc libraries
+ *
+ * This gcc plugin helps generate a little bit of entropy from program state,
+ * used throughout the uptime of the kernel. Here is an instrumentation example:
+ *
+ * before:
+ * void __latent_entropy test(int argc, char *argv[])
+ * {
+ *	if (argc <= 1)
+ *		printf("%s: no command arguments :(\n", *argv);
+ *	else
+ *		printf("%s: %d command arguments!\n", *argv, args - 1);
+ * }
+ *
+ * after:
+ * void __latent_entropy test(int argc, char *argv[])
+ * {
+ *	// latent_entropy_execute() 1.
+ *	unsigned long local_entropy;
+ *	// init_local_entropy() 1.
+ *	void *local_entropy_frameaddr;
+ *	// init_local_entropy() 3.
+ *	unsigned long tmp_latent_entropy;
+ *
+ *	// init_local_entropy() 2.
+ *	local_entropy_frameaddr = __builtin_frame_address(0);
+ *	local_entropy = (unsigned long) local_entropy_frameaddr;
+ *
+ *	// init_local_entropy() 4.
+ *	tmp_latent_entropy = latent_entropy;
+ *	// init_local_entropy() 5.
+ *	local_entropy ^= tmp_latent_entropy;
+ *
+ *	// latent_entropy_execute() 3.
+ *	if (argc <= 1) {
+ *		// perturb_local_entropy()
+ *		local_entropy += 4623067384293424948;
+ *		printf("%s: no command arguments :(\n", *argv);
+ *		// perturb_local_entropy()
+ *	} else {
+ *		local_entropy ^= 3896280633962944730;
+ *		printf("%s: %d command arguments!\n", *argv, args - 1);
+ *	}
+ *
+ *	// latent_entropy_execute() 4.
+ *	tmp_latent_entropy = rol(tmp_latent_entropy, local_entropy);
+ *	latent_entropy = tmp_latent_entropy;
+ * }
+ *
+ * TODO:
+ * - add ipa pass to identify not explicitly marked candidate functions
+ * - mix in more program state (function arguments/return values,
+ *   loop variables, etc)
+ * - more instrumentation control via attribute parameters
+ *
+ * BUGS:
+ * - none known
+ *
+ * Options:
+ * -fplugin-arg-latent_entropy_plugin-disable
+ *
+ * Attribute: __attribute__((latent_entropy))
+ *  The latent_entropy gcc attribute can be only on functions and variables.
+ *  If it is on a function then the plugin will instrument it. If the attribute
+ *  is on a variable then the plugin will initialize it with a random value.
+ *  The variable must be an integer, an integer array type or a structure
+ *  with integer fields.
+ */
+
+#include "gcc-common.h"
+
+int plugin_is_GPL_compatible;
+
+static GTY(()) tree latent_entropy_decl;
+
+static struct plugin_info latent_entropy_plugin_info = {
+	.version	= "201606141920vanilla",
+	.help		= "disable\tturn off latent entropy instrumentation\n",
+};
+
+static unsigned HOST_WIDE_INT seed;
+/*
+ * get_random_seed() (this is a GCC function) generates the seed.
+ * This is a simple random generator without any cryptographic security because
+ * the entropy doesn't come from here.
+ */
+static unsigned HOST_WIDE_INT get_random_const(void)
+{
+	unsigned int i;
+	unsigned HOST_WIDE_INT ret = 0;
+
+	for (i = 0; i < 8 * sizeof(ret); i++) {
+		ret = (ret << 1) | (seed & 1);
+		seed >>= 1;
+		if (ret & 1)
+			seed ^= 0xD800000000000000ULL;
+	}
+
+	return ret;
+}
+
+static tree tree_get_random_const(tree type)
+{
+	unsigned long long mask;
+
+	mask = 1ULL << (TREE_INT_CST_LOW(TYPE_SIZE(type)) - 1);
+	mask = 2 * (mask - 1) + 1;
+
+	if (TYPE_UNSIGNED(type))
+		return build_int_cstu(type, mask & get_random_const());
+	return build_int_cst(type, mask & get_random_const());
+}
+
+static tree handle_latent_entropy_attribute(tree *node, tree name,
+						tree args __unused,
+						int flags __unused,
+						bool *no_add_attrs)
+{
+	tree type;
+#if BUILDING_GCC_VERSION <= 4007
+	VEC(constructor_elt, gc) *vals;
+#else
+	vec<constructor_elt, va_gc> *vals;
+#endif
+
+	switch (TREE_CODE(*node)) {
+	default:
+		*no_add_attrs = true;
+		error("%qE attribute only applies to functions and variables",
+			name);
+		break;
+
+	case VAR_DECL:
+		if (DECL_INITIAL(*node)) {
+			*no_add_attrs = true;
+			error("variable %qD with %qE attribute must not be initialized",
+				*node, name);
+			break;
+		}
+
+		if (!TREE_STATIC(*node)) {
+			*no_add_attrs = true;
+			error("variable %qD with %qE attribute must not be local",
+				*node, name);
+			break;
+		}
+
+		type = TREE_TYPE(*node);
+		switch (TREE_CODE(type)) {
+		default:
+			*no_add_attrs = true;
+			error("variable %qD with %qE attribute must be an integer or a fixed length integer array type or a fixed sized structure with integer fields",
+				*node, name);
+			break;
+
+		case RECORD_TYPE: {
+			tree fld, lst = TYPE_FIELDS(type);
+			unsigned int nelt = 0;
+
+			for (fld = lst; fld; nelt++, fld = TREE_CHAIN(fld)) {
+				tree fieldtype;
+
+				fieldtype = TREE_TYPE(fld);
+				if (TREE_CODE(fieldtype) == INTEGER_TYPE)
+					continue;
+
+				*no_add_attrs = true;
+				error("structure variable %qD with %qE attribute has a non-integer field %qE",
+					*node, name, fld);
+				break;
+			}
+
+			if (fld)
+				break;
+
+#if BUILDING_GCC_VERSION <= 4007
+			vals = VEC_alloc(constructor_elt, gc, nelt);
+#else
+			vec_alloc(vals, nelt);
+#endif
+
+			for (fld = lst; fld; fld = TREE_CHAIN(fld)) {
+				tree random_const, fld_t = TREE_TYPE(fld);
+
+				random_const = tree_get_random_const(fld_t);
+				CONSTRUCTOR_APPEND_ELT(vals, fld, random_const);
+			}
+
+			/* Initialize the fields with random constants */
+			DECL_INITIAL(*node) = build_constructor(type, vals);
+			break;
+		}
+
+		/* Initialize the variable with a random constant */
+		case INTEGER_TYPE:
+			DECL_INITIAL(*node) = tree_get_random_const(type);
+			break;
+
+		case ARRAY_TYPE: {
+			tree elt_type, array_size, elt_size;
+			unsigned int i, nelt;
+			HOST_WIDE_INT array_size_int, elt_size_int;
+
+			elt_type = TREE_TYPE(type);
+			elt_size = TYPE_SIZE_UNIT(TREE_TYPE(type));
+			array_size = TYPE_SIZE_UNIT(type);
+
+			if (TREE_CODE(elt_type) != INTEGER_TYPE || !array_size
+				|| TREE_CODE(array_size) != INTEGER_CST) {
+				*no_add_attrs = true;
+				error("array variable %qD with %qE attribute must be a fixed length integer array type",
+					*node, name);
+				break;
+			}
+
+			array_size_int = TREE_INT_CST_LOW(array_size);
+			elt_size_int = TREE_INT_CST_LOW(elt_size);
+			nelt = array_size_int / elt_size_int;
+
+#if BUILDING_GCC_VERSION <= 4007
+			vals = VEC_alloc(constructor_elt, gc, nelt);
+#else
+			vec_alloc(vals, nelt);
+#endif
+
+			for (i = 0; i < nelt; i++) {
+				tree cst = size_int(i);
+				tree rand_cst = tree_get_random_const(elt_type);
+
+				CONSTRUCTOR_APPEND_ELT(vals, cst, rand_cst);
+			}
+
+			/*
+			 * Initialize the elements of the array with random
+			 * constants
+			 */
+			DECL_INITIAL(*node) = build_constructor(type, vals);
+			break;
+		}
+		}
+		break;
+
+	case FUNCTION_DECL:
+		break;
+	}
+
+	return NULL_TREE;
+}
+
+static struct attribute_spec latent_entropy_attr = {
+	.name				= "latent_entropy",
+	.min_length			= 0,
+	.max_length			= 0,
+	.decl_required			= true,
+	.type_required			= false,
+	.function_type_required		= false,
+	.handler			= handle_latent_entropy_attribute,
+#if BUILDING_GCC_VERSION >= 4007
+	.affects_type_identity		= false
+#endif
+};
+
+static void register_attributes(void *event_data __unused, void *data __unused)
+{
+	register_attribute(&latent_entropy_attr);
+}
+
+static bool latent_entropy_gate(void)
+{
+	tree list;
+
+	/* don't bother with noreturn functions for now */
+	if (TREE_THIS_VOLATILE(current_function_decl))
+		return false;
+
+	/* gcc-4.5 doesn't discover some trivial noreturn functions */
+	if (EDGE_COUNT(EXIT_BLOCK_PTR_FOR_FN(cfun)->preds) == 0)
+		return false;
+
+	list = DECL_ATTRIBUTES(current_function_decl);
+	return lookup_attribute("latent_entropy", list) != NULL_TREE;
+}
+
+static tree create_var(tree type, const char *name)
+{
+	tree var;
+
+	var = create_tmp_var(type, name);
+	add_referenced_var(var);
+	mark_sym_for_renaming(var);
+	return var;
+}
+
+/*
+ * Set up the next operation and its constant operand to use in the latent
+ * entropy PRNG. When RHS is specified, the request is for perturbing the
+ * local latent entropy variable, otherwise it is for perturbing the global
+ * latent entropy variable where the two operands are already given by the
+ * local and global latent entropy variables themselves.
+ *
+ * The operation is one of add/xor/rol when instrumenting the local entropy
+ * variable and one of add/xor when perturbing the global entropy variable.
+ * Rotation is not used for the latter case because it would transmit less
+ * entropy to the global variable than the other two operations.
+ */
+static enum tree_code get_op(tree *rhs)
+{
+	static enum tree_code op;
+	unsigned HOST_WIDE_INT random_const;
+
+	random_const = get_random_const();
+
+	switch (op) {
+	case BIT_XOR_EXPR:
+		op = PLUS_EXPR;
+		break;
+
+	case PLUS_EXPR:
+		if (rhs) {
+			op = LROTATE_EXPR;
+			/*
+			 * This code limits the value of random_const to
+			 * the size of a wide int for the rotation
+			 */
+			random_const &= HOST_BITS_PER_WIDE_INT - 1;
+			break;
+		}
+
+	case LROTATE_EXPR:
+	default:
+		op = BIT_XOR_EXPR;
+		break;
+	}
+	if (rhs)
+		*rhs = build_int_cstu(unsigned_intDI_type_node, random_const);
+	return op;
+}
+
+static gimple create_assign(enum tree_code code, tree lhs, tree op1,
+				tree op2)
+{
+	return gimple_build_assign_with_ops(code, lhs, op1, op2);
+}
+
+static void perturb_local_entropy(basic_block bb, tree local_entropy)
+{
+	gimple_stmt_iterator gsi;
+	gimple assign;
+	tree rhs;
+	enum tree_code op;
+
+	op = get_op(&rhs);
+	assign = create_assign(op, local_entropy, local_entropy, rhs);
+	gsi = gsi_after_labels(bb);
+	gsi_insert_before(&gsi, assign, GSI_NEW_STMT);
+	update_stmt(assign);
+}
+
+static void __perturb_latent_entropy(gimple_stmt_iterator *gsi,
+					tree local_entropy)
+{
+	gimple assign;
+	tree temp;
+	enum tree_code op;
+
+	/* 1. create temporary copy of latent_entropy */
+	temp = create_var(unsigned_intDI_type_node, "tmp_latent_entropy");
+
+	/* 2. read... */
+	add_referenced_var(latent_entropy_decl);
+	mark_sym_for_renaming(latent_entropy_decl);
+	assign = gimple_build_assign(temp, latent_entropy_decl);
+	gsi_insert_before(gsi, assign, GSI_NEW_STMT);
+	update_stmt(assign);
+
+	/* 3. ...modify... */
+	op = get_op(NULL);
+	assign = create_assign(op, temp, temp, local_entropy);
+	gsi_insert_after(gsi, assign, GSI_NEW_STMT);
+	update_stmt(assign);
+
+	/* 4. ...write latent_entropy */
+	assign = gimple_build_assign(latent_entropy_decl, temp);
+	gsi_insert_after(gsi, assign, GSI_NEW_STMT);
+	update_stmt(assign);
+}
+
+static bool handle_tail_calls(basic_block bb, tree local_entropy)
+{
+	gimple_stmt_iterator gsi;
+
+	for (gsi = gsi_start_bb(bb); !gsi_end_p(gsi); gsi_next(&gsi)) {
+		gcall *call;
+		gimple stmt = gsi_stmt(gsi);
+
+		if (!is_gimple_call(stmt))
+			continue;
+
+		call = as_a_gcall(stmt);
+		if (!gimple_call_tail_p(call))
+			continue;
+
+		__perturb_latent_entropy(&gsi, local_entropy);
+		return true;
+	}
+
+	return false;
+}
+
+static void perturb_latent_entropy(tree local_entropy)
+{
+	edge_iterator ei;
+	edge e, last_bb_e;
+	basic_block last_bb;
+
+	gcc_assert(single_pred_p(EXIT_BLOCK_PTR_FOR_FN(cfun)));
+	last_bb_e = single_pred_edge(EXIT_BLOCK_PTR_FOR_FN(cfun));
+
+	FOR_EACH_EDGE(e, ei, last_bb_e->src->preds) {
+		if (ENTRY_BLOCK_PTR_FOR_FN(cfun) == e->src)
+			continue;
+		if (EXIT_BLOCK_PTR_FOR_FN(cfun) == e->src)
+			continue;
+
+		handle_tail_calls(e->src, local_entropy);
+	}
+
+	last_bb = single_pred(EXIT_BLOCK_PTR_FOR_FN(cfun));
+	if (!handle_tail_calls(last_bb, local_entropy)) {
+		gimple_stmt_iterator gsi = gsi_last_bb(last_bb);
+
+		__perturb_latent_entropy(&gsi, local_entropy);
+	}
+}
+
+static void init_local_entropy(basic_block bb, tree local_entropy)
+{
+	gimple assign, call;
+	tree frame_addr, rand_const, tmp, fndecl, udi_frame_addr;
+	enum tree_code op;
+	unsigned HOST_WIDE_INT rand_cst;
+	gimple_stmt_iterator gsi = gsi_after_labels(bb);
+
+	/* 1. create local_entropy_frameaddr */
+	frame_addr = create_var(ptr_type_node, "local_entropy_frameaddr");
+
+	/* 2. local_entropy_frameaddr = __builtin_frame_address() */
+	fndecl = builtin_decl_implicit(BUILT_IN_FRAME_ADDRESS);
+	call = gimple_build_call(fndecl, 1, integer_zero_node);
+	gimple_call_set_lhs(call, frame_addr);
+	gsi_insert_before(&gsi, call, GSI_NEW_STMT);
+	update_stmt(call);
+
+	udi_frame_addr = fold_convert(unsigned_intDI_type_node, frame_addr);
+	assign = gimple_build_assign(local_entropy, udi_frame_addr);
+	gsi_insert_after(&gsi, assign, GSI_NEW_STMT);
+	update_stmt(assign);
+
+	/* 3. create temporary copy of latent_entropy */
+	tmp = create_var(unsigned_intDI_type_node, "tmp_latent_entropy");
+
+	/* 4. read the global entropy variable into local entropy */
+	add_referenced_var(latent_entropy_decl);
+	mark_sym_for_renaming(latent_entropy_decl);
+	assign = gimple_build_assign(tmp, latent_entropy_decl);
+	gsi_insert_after(&gsi, assign, GSI_NEW_STMT);
+	update_stmt(assign);
+
+	/* 5. mix local_entropy_frameaddr into local entropy */
+	assign = create_assign(BIT_XOR_EXPR, local_entropy, local_entropy, tmp);
+	gsi_insert_after(&gsi, assign, GSI_NEW_STMT);
+	update_stmt(assign);
+
+	rand_cst = get_random_const();
+	rand_const = build_int_cstu(unsigned_intDI_type_node, rand_cst);
+	op = get_op(NULL);
+	assign = create_assign(op, local_entropy, local_entropy, rand_const);
+	gsi_insert_after(&gsi, assign, GSI_NEW_STMT);
+	update_stmt(assign);
+}
+
+static bool create_latent_entropy_decl(void)
+{
+	varpool_node_ptr node;
+
+	if (latent_entropy_decl != NULL_TREE)
+		return true;
+
+	FOR_EACH_VARIABLE(node) {
+		tree name, var = NODE_DECL(node);
+
+		if (DECL_NAME_LENGTH(var) < sizeof("latent_entropy") - 1)
+			continue;
+
+		name = DECL_NAME(var);
+		if (strcmp(IDENTIFIER_POINTER(name), "latent_entropy"))
+			continue;
+
+		latent_entropy_decl = var;
+		break;
+	}
+
+	return latent_entropy_decl != NULL_TREE;
+}
+
+static unsigned int latent_entropy_execute(void)
+{
+	basic_block bb;
+	tree local_entropy;
+
+	if (!create_latent_entropy_decl())
+		return 0;
+
+	/* prepare for step 2 below */
+	gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
+	bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
+	if (!single_pred_p(bb)) {
+		split_edge(single_succ_edge(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
+		gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
+		bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
+	}
+
+	/* 1. create the local entropy variable */
+	local_entropy = create_var(unsigned_intDI_type_node, "local_entropy");
+
+	/* 2. initialize the local entropy variable */
+	init_local_entropy(bb, local_entropy);
+
+	bb = bb->next_bb;
+
+	/*
+	 * 3. instrument each BB with an operation on the
+	 *    local entropy variable
+	 */
+	while (bb != EXIT_BLOCK_PTR_FOR_FN(cfun)) {
+		perturb_local_entropy(bb, local_entropy);
+		bb = bb->next_bb;
+	};
+
+	/* 4. mix local entropy into the global entropy variable */
+	perturb_latent_entropy(local_entropy);
+	return 0;
+}
+
+static void latent_entropy_start_unit(void *gcc_data __unused,
+					void *user_data __unused)
+{
+	tree type, id;
+	int quals;
+
+	seed = get_random_seed(false);
+
+	if (in_lto_p)
+		return;
+
+	/* extern volatile u64 latent_entropy */
+	gcc_assert(TYPE_PRECISION(long_long_unsigned_type_node) == 64);
+	quals = TYPE_QUALS(long_long_unsigned_type_node) | TYPE_QUAL_VOLATILE;
+	type = build_qualified_type(long_long_unsigned_type_node, quals);
+	id = get_identifier("latent_entropy");
+	latent_entropy_decl = build_decl(UNKNOWN_LOCATION, VAR_DECL, id, type);
+
+	TREE_STATIC(latent_entropy_decl) = 1;
+	TREE_PUBLIC(latent_entropy_decl) = 1;
+	TREE_USED(latent_entropy_decl) = 1;
+	DECL_PRESERVE_P(latent_entropy_decl) = 1;
+	TREE_THIS_VOLATILE(latent_entropy_decl) = 1;
+	DECL_EXTERNAL(latent_entropy_decl) = 1;
+	DECL_ARTIFICIAL(latent_entropy_decl) = 1;
+	lang_hooks.decls.pushdecl(latent_entropy_decl);
+}
+
+#define PASS_NAME latent_entropy
+#define PROPERTIES_REQUIRED PROP_gimple_leh | PROP_cfg
+#define TODO_FLAGS_FINISH TODO_verify_ssa | TODO_verify_stmts | TODO_dump_func \
+	| TODO_update_ssa
+#include "gcc-generate-gimple-pass.h"
+
+int plugin_init(struct plugin_name_args *plugin_info,
+		struct plugin_gcc_version *version)
+{
+	bool enabled = true;
+	const char * const plugin_name = plugin_info->base_name;
+	const int argc = plugin_info->argc;
+	const struct plugin_argument * const argv = plugin_info->argv;
+	int i;
+
+	struct register_pass_info latent_entropy_pass_info;
+
+	latent_entropy_pass_info.pass		= make_latent_entropy_pass();
+	latent_entropy_pass_info.reference_pass_name		= "optimized";
+	latent_entropy_pass_info.ref_pass_instance_number	= 1;
+	latent_entropy_pass_info.pos_op		= PASS_POS_INSERT_BEFORE;
+	static const struct ggc_root_tab gt_ggc_r_gt_latent_entropy[] = {
+		{
+			.base = &latent_entropy_decl,
+			.nelt = 1,
+			.stride = sizeof(latent_entropy_decl),
+			.cb = &gt_ggc_mx_tree_node,
+			.pchw = &gt_pch_nx_tree_node
+		},
+		LAST_GGC_ROOT_TAB
+	};
+
+	if (!plugin_default_version_check(version, &gcc_version)) {
+		error(G_("incompatible gcc/plugin versions"));
+		return 1;
+	}
+
+	for (i = 0; i < argc; ++i) {
+		if (!(strcmp(argv[i].key, "disable"))) {
+			enabled = false;
+			continue;
+		}
+		error(G_("unkown option '-fplugin-arg-%s-%s'"), plugin_name, argv[i].key);
+	}
+
+	register_callback(plugin_name, PLUGIN_INFO, NULL,
+				&latent_entropy_plugin_info);
+	if (enabled) {
+		register_callback(plugin_name, PLUGIN_START_UNIT,
+					&latent_entropy_start_unit, NULL);
+		register_callback(plugin_name, PLUGIN_REGISTER_GGC_ROOTS,
+				  NULL, (void *)&gt_ggc_r_gt_latent_entropy);
+		register_callback(plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL,
+					&latent_entropy_pass_info);
+	}
+	register_callback(plugin_name, PLUGIN_ATTRIBUTES, register_attributes,
+				NULL);
+
+	return 0;
+}