[PATCH v4 0/4] Introduce the latent_entropy gcc plugin

[PATCH v4 0/4] Introduce the latent_entropy gcc plugin

[Emese Revfy]

I would like to introduce the latent_entropy gcc plugin. This plugin
mitigates the problem of the kernel having too little entropy during and
after boot for generating crypto keys.

This plugin mixes random values into the latent_entropy global variable
in functions marked by the __latent_entropy attribute.
The value of this global variable is added to the kernel entropy pool
to increase the entropy.

It is a CII project supported by the Linux Foundation.

The latent_entropy plugin was ported from grsecurity/PaX originally written
by the PaX Team. You can find more about the plugin here:
https://grsecurity.net/pipermail/grsecurity/2012-July/001093.html

The plugin supports all gcc version from 4.5 to 6.0.

I do some changes above the PaX version. The important one is mixing
the stack pointer into the global variable too.
You can find more about the changes here:
https://github.com/ephox-gcc-plugins/latent_entropy

This patch set is based on the "Introduce GCC plugin infrastructure"
patch set (git/mmarek/kbuild.git#kbuild HEAD: 543c37cb165049c3be).

Emese Revfy (4):
 Add support for passing gcc plugin arguments
 Add the latent_entropy gcc plugin
 Mark functions with the latent_entropy attribute
 Add the extra_latent_entropy kernel parameter


Changes from v3:
  * Fix disabling latent_entropy on some powerpc files
    (Reported-by: Kees Cook <keescook@chromium.org>)
  * Truncate the lines into <= 80 columns to follow the kernel coding style
    (Suggested-by: Kees Cook <keescook@chromium.org>)

Changes from v2:
  * Moved the passing of gcc plugin arguments into a separate patch
    (Suggested-by: Kees Cook <keescook@chromium.org>)
  * Mix the global entropy variable with the stack pointer
    (latent_entropy_plugin.c)
  * Handle tail calls (latent_entropy_plugin.c)
  * Fix some indentation related warnings suggested by checkpatch.pl
    (latent_entropy_plugin.c)
  * Commented some latent_entropy plugin code
    (Suggested-by: Kees Cook <keescook@chromium.org>)

Changes from v1:
  * Remove unnecessary ifdefs
    (Suggested-by: Kees Cook <keescook@chromium.org>)
  * Separate the two definitions of add_latent_entropy()
    (Suggested-by: Kees Cook <keescook@chromium.org>)
  * Removed unnecessary global variable (latent_entropy_plugin.c)
  * About the latent_entropy gcc attribute (latent_entropy_plugin.c)
  * Measure the boot time performance impact of the latent_entropy plugin
    (arch/Kconfig)

---
 Documentation/kernel-parameters.txt         |   5 +
 arch/Kconfig                                |  23 +
 arch/powerpc/kernel/Makefile                |   4 +
 block/blk-softirq.c                         |   2 +-
 drivers/char/random.c                       |   6 +-
 fs/namespace.c                              |   1 +
 include/linux/compiler-gcc.h                |   7 +
 include/linux/compiler.h                    |   4 +
 include/linux/fdtable.h                     |   2 +-
 include/linux/genhd.h                       |   2 +-
 include/linux/init.h                        |   5 +-
 include/linux/random.h                      |  14 +-
 init/main.c                                 |   1 +
 kernel/fork.c                               |   7 +-
 kernel/rcu/tiny.c                           |   2 +-
 kernel/rcu/tree.c                           |   2 +-
 kernel/sched/fair.c                         |   2 +-
 kernel/softirq.c                            |   4 +-
 kernel/time/timer.c                         |   2 +-
 lib/irq_poll.c                              |   2 +-
 lib/random32.c                              |   2 +-
 mm/page_alloc.c                             |  31 ++
 net/core/dev.c                              |   4 +-
 scripts/Makefile.gcc-plugins                |  10 +-
 scripts/gcc-plugins/Makefile                |   1 +
 scripts/gcc-plugins/latent_entropy_plugin.c | 639 ++++++++++++++++++++++++++++
 26 files changed, 760 insertions(+), 24 deletions(-)

[PATCH v4 1/4] Add support for passing gcc plugin arguments

[Emese Revfy]

Signed-off-by: Emese Revfy <re.emese@gmail.com>
---
 scripts/Makefile.gcc-plugins | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins
index 5e22b60..da7f86c 100644
--- a/scripts/Makefile.gcc-plugins
+++ b/scripts/Makefile.gcc-plugins
@@ -19,7 +19,7 @@ ifdef CONFIG_GCC_PLUGINS
     endif
   endif
 
-  GCC_PLUGINS_CFLAGS := $(addprefix -fplugin=$(objtree)/scripts/gcc-plugins/, $(gcc-plugin-y))
+  GCC_PLUGINS_CFLAGS := $(strip $(addprefix -fplugin=$(objtree)/scripts/gcc-plugins/, $(gcc-plugin-y)) $(gcc-plugin-cflags-y))
 
   export PLUGINCC GCC_PLUGINS_CFLAGS GCC_PLUGIN SANCOV_PLUGIN
 
-- 
2.8.1

[PATCH v4 2/4] Add the latent_entropy gcc plugin

[Emese Revfy]

This plugin mitigates the problem of the kernel having too little entropy
during and after boot for generating crypto keys.

It creates a local variable in every marked function. The value of
this variable is modified by randomly chosen operations (add, xor and rol)
and random values (gcc generates them at compile time and the stack pointer
at runtime).
It depends on the control flow (e.g., loops, conditions).

Before the function returns the plugin writes this local variable
into the latent_entropy global variable. The value of this global variable
is added to the kernel entropy pool in do_one_initcall() and _do_fork().

Signed-off-by: Emese Revfy <re.emese@gmail.com>
---
 arch/Kconfig                                |  18 +
 arch/powerpc/kernel/Makefile                |   4 +
 include/linux/random.h                      |  10 +
 init/main.c                                 |   1 +
 kernel/fork.c                               |   1 +
 mm/page_alloc.c                             |   5 +
 scripts/Makefile.gcc-plugins                |   8 +-
 scripts/gcc-plugins/Makefile                |   1 +
 scripts/gcc-plugins/latent_entropy_plugin.c | 639 ++++++++++++++++++++++++++++
 9 files changed, 686 insertions(+), 1 deletion(-)
 create mode 100644 scripts/gcc-plugins/latent_entropy_plugin.c

diff --git a/arch/Kconfig b/arch/Kconfig
index 05f1e95..4b7cc2f 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -393,6 +393,24 @@ 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 2da380f..01935b8 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -15,6 +15,10 @@ CFLAGS_btext.o		+= -fPIC
 endif
 
 ifdef CONFIG_FUNCTION_TRACER
+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)
 # Do not trace early boot code
 CFLAGS_REMOVE_cputable.o = -mno-sched-epilog $(CC_FLAGS_FTRACE)
 CFLAGS_REMOVE_prom_init.o = -mno-sched-epilog $(CC_FLAGS_FTRACE)
diff --git a/include/linux/random.h b/include/linux/random.h
index e47e533..752e7df 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -18,6 +18,16 @@ 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);
diff --git a/init/main.c b/init/main.c
index 4c17fda..07e4174 100644
--- a/init/main.c
+++ b/init/main.c
@@ -781,6 +781,7 @@ 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 5c2c355..fd1b3c2 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1761,6 +1761,7 @@ 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/mm/page_alloc.c b/mm/page_alloc.c
index f8f3bfc..d10324e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1234,6 +1234,11 @@ static void __free_pages_ok(struct page *page, unsigned int order)
 	local_irq_restore(flags);
 }
 
+#ifdef CONFIG_GCC_PLUGIN_LATENT_ENTROPY
+volatile u64 latent_entropy;
+EXPORT_SYMBOL(latent_entropy);
+#endif
+
 static void __init __free_pages_boot_core(struct page *page, unsigned int order)
 {
 	unsigned int nr_pages = 1 << order;
diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins
index da7f86c..cd7902c 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 +27,7 @@ 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 SANCOV_PLUGIN
+  export PLUGINCC GCC_PLUGINS_CFLAGS GCC_PLUGIN SANCOV_PLUGIN DISABLE_LATENT_ENTROPY_PLUGIN
 
   ifeq ($(PLUGINCC),)
     ifneq ($(GCC_PLUGINS_CFLAGS),)
diff --git a/scripts/gcc-plugins/Makefile b/scripts/gcc-plugins/Makefile
index 88c8ec4..a3f8ca4a 100644
--- a/scripts/gcc-plugins/Makefile
+++ b/scripts/gcc-plugins/Makefile
@@ -23,5 +23,6 @@ always := $($(HOSTLIBS)-y)
 
 cyc_complexity_plugin-objs := cyc_complexity_plugin.o
 sancov_plugin-objs := sancov_plugin.o
+latent_entropy_plugin-objs := latent_entropy_plugin.o
 
 clean-files += *.so
diff --git a/scripts/gcc-plugins/latent_entropy_plugin.c b/scripts/gcc-plugins/latent_entropy_plugin.c
new file mode 100644
index 0000000..eb07b70
--- /dev/null
+++ b/scripts/gcc-plugins/latent_entropy_plugin.c
@@ -0,0 +1,639 @@
+/*
+ * 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[])
+ * {
+ *	printf("%u %s\n", argc, *argv);
+ * }
+ *
+ * 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.
+ *	local_entropy += 4623067384293424948;
+ *
+ *	printf("%u %s\n", argc, *argv);
+ *
+ *	// latent_entropy_execute() 4.
+ *	tmp_latent_entropy = rol(tmp_latent_entropy, local_entropy);
+ *	latent_entropy = tmp_latent_entropy;
+ * }
+ *
+ * It would look like this in C:
+ *
+ * unsigned long local_entropy = latent_entropy;
+ * local_entropy ^= 1234567890;
+ * local_entropy ^= (unsigned long)__builtin_frame_address(0);
+ * local_entropy += 9876543210;
+ * latent_entropy = rol(local_entropy, 1234509876);
+ *
+ * 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;
+
+	/* 2. initialize local entropy variable */
+	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;
+}
-- 
2.8.1

[PATCH v4 3/4] Mark functions with the latent_entropy attribute

[Emese Revfy]

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.

These functions have been selected because they are init functions or
are called at random times or they have variable loops.

Signed-off-by: Emese Revfy <re.emese@gmail.com>
---
 block/blk-softirq.c          | 2 +-
 drivers/char/random.c        | 6 +++---
 fs/namespace.c               | 1 +
 include/linux/compiler-gcc.h | 7 +++++++
 include/linux/compiler.h     | 4 ++++
 include/linux/fdtable.h      | 2 +-
 include/linux/genhd.h        | 2 +-
 include/linux/init.h         | 5 +++--
 include/linux/random.h       | 4 ++--
 kernel/fork.c                | 6 ++++--
 kernel/rcu/tiny.c            | 2 +-
 kernel/rcu/tree.c            | 2 +-
 kernel/sched/fair.c          | 2 +-
 kernel/softirq.c             | 4 ++--
 kernel/time/timer.c          | 2 +-
 lib/irq_poll.c               | 2 +-
 lib/random32.c               | 2 +-
 mm/page_alloc.c              | 2 +-
 net/core/dev.c               | 4 ++--
 19 files changed, 38 insertions(+), 23 deletions(-)

diff --git a/block/blk-softirq.c b/block/blk-softirq.c
index 53b1737..489eab8 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 0158d3b..6cca3ed 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -443,9 +443,9 @@ struct entropy_store {
 };
 
 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 nonblocking_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 __u32 nonblocking_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 4fb1691..0951eca 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2778,6 +2778,7 @@ 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 e294939..0ef8329 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 793c082..c65327b 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -425,6 +425,10 @@ 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 5295535..9852c7e 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 359a8e4..8736c1f 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -433,7 +433,7 @@ 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 aedb254..88646cb 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	__constsection(.init.rodata)
 #define __exitdata	__section(.exit.data)
@@ -92,7 +92,8 @@
 #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   __constsection(.meminit.rodata)
 #define __memexit        __section(.memexit.text) __exitused __cold notrace
diff --git a/include/linux/random.h b/include/linux/random.h
index 752e7df..d286d51 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -29,8 +29,8 @@ 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/kernel/fork.c b/kernel/fork.c
index fd1b3c2..8b1e313 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -406,7 +406,8 @@ 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;
@@ -1277,7 +1278,8 @@ 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,
diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
index 944b1b4..1898559 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 c7f1bc4..8821fce 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3004,7 +3004,7 @@ __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 218f8e8..cd745c2 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8205,7 +8205,7 @@ 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 17caf4b..34033fd 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -482,7 +482,7 @@ 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;
 
@@ -518,7 +518,7 @@ 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 3a95f97..6008e7ae 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1414,7 +1414,7 @@ void update_process_times(int user_tick)
 /*
  * 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 tvec_base *base = this_cpu_ptr(&tvec_bases);
 
diff --git a/lib/irq_poll.c b/lib/irq_poll.c
index 836f7db..63be749 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 510d1ce..722d2b6 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 d10324e..ffc4f4a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1235,7 +1235,7 @@ static void __free_pages_ok(struct page *page, unsigned int order)
 }
 
 #ifdef CONFIG_GCC_PLUGIN_LATENT_ENTROPY
-volatile u64 latent_entropy;
+volatile u64 latent_entropy __latent_entropy;
 EXPORT_SYMBOL(latent_entropy);
 #endif
 
diff --git a/net/core/dev.c b/net/core/dev.c
index 904ff43..723d3af 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3851,7 +3851,7 @@ 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);
 
@@ -5175,7 +5175,7 @@ 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;
-- 
2.8.1

[PATCH v4 4/4] Add the extra_latent_entropy kernel parameter

[Emese Revfy]

When extra_latent_entropy is passed on the kernel command line,
entropy will be extracted from up to the first 4GB of RAM while the
runtime memory allocator is being initialized.

Based on work created by the PaX Team.

Signed-off-by: Emese Revfy <re.emese@gmail.com>
---
 Documentation/kernel-parameters.txt |  5 +++++
 arch/Kconfig                        |  5 +++++
 mm/page_alloc.c                     | 26 ++++++++++++++++++++++++++
 3 files changed, 36 insertions(+)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 82b42c9..d870702 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2862,6 +2862,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			the specified number of seconds.  This is to be used if
 			your oopses keep scrolling off the screen.
 
+	extra_latent_entropy
+			Enable a very simple form of latent entropy extraction
+			from the first 4GB of memory as the bootmem allocator
+			passes the memory pages to the buddy allocator.
+
 	pcbit=		[HW,ISDN]
 
 	pcd.		[PARIDE]
diff --git a/arch/Kconfig b/arch/Kconfig
index 4b7cc2f..3374d50 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -404,6 +404,11 @@ config GCC_PLUGIN_LATENT_ENTROPY
 	  is some slowdown of the boot process (about 0.5%) and fork and
 	  irq processing.
 
+	  When extra_latent_entropy is passed on the kernel command line,
+	  entropy will be extracted from up to the first 4GB of RAM while the
+	  runtime memory allocator is being initialized. This costs even more
+	  slowdown of the boot process.
+
 	  Note that entropy extracted this way is not cryptographically
 	  secure!
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ffc4f4a..0a40c12 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -63,6 +63,7 @@
 #include <linux/sched/rt.h>
 #include <linux/page_owner.h>
 #include <linux/kthread.h>
+#include <linux/random.h>
 
 #include <asm/sections.h>
 #include <asm/tlbflush.h>
@@ -1234,6 +1235,15 @@ static void __free_pages_ok(struct page *page, unsigned int order)
 	local_irq_restore(flags);
 }
 
+bool __meminitdata extra_latent_entropy;
+
+static int __init setup_extra_latent_entropy(char *str)
+{
+	extra_latent_entropy = true;
+	return 0;
+}
+early_param("extra_latent_entropy", setup_extra_latent_entropy);
+
 #ifdef CONFIG_GCC_PLUGIN_LATENT_ENTROPY
 volatile u64 latent_entropy __latent_entropy;
 EXPORT_SYMBOL(latent_entropy);
@@ -1254,6 +1264,22 @@ static void __init __free_pages_boot_core(struct page *page, unsigned int order)
 	__ClearPageReserved(p);
 	set_page_count(p, 0);
 
+	if (extra_latent_entropy && !PageHighMem(page) &&
+		page_to_pfn(page) < 0x100000) {
+		u64 hash = 0;
+		size_t index, end = PAGE_SIZE * nr_pages / sizeof(hash);
+		const u64 *data = lowmem_page_address(page);
+
+		for (index = 0; index < end; index++)
+			hash ^= hash + data[index];
+#ifdef CONFIG_GCC_PLUGIN_LATENT_ENTROPY
+		latent_entropy ^= hash;
+		add_device_randomness((const void *)&latent_entropy, sizeof(latent_entropy));
+#else
+		add_device_randomness((const void *)&hash, sizeof(hash));
+#endif
+	}
+
 	page_zone(page)->managed_pages += nr_pages;
 	set_page_refcounted(page);
 	__free_pages(page, order);
-- 
2.8.1

Re: [PATCH v4 2/4] Add the latent_entropy gcc plugin

[Christoph Hellwig]

On Mon, Jun 20, 2016 at 08:41:19PM +0200, Emese Revfy wrote:
> --- /dev/null
> +++ b/scripts/gcc-plugins/latent_entropy_plugin.c
> @@ -0,0 +1,639 @@
> +/*
> + * 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

I remember we used to have architectures that actually linked against
libgcc.  Isn't that the case anymore?

Re: [PATCH v4 2/4] Add the latent_entropy gcc plugin

[Kees Cook]

On Tue, Jun 21, 2016 at 5:58 AM, Christoph Hellwig <hch@infradead.org> wrote:
> On Mon, Jun 20, 2016 at 08:41:19PM +0200, Emese Revfy wrote:
>> --- /dev/null
>> +++ b/scripts/gcc-plugins/latent_entropy_plugin.c
>> @@ -0,0 +1,639 @@
>> +/*
>> + * 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
>
> I remember we used to have architectures that actually linked against
> libgcc.  Isn't that the case anymore?

There are a few, but they don't (and won't) select HAVE_GCC_PLUGINS.

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security

Re: [PATCH v4 0/4] Introduce the latent_entropy gcc plugin

[Kees Cook]

On Mon, Jun 20, 2016 at 11:39 AM, Emese Revfy <re.emese@gmail.com> wrote:
> I would like to introduce the latent_entropy gcc plugin. This plugin
> mitigates the problem of the kernel having too little entropy during and
> after boot for generating crypto keys.
>
> This plugin mixes random values into the latent_entropy global variable
> in functions marked by the __latent_entropy attribute.
> The value of this global variable is added to the kernel entropy pool
> to increase the entropy.
>
> It is a CII project supported by the Linux Foundation.
>
> The latent_entropy plugin was ported from grsecurity/PaX originally written
> by the PaX Team. You can find more about the plugin here:
> https://grsecurity.net/pipermail/grsecurity/2012-July/001093.html
>
> The plugin supports all gcc version from 4.5 to 6.0.
>
> I do some changes above the PaX version. The important one is mixing
> the stack pointer into the global variable too.
> You can find more about the changes here:
> https://github.com/ephox-gcc-plugins/latent_entropy
>
> This patch set is based on the "Introduce GCC plugin infrastructure"
> patch set (git/mmarek/kbuild.git#kbuild HEAD: 543c37cb165049c3be).
>
> Emese Revfy (4):
>  Add support for passing gcc plugin arguments
>  Add the latent_entropy gcc plugin
>  Mark functions with the latent_entropy attribute
>  Add the extra_latent_entropy kernel parameter

Thanks! This looks good to me. I've adjusted some of the commit
message language for clarity and fixed a few other >80 lines that
stood out to me.

I've applied this to for-next/kspp and after I finish local build
testing, it should appear in linux-next.

Yay! :)

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security