cregit-Linux how code gets into the kernel

Release 4.15 scripts/gcc-plugins/randomize_layout_plugin.c

/*
 * Copyright 2014-2016 by Open Source Security, Inc., Brad Spengler <spender@grsecurity.net>
 *                   and PaX Team <pageexec@freemail.hu>
 * 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
 *
 * Usage:
 * $ # for 4.5/4.6/C based 4.7
 * $ gcc -I`gcc -print-file-name=plugin`/include -I`gcc -print-file-name=plugin`/include/c-family -fPIC -shared -O2 -o randomize_layout_plugin.so randomize_layout_plugin.c
 * $ # for C++ based 4.7/4.8+
 * $ g++ -I`g++ -print-file-name=plugin`/include -I`g++ -print-file-name=plugin`/include/c-family -fPIC -shared -O2 -o randomize_layout_plugin.so randomize_layout_plugin.c
 * $ gcc -fplugin=./randomize_layout_plugin.so test.c -O2
 */

#include "gcc-common.h"
#include "randomize_layout_seed.h"

#if BUILDING_GCC_MAJOR < 4 || (BUILDING_GCC_MAJOR == 4 && BUILDING_GCC_MINOR < 7)
#error "The RANDSTRUCT plugin requires GCC 4.7 or newer."
#endif


#define ORIG_TYPE_NAME(node) \
	(TYPE_NAME(TYPE_MAIN_VARIANT(node)) != NULL_TREE ? ((const unsigned char *)IDENTIFIER_POINTER(TYPE_NAME(TYPE_MAIN_VARIANT(node)))) : (const unsigned char *)"anonymous")


#define INFORM(loc, msg, ...)	inform(loc, "randstruct: " msg, ##__VA_ARGS__)

#define MISMATCH(loc, how, ...)	INFORM(loc, "casting between randomized structure pointer types (" how "): %qT and %qT\n", __VA_ARGS__)


__visible int plugin_is_GPL_compatible;


static int performance_mode;


static struct plugin_info randomize_layout_plugin_info = {
	.version	= "201402201816vanilla",
	.help		= "disable\t\t\tdo not activate plugin\n"
			  "performance-mode\tenable cacheline-aware layout randomization\n"
};


struct whitelist_entry {
	
const char *pathname;
	
const char *lhs;
	
const char *rhs;
};


static const struct whitelist_entry whitelist[] = {
	/* NIU overloads mapping with page struct */
	{ "drivers/net/ethernet/sun/niu.c", "page", "address_space" },
	/* unix_skb_parms via UNIXCB() buffer */
	{ "net/unix/af_unix.c", "unix_skb_parms", "char" },
	/* big_key payload.data struct splashing */
	{ "security/keys/big_key.c", "path", "void *" },
	/* walk struct security_hook_heads as an array of struct list_head */
	{ "security/security.c", "list_head", "security_hook_heads" },
	{ }
};

/* from old Linux dcache.h */

static inline unsigned long partial_name_hash(unsigned long c, unsigned long prevhash) { return (prevhash + (c << 4) + (c >> 4)) * 11; }

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static inline unsigned int name_hash(const unsigned char *name) { unsigned long hash = 0; unsigned int len = strlen((const char *)name); while (len--) hash = partial_name_hash(*name++, hash); return (unsigned int)hash; }

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static tree handle_randomize_layout_attr(tree *node, tree name, tree args, int flags, bool *no_add_attrs) { tree type; *no_add_attrs = true; if (TREE_CODE(*node) == FUNCTION_DECL) { error("%qE attribute does not apply to functions (%qF)", name, *node); return NULL_TREE; } if (TREE_CODE(*node) == PARM_DECL) { error("%qE attribute does not apply to function parameters (%qD)", name, *node); return NULL_TREE; } if (TREE_CODE(*node) == VAR_DECL) { error("%qE attribute does not apply to variables (%qD)", name, *node); return NULL_TREE; } if (TYPE_P(*node)) { type = *node; } else { gcc_assert(TREE_CODE(*node) == TYPE_DECL); type = TREE_TYPE(*node); } if (TREE_CODE(type) != RECORD_TYPE) { error("%qE attribute used on %qT applies to struct types only", name, type); return NULL_TREE; } if (lookup_attribute(IDENTIFIER_POINTER(name), TYPE_ATTRIBUTES(type))) { error("%qE attribute is already applied to the type %qT", name, type); return NULL_TREE; } *no_add_attrs = false; return NULL_TREE; }

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/* set on complete types that we don't need to inspect further at all */
static tree handle_randomize_considered_attr(tree *node, tree name, tree args, int flags, bool *no_add_attrs) { *no_add_attrs = false; return NULL_TREE; }

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/* * set on types that we've performed a shuffle on, to prevent re-shuffling * this does not preclude us from inspecting its fields for potential shuffles */
static tree handle_randomize_performed_attr(tree *node, tree name, tree args, int flags, bool *no_add_attrs) { *no_add_attrs = false; return NULL_TREE; }

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/* * 64bit variant of Bob Jenkins' public domain PRNG * 256 bits of internal state */ typedef unsigned long long u64; typedef struct ranctx { u64 a; u64 b; u64 c; u64 d; } ranctx; #define rot(x,k) (((x)<<(k))|((x)>>(64-(k))))
static u64 ranval(ranctx *x) { u64 e = x->a - rot(x->b, 7); x->a = x->b ^ rot(x->c, 13); x->b = x->c + rot(x->d, 37); x->c = x->d + e; x->d = e + x->a; return x->d; }

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static void raninit(ranctx *x, u64 *seed) { int i; x->a = seed[0]; x->b = seed[1]; x->c = seed[2]; x->d = seed[3]; for (i=0; i < 30; ++i) (void)ranval(x); }

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static u64 shuffle_seed[4]; struct partition_group { tree tree_start; unsigned long start; unsigned long length; };
static void partition_struct(tree *fields, unsigned long length, struct partition_group *size_groups, unsigned long *num_groups) { unsigned long i; unsigned long accum_size = 0; unsigned long accum_length = 0; unsigned long group_idx = 0; gcc_assert(length < INT_MAX); memset(size_groups, 0, sizeof(struct partition_group) * length); for (i = 0; i < length; i++) { if (size_groups[group_idx].tree_start == NULL_TREE) { size_groups[group_idx].tree_start = fields[i]; size_groups[group_idx].start = i; accum_length = 0; accum_size = 0; } accum_size += (unsigned long)int_size_in_bytes(TREE_TYPE(fields[i])); accum_length++; if (accum_size >= 64) { size_groups[group_idx].length = accum_length; accum_length = 0; group_idx++; } } if (size_groups[group_idx].tree_start != NULL_TREE && !size_groups[group_idx].length) { size_groups[group_idx].length = accum_length; group_idx++; } *num_groups = group_idx; }

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static void performance_shuffle(tree *newtree, unsigned long length, ranctx *prng_state) { unsigned long i, x; struct partition_group size_group[length]; unsigned long num_groups = 0; unsigned long randnum; partition_struct(newtree, length, (struct partition_group *)&size_group, &num_groups); for (i = num_groups - 1; i > 0; i--) { struct partition_group tmp; randnum = ranval(prng_state) % (i + 1); tmp = size_group[i]; size_group[i] = size_group[randnum]; size_group[randnum] = tmp; } for (x = 0; x < num_groups; x++) { for (i = size_group[x].start + size_group[x].length - 1; i > size_group[x].start; i--) { tree tmp; if (DECL_BIT_FIELD_TYPE(newtree[i])) continue; randnum = ranval(prng_state) % (i + 1); // we could handle this case differently if desired if (DECL_BIT_FIELD_TYPE(newtree[randnum])) continue; tmp = newtree[i]; newtree[i] = newtree[randnum]; newtree[randnum] = tmp; } } }

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static void full_shuffle(tree *newtree, unsigned long length, ranctx *prng_state) { unsigned long i, randnum; for (i = length - 1; i > 0; i--) { tree tmp; randnum = ranval(prng_state) % (i + 1); tmp = newtree[i]; newtree[i] = newtree[randnum]; newtree[randnum] = tmp; } }

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/* modern in-place Fisher-Yates shuffle */
static void shuffle(const_tree type, tree *newtree, unsigned long length) { unsigned long i; u64 seed[4]; ranctx prng_state; const unsigned char *structname; if (length == 0) return; gcc_assert(TREE_CODE(type) == RECORD_TYPE); structname = ORIG_TYPE_NAME(type); #ifdef __DEBUG_PLUGIN fprintf(stderr, "Shuffling struct %s %p\n", (const char *)structname, type); #ifdef __DEBUG_VERBOSE debug_tree((tree)type); #endif #endif for (i = 0; i < 4; i++) { seed[i] = shuffle_seed[i]; seed[i] ^= name_hash(structname); } raninit(&prng_state, (u64 *)&seed); if (performance_mode) performance_shuffle(newtree, length, &prng_state); else full_shuffle(newtree, length, &prng_state); }

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static bool is_flexible_array(const_tree field) { const_tree fieldtype; const_tree typesize; const_tree elemtype; const_tree elemsize; fieldtype = TREE_TYPE(field); typesize = TYPE_SIZE(fieldtype); if (TREE_CODE(fieldtype) != ARRAY_TYPE) return false; elemtype = TREE_TYPE(fieldtype); elemsize = TYPE_SIZE(elemtype); /* size of type is represented in bits */ if (typesize == NULL_TREE && TYPE_DOMAIN(fieldtype) != NULL_TREE && TYPE_MAX_VALUE(TYPE_DOMAIN(fieldtype)) == NULL_TREE) return true; if (typesize != NULL_TREE && (TREE_CONSTANT(typesize) && (!tree_to_uhwi(typesize) || tree_to_uhwi(typesize) == tree_to_uhwi(elemsize)))) return true; return false; }

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static int relayout_struct(tree type) { unsigned long num_fields = (unsigned long)list_length(TYPE_FIELDS(type)); unsigned long shuffle_length = num_fields; tree field; tree newtree[num_fields]; unsigned long i; tree list; tree variant; tree main_variant; expanded_location xloc; bool has_flexarray = false; if (TYPE_FIELDS(type) == NULL_TREE) return 0; if (num_fields < 2) return 0; gcc_assert(TREE_CODE(type) == RECORD_TYPE); gcc_assert(num_fields < INT_MAX); if (lookup_attribute("randomize_performed", TYPE_ATTRIBUTES(type)) || lookup_attribute("no_randomize_layout", TYPE_ATTRIBUTES(TYPE_MAIN_VARIANT(type)))) return 0; /* Workaround for 3rd-party VirtualBox source that we can't modify ourselves */ if (!strcmp((const char *)ORIG_TYPE_NAME(type), "INTNETTRUNKFACTORY") || !strcmp((const char *)ORIG_TYPE_NAME(type), "RAWPCIFACTORY")) return 0; /* throw out any structs in uapi */ xloc = expand_location(DECL_SOURCE_LOCATION(TYPE_FIELDS(type))); if (strstr(xloc.file, "/uapi/")) error(G_("attempted to randomize userland API struct %s"), ORIG_TYPE_NAME(type)); for (field = TYPE_FIELDS(type), i = 0; field; field = TREE_CHAIN(field), i++) { gcc_assert(TREE_CODE(field) == FIELD_DECL); newtree[i] = field; } /* * enforce that we don't randomize the layout of the last * element of a struct if it's a 0 or 1-length array * or a proper flexible array */ if (is_flexible_array(newtree[num_fields - 1])) { has_flexarray = true; shuffle_length--; } shuffle(type, (tree *)newtree, shuffle_length); /* * set up a bogus anonymous struct field designed to error out on unnamed struct initializers * as gcc provides no other way to detect such code */ list = make_node(FIELD_DECL); TREE_CHAIN(list) = newtree[0]; TREE_TYPE(list) = void_type_node; DECL_SIZE(list) = bitsize_zero_node; DECL_NONADDRESSABLE_P(list) = 1; DECL_FIELD_BIT_OFFSET(list) = bitsize_zero_node; DECL_SIZE_UNIT(list) = size_zero_node; DECL_FIELD_OFFSET(list) = size_zero_node; DECL_CONTEXT(list) = type; // to satisfy the constify plugin TREE_READONLY(list) = 1; for (i = 0; i < num_fields - 1; i++) TREE_CHAIN(newtree[i]) = newtree[i+1]; TREE_CHAIN(newtree[num_fields - 1]) = NULL_TREE; main_variant = TYPE_MAIN_VARIANT(type); for (variant = main_variant; variant; variant = TYPE_NEXT_VARIANT(variant)) { TYPE_FIELDS(variant) = list; TYPE_ATTRIBUTES(variant) = copy_list(TYPE_ATTRIBUTES(variant)); TYPE_ATTRIBUTES(variant) = tree_cons(get_identifier("randomize_performed"), NULL_TREE, TYPE_ATTRIBUTES(variant)); TYPE_ATTRIBUTES(variant) = tree_cons(get_identifier("designated_init"), NULL_TREE, TYPE_ATTRIBUTES(variant)); if (has_flexarray) TYPE_ATTRIBUTES(type) = tree_cons(get_identifier("has_flexarray"), NULL_TREE, TYPE_ATTRIBUTES(type)); } /* * force a re-layout of the main variant * the TYPE_SIZE for all variants will be recomputed * by finalize_type_size() */ TYPE_SIZE(main_variant) = NULL_TREE; layout_type(main_variant); gcc_assert(TYPE_SIZE(main_variant) != NULL_TREE); return 1; }

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/* from constify plugin */
static const_tree get_field_type(const_tree field) { return strip_array_types(TREE_TYPE(field)); }

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/* from constify plugin */
static bool is_fptr(const_tree fieldtype) { if (TREE_CODE(fieldtype) != POINTER_TYPE) return false; return TREE_CODE(TREE_TYPE(fieldtype)) == FUNCTION_TYPE; }

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/* derived from constify plugin */
static int is_pure_ops_struct(const_tree node) { const_tree field; gcc_assert(TREE_CODE(node) == RECORD_TYPE || TREE_CODE(node) == UNION_TYPE); for (field = TYPE_FIELDS(node); field; field = TREE_CHAIN(field)) { const_tree fieldtype = get_field_type(field); enum tree_code code = TREE_CODE(fieldtype); if (node == fieldtype) continue; if (!is_fptr(fieldtype)) return 0; if (code != RECORD_TYPE && code != UNION_TYPE) continue; if (!is_pure_ops_struct(fieldtype)) return 0; } return 1; }

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static void randomize_type(tree type) { tree variant; gcc_assert(TREE_CODE(type) == RECORD_TYPE); if (lookup_attribute("randomize_considered", TYPE_ATTRIBUTES(type))) return; if (lookup_attribute("randomize_layout", TYPE_ATTRIBUTES(TYPE_MAIN_VARIANT(type))) || is_pure_ops_struct(type)) relayout_struct(type); for (variant = TYPE_MAIN_VARIANT(type); variant; variant = TYPE_NEXT_VARIANT(variant)) { TYPE_ATTRIBUTES(type) = copy_list(TYPE_ATTRIBUTES(type)); TYPE_ATTRIBUTES(type) = tree_cons(get_identifier("randomize_considered"), NULL_TREE, TYPE_ATTRIBUTES(type)); } #ifdef __DEBUG_PLUGIN fprintf(stderr, "Marking randomize_considered on struct %s\n", ORIG_TYPE_NAME(type)); #ifdef __DEBUG_VERBOSE debug_tree(type); #endif #endif }

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static void update_decl_size(tree decl) { tree lastval, lastidx, field, init, type, flexsize; unsigned HOST_WIDE_INT len; type = TREE_TYPE(decl); if (!lookup_attribute("has_flexarray", TYPE_ATTRIBUTES(type))) return; init = DECL_INITIAL(decl); if (init == NULL_TREE || init == error_mark_node) return; if (TREE_CODE(init) != CONSTRUCTOR) return; len = CONSTRUCTOR_NELTS(init); if (!len) return; lastval = CONSTRUCTOR_ELT(init, CONSTRUCTOR_NELTS(init) - 1)->value; lastidx = CONSTRUCTOR_ELT(init, CONSTRUCTOR_NELTS(init) - 1)->index; for (field = TYPE_FIELDS(TREE_TYPE(decl)); TREE_CHAIN(field); field = TREE_CHAIN(field)) ; if (lastidx != field) return; if (TREE_CODE(lastval) != STRING_CST) { error("Only string constants are supported as initializers " "for randomized structures with flexible arrays"); return; } flexsize = bitsize_int(TREE_STRING_LENGTH(lastval) * tree_to_uhwi(TYPE_SIZE(TREE_TYPE(TREE_TYPE(lastval))))); DECL_SIZE(decl) = size_binop(PLUS_EXPR, TYPE_SIZE(type), flexsize); return; }

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static void randomize_layout_finish_decl(void *event_data, void *data) { tree decl = (tree)event_data; tree type; if (decl == NULL_TREE || decl == error_mark_node) return; type = TREE_TYPE(decl); if (TREE_CODE(decl) != VAR_DECL) return; if (TREE_CODE(type) != RECORD_TYPE && TREE_CODE(type) != UNION_TYPE) return; if (!lookup_attribute("randomize_performed", TYPE_ATTRIBUTES(type))) return; DECL_SIZE(decl) = 0; DECL_SIZE_UNIT(decl) = 0; SET_DECL_ALIGN(decl, 0); SET_DECL_MODE (decl, VOIDmode); SET_DECL_RTL(decl, 0); update_decl_size(decl); layout_decl(decl, 0); }

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static void finish_type(void *event_data, void *data) { tree type = (tree)event_data; if (type == NULL_TREE || type == error_mark_node) return; if (TREE_CODE(type) != RECORD_TYPE) return; if (TYPE_FIELDS(type) == NULL_TREE) return; if (lookup_attribute("randomize_considered", TYPE_ATTRIBUTES(type))) return; #ifdef __DEBUG_PLUGIN fprintf(stderr, "Calling randomize_type on %s\n", ORIG_TYPE_NAME(type)); #endif #ifdef __DEBUG_VERBOSE debug_tree(type); #endif randomize_type(type); return; }

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static struct attribute_spec randomize_layout_attr = { .name = "randomize_layout", // related to args .min_length = 0, .max_length = 0, .decl_required = false, // need type declaration .type_required = true, .function_type_required = false, .handler = handle_randomize_layout_attr, #if BUILDING_GCC_VERSION >= 4007 .affects_type_identity = true #endif }; static struct attribute_spec no_randomize_layout_attr = { .name = "no_randomize_layout", // related to args .min_length = 0, .max_length = 0, .decl_required = false, // need type declaration .type_required = true, .function_type_required = false, .handler = handle_randomize_layout_attr, #if BUILDING_GCC_VERSION >= 4007 .affects_type_identity = true #endif }; static struct