php-src/sapi/fuzzer/fuzzer-execute-common.h

/*
   +----------------------------------------------------------------------+
   | Copyright (c) The PHP Group                                          |
   +----------------------------------------------------------------------+
   | This source file is subject to version 3.01 of the PHP license,      |
   | that is bundled with this package in the file LICENSE, and is        |
   | available through the world-wide-web at the following url:           |
   | https://www.php.net/license/3_01.txt                                 |
   | If you did not receive a copy of the PHP license and are unable to   |
   | obtain it through the world-wide-web, please send a note to          |
   | license@php.net so we can mail you a copy immediately.               |
   +----------------------------------------------------------------------+
   | Authors: Nikita Popov <nikic@php.net>                                |
   +----------------------------------------------------------------------+
 */

#include <main/php.h>

#if defined(__FreeBSD__)
# include <sys/sysctl.h>
#endif

#include "fuzzer.h"
#include "fuzzer-sapi.h"
#include "zend_exceptions.h"

#define FILE_NAME "/tmp/fuzzer.php"
#define MAX_STEPS 1000
#define MAX_SIZE (8 * 1024)
#define ZEND_VM_ENTER_BIT 1ULL

static uint32_t steps_left;
static bool bailed_out = false;

/* Because the fuzzer is always compiled with clang,
 * we can assume that we don't use global registers / hybrid VM. */
typedef zend_op *(ZEND_FASTCALL *opcode_handler_t)(zend_execute_data *, const zend_op *);

static zend_always_inline void fuzzer_bailout(void) {
	bailed_out = true;
	zend_bailout();
}

static zend_always_inline void fuzzer_step(void) {
	if (--steps_left == 0) {
		/* Reset steps before bailing out, so code running after bailout (e.g. in
		 * destructors) will get another MAX_STEPS, rather than UINT32_MAX steps. */
		steps_left = MAX_STEPS;
		fuzzer_bailout();
	}
}

static void (*orig_execute_ex)(zend_execute_data *execute_data);

static void fuzzer_execute_ex(zend_execute_data *execute_data) {

#ifdef ZEND_CHECK_STACK_LIMIT
	if (UNEXPECTED(zend_call_stack_overflowed(EG(stack_limit)))) {
		zend_call_stack_size_error();
		/* No opline was executed before exception */
		EG(opline_before_exception) = NULL;
		/* Fall through to handle exception below. */
	}
#endif /* ZEND_CHECK_STACK_LIMIT */

	const zend_op *opline = EX(opline);

	while (1) {
		fuzzer_step();
		opline = ((opcode_handler_t) opline->handler)(execute_data, opline);
		if ((uintptr_t) opline & ZEND_VM_ENTER_BIT) {
			opline = (const zend_op *) ((uintptr_t) opline & ~ZEND_VM_ENTER_BIT);
			if (opline) {
				execute_data = EG(current_execute_data);
			} else {
				return;
			}
		}
	}
}

static zend_op_array *(*orig_compile_string)(
		zend_string *source_string, const char *filename, zend_compile_position position);

static zend_op_array *fuzzer_compile_string(
		zend_string *str, const char *filename, zend_compile_position position) {
	if (ZSTR_LEN(str) > MAX_SIZE) {
		/* Avoid compiling huge inputs via eval(). */
		fuzzer_bailout();
	}

	return orig_compile_string(str, filename, position);
}

static void (*orig_execute_internal)(zend_execute_data *execute_data, zval *return_value);

static void fuzzer_execute_internal(zend_execute_data *execute_data, zval *return_value) {
	fuzzer_step();

	uint32_t num_args = ZEND_CALL_NUM_ARGS(execute_data);
	for (uint32_t i = 0; i < num_args; i++) {
		/* Some internal functions like preg_replace() may be slow on large inputs.
		 * Limit the maximum size of string inputs. */
		zval *arg = ZEND_CALL_VAR_NUM(execute_data, i);
		if (Z_TYPE_P(arg) == IS_STRING && Z_STRLEN_P(arg) > MAX_SIZE) {
			fuzzer_bailout();
		}
	}

	orig_execute_internal(execute_data, return_value);
}

static void fuzzer_init_php_for_execute(const char *extra_ini) {
	/* Compilation will often trigger fatal errors.
	 * Use tracked allocation mode to avoid leaks in that case. */
	putenv("USE_TRACKED_ALLOC=1");

	/* Just like other SAPIs, ignore SIGPIPEs. */
	signal(SIGPIPE, SIG_IGN);

	fuzzer_init_php(extra_ini);

	orig_execute_ex = zend_execute_ex;
	zend_execute_ex = fuzzer_execute_ex;
	orig_execute_internal = zend_execute_internal ? zend_execute_internal : execute_internal;
	zend_execute_internal = fuzzer_execute_internal;
	orig_compile_string = zend_compile_string;
	zend_compile_string = fuzzer_compile_string;
}

ZEND_ATTRIBUTE_UNUSED static void create_file(void) {
	/* For opcache_invalidate() to work, the dummy file name used for fuzzing needs to
	 * actually exist. */
	FILE *f = fopen(FILE_NAME, "w");
	fclose(f);
}

ZEND_ATTRIBUTE_UNUSED static void opcache_invalidate(void) {
	steps_left = MAX_STEPS;
	zend_exception_save();
	zval retval, args[2];
	zend_function *fn = zend_hash_str_find_ptr(CG(function_table), ZEND_STRL("opcache_invalidate"));
	ZEND_ASSERT(fn != NULL);

	ZVAL_STRING(&args[0], FILE_NAME);
	ZVAL_TRUE(&args[1]);
	zend_call_known_function(fn, NULL, NULL, &retval, 2, args, NULL);
	ZEND_ASSERT(Z_TYPE(retval) == IS_TRUE);
	zval_ptr_dtor(&args[0]);
	zval_ptr_dtor(&retval);
	zend_exception_restore();
}