mtag: tweak get_mtag_sval()

[smatch.git] / smatch_mtag.c

/*
 * Copyright (C) 2017 Oracle.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see http://www.gnu.org/copyleft/gpl.txt
 */

/*
 * One problem that I have is that it's really hard to track how pointers are
 * passed around.  For example, it would be nice to know that the probe() and
 * remove() functions get the same pci_dev pointer.  It would be good to know
 * what pointers we're passing to the open() and close() functions.  But that
 * information gets lost in a call tree full of function pointer calls.
 *
 * I think the first step is to start naming specific pointers.  So when a
 * pointer is allocated, then it gets a tag.  So calls to kmalloc() generate a
 * tag.  But we might not use that, because there might be a better name like
 * framebuffer_alloc(). The framebuffer_alloc() is interesting because there is
 * one per driver and it's passed around to all the file operations.
 *
 * Perhaps we could make a list of functions like framebuffer_alloc() which take
 * a size and say that those are the interesting alloc functions.
 *
 * Another place where we would maybe name the pointer is when they are passed
 * to the probe().  Because that's an important pointer, since there is one
 * per driver (sort of).
 *
 * My vision is that you could take a pointer and trace it back to a global.  So
 * I'm going to track that pointer_tag - 28 bytes takes you to another pointer
 * tag.  You could follow that one back and so on.  Also when we pass a pointer
 * to a function that would be recorded as sort of a link or path or something.
 *
 */

#include "smatch.h"
#include "smatch_slist.h"
#include "smatch_extra.h"

#include <openssl/md5.h>

static int my_id;

static mtag_t str_to_tag(const char *str)
{
        unsigned char c[MD5_DIGEST_LENGTH];
        unsigned long long *tag = (unsigned long long *)&c;
        MD5_CTX mdContext;
        int len;

        len = strlen(str);
        MD5_Init(&mdContext);
        MD5_Update(&mdContext, str, len);
        MD5_Final(c, &mdContext);

        *tag &= ~MTAG_ALIAS_BIT;
        *tag &= ~MTAG_OFFSET_MASK;

        return *tag;
}

const struct {
        const char *name;
        int size_arg;
} allocator_info[] = {
        { "kmalloc", 0 },
        { "kzalloc", 0 },
        { "devm_kmalloc", 1},
        { "devm_kzalloc", 1},
};

static bool is_mtag_call(struct expression *expr)
{
        struct expression *arg;
        int i;
        sval_t sval;

        if (expr->type != EXPR_CALL ||
            expr->fn->type != EXPR_SYMBOL ||
            !expr->fn->symbol)
                return false;

        for (i = 0; i < ARRAY_SIZE(allocator_info); i++) {
                if (strcmp(expr->fn->symbol->ident->name, allocator_info[i].name) == 0)
                        break;
        }
        if (i == ARRAY_SIZE(allocator_info))
                return false;

        arg = get_argument_from_call_expr(expr->args, allocator_info[i].size_arg);
        if (!get_implied_value(arg, &sval))
                return false;

        return true;
}

struct smatch_state *swap_mtag_return(struct expression *expr, struct smatch_state *state)
{
        struct expression *left, *right;
        char *left_name, *right_name;
        struct symbol *left_sym;
        struct range_list *rl;
        char buf[256];
        mtag_t tag;
        sval_t tag_sval;

        if (!expr || expr->type != EXPR_ASSIGNMENT || expr->op != '=')
                return state;

        if (!estate_rl(state) || strcmp(state->name, "0,4096-ptr_max") != 0)
                return state;

        left = strip_expr(expr->left);
        right = strip_expr(expr->right);

        if (!is_mtag_call(right))
                return state;

        left_name = expr_to_str_sym(left, &left_sym);
        if (!left_name || !left_sym)
                return state;
        right_name = expr_to_str(right);

        snprintf(buf, sizeof(buf), "%s %s %s %s", get_filename(), get_function(),
                 left_name, right_name);
        tag = str_to_tag(buf);
        tag_sval.type = estate_type(state);
        tag_sval.uvalue = tag;

        rl = rl_filter(estate_rl(state), valid_ptr_rl);
        rl = clone_rl(rl);
        add_range(&rl, tag_sval, tag_sval);

        sql_insert_mtag_about(tag, left_name, buf);

        free_string(left_name);
        free_string(right_name);

        return alloc_estate_rl(rl);
}

int get_string_mtag(struct expression *expr, mtag_t *tag)
{
        mtag_t xor;

        if (expr->type != EXPR_STRING || !expr->string)
                return 0;

        /* I was worried about collisions so I added a xor */
        xor = str_to_tag("__smatch string");
        *tag = str_to_tag(expr->string->data);
        *tag = *tag ^ xor;

        return 1;
}

int get_toplevel_mtag(struct symbol *sym, mtag_t *tag)
{
        char buf[256];

        if (!sym)
                return 0;

        if (!sym->ident ||
            !(sym->ctype.modifiers & MOD_TOPLEVEL))
                return 0;

        snprintf(buf, sizeof(buf), "%s %s",
                 (sym->ctype.modifiers & MOD_STATIC) ? get_filename() : "extern",
                 sym->ident->name);
        *tag = str_to_tag(buf);
        return 1;
}

static void global_variable(struct symbol *sym)
{
        mtag_t tag;

        if (!get_toplevel_mtag(sym, &tag))
                return;

        sql_insert_mtag_about(tag,
                              sym->ident->name,
                              (sym->ctype.modifiers & MOD_STATIC) ? get_filename() : "extern");
}

static int get_array_mtag_offset(struct expression *expr, mtag_t *tag, int *offset)
{
        struct expression *array, *offset_expr;
        struct symbol *type;
        sval_t sval;
        int start_offset;

        if (!is_array(expr))
                return 0;

        array = get_array_base(expr);
        if (!array)
                return 0;
        type = get_type(array);
        if (!type || type->type != SYM_ARRAY)
                return 0;
        type = get_real_base_type(type);
        if (!type_bytes(type))
                return 0;

        if (!expr_to_mtag_offset(array, tag, &start_offset))
                return 0;

        offset_expr = get_array_offset(expr);
        if (!get_value(offset_expr, &sval))
                return 0;
        *offset = start_offset + sval.value * type_bytes(type);

        return 1;
}

static int get_implied_mtag_offset(struct expression *expr, mtag_t *tag, int *offset)
{
        struct smatch_state *state;
        struct symbol *type;
        sval_t sval;

        type = get_type(expr);
        if (!type_is_ptr(type))
                return 0;
        state = get_extra_state(expr);
        if (!state || !estate_get_single_value(state, &sval) || sval.value == 0)
                return 0;

        *tag = sval.uvalue & ~MTAG_OFFSET_MASK;
        *offset = sval.uvalue & MTAG_OFFSET_MASK;
        return 1;
}

static int get_mtag_cnt;
int get_mtag(struct expression *expr, mtag_t *tag)
{
        int ret = 0;

        expr = strip_expr(expr);
        if (!expr)
                return 0;

        if (get_mtag_cnt > 0)
                return 0;

        get_mtag_cnt++;

        switch (expr->type) {
        case EXPR_STRING:
                if (get_string_mtag(expr, tag)) {
                        ret = 1;
                        goto dec_cnt;
                }
                break;
        case EXPR_SYMBOL:
                if (get_toplevel_mtag(expr->symbol, tag)) {
                        ret = 1;
                        goto dec_cnt;
                }
                break;
        }

dec_cnt:
        get_mtag_cnt--;
        return ret;
}

struct range_list *swap_mtag_seed(struct expression *expr, struct range_list *rl)
{
        char buf[256];
        char *name;
        sval_t sval;
        mtag_t tag;

        if (!rl_to_sval(rl, &sval))
                return rl;
        if (sval.type->type != SYM_PTR || sval.uvalue != MTAG_SEED)
                return rl;

        name = expr_to_str(expr);
        snprintf(buf, sizeof(buf), "%s %s %s", get_filename(), get_function(), name);
        free_string(name);
        tag = str_to_tag(buf);
        sval.value = tag;
        return alloc_rl(sval, sval);
}

int create_mtag_alias(mtag_t tag, struct expression *expr, mtag_t *new)
{
        char buf[256];
        int lines_from_start;
        char *str;

        /*
         * We need the alias to be unique.  It's not totally required that it
         * be the same from one DB build to then next, but it makes debugging
         * a bit simpler.
         *
         */

        if (!cur_func_sym)
                return 0;

        lines_from_start = expr->pos.line - cur_func_sym->pos.line;
        str = expr_to_str(expr);
        snprintf(buf, sizeof(buf), "%lld %d %s", tag, lines_from_start, str);
        free_string(str);

        *new = str_to_tag(buf);
        sql_insert_mtag_alias(tag, *new);

        return 1;
}

/*
 * The point of this function is to give you the mtag and the offset so
 * you can look up the data in the DB.  It takes an expression.
 *
 * So say you give it "foo->bar".  Then it would give you the offset of "bar"
 * and the implied value of "foo".  Or if you lookup "*foo" then the offset is
 * zero and we look up the implied value of "foo.  But if the expression is
 * foo, then if "foo" is a global variable, then we get the mtag and the offset
 * is zero.  If "foo" is a local variable, then there is nothing to look up in
 * the mtag_data table because that's handled by smatch_extra.c to this returns
 * false.
 *
 */
int expr_to_mtag_offset(struct expression *expr, mtag_t *tag, int *offset)
{
        *tag = 0;
        *offset = 0;

        expr = strip_expr(expr);
        if (!expr)
                return 0;

        if (is_array(expr))
                return get_array_mtag_offset(expr, tag, offset);

        if (expr->type == EXPR_PREOP && expr->op == '*') {
                expr = strip_expr(expr->unop);
                if (get_implied_mtag_offset(expr, tag, offset))
                        return 1;
        } else if (expr->type == EXPR_DEREF) {
                int next_offset;

                *offset = get_member_offset_from_deref(expr);
                if (*offset < 0)
                        return 0;
                expr = expr->deref;
                if (expr->type == EXPR_PREOP && expr->op == '*')
                        expr = strip_expr(expr->unop);

                if (get_implied_mtag_offset(expr, tag, &next_offset)) {
                        // FIXME:  look it up recursively?
                        if (next_offset)
                                return 0;
                        return 1;
                }
        }

        switch (expr->type) {
        case EXPR_STRING:
                return get_string_mtag(expr, tag);
        case EXPR_SYMBOL:
                return get_toplevel_mtag(expr->symbol, tag);
        }
        return 0;
}

/*
 * This function takes an address and returns an sval.  Let's take some
 * example things you might pass to it:
 * foo->bar:
 *   If we were only called from smatch_math, we wouldn't need to bother with
 *   this because it's already been looked up in smatch_extra.c but this is
 *   also called from other places so we have to check smatch_extra.c.
 * &foo
 *   If "foo" is global return the mtag for "foo".
 * &foo.bar
 *   If "foo" is global return the mtag for "foo" + the offset of ".bar".
 * It also handles string literals.
 *
 */
int get_mtag_sval(struct expression *expr, sval_t *sval)
{
        struct symbol *type;
        mtag_t tag;
        int offset = 0;

        if (bits_in_pointer != 64)
                return 0;

        expr = strip_expr(expr);

        type = get_type(expr);
        if (!type_is_ptr(type))
                return 0;
        /*
         * There are only three options:
         *
         * 1) An array address:
         *    p = array;
         * 2) An address like so:
         *    p = &my_struct->member;
         * 3) A pointer:
         *    p = pointer;
         *
         */

        if (expr->type == EXPR_STRING && get_string_mtag(expr, &tag))
                goto found;

        if (expr->type == EXPR_SYMBOL &&
            (type->type == SYM_ARRAY || type->type == SYM_FN) &&
            get_toplevel_mtag(expr->symbol, &tag))
                goto found;

        if (get_implied_mtag_offset(expr, &tag, &offset))
                goto found;

        if (expr->type != EXPR_PREOP || expr->op != '&')
                return 0;
        expr = strip_expr(expr->unop);

        if (!expr_to_mtag_offset(expr, &tag, &offset))
                return 0;
found:
        if (offset >= MTAG_OFFSET_MASK)
                return 0;

        sval->type = type;
        sval->uvalue = tag | offset;

        return 1;
}

void register_mtag(int id)
{
        my_id = id;


        /*
         * The mtag stuff only works on 64 systems because we store the
         * information in the pointer itself.
         * bit 63   : set for alias mtags
         * bit 62-12: mtag hash
         * bit 11-0 : offset
         *
         */
        if (bits_in_pointer != 64)
                return;

        add_hook(&global_variable, BASE_HOOK);
}