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    Subject[PATCH v4 09/10] kallsyms: Hide layout
    Date
    This patch makes /proc/kallsyms display in a random order, rather
    than sorted by address in order to hide the newly randomized address
    layout.

    Signed-off-by: Kristen Carlson Accardi <kristen@linux.intel.com>
    Reviewed-by: Tony Luck <tony.luck@intel.com>
    Tested-by: Tony Luck <tony.luck@intel.com>
    ---
    kernel/kallsyms.c | 163 +++++++++++++++++++++++++++++++++++++++++++++-
    1 file changed, 162 insertions(+), 1 deletion(-)

    diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
    index bb14e64f62a4..45d147f7f10e 100644
    --- a/kernel/kallsyms.c
    +++ b/kernel/kallsyms.c
    @@ -446,6 +446,12 @@ struct kallsym_iter {
    int show_value;
    };

    +struct kallsyms_shuffled_iter {
    + struct kallsym_iter iter;
    + loff_t total_syms;
    + loff_t shuffled_index[];
    +};
    +
    int __weak arch_get_kallsym(unsigned int symnum, unsigned long *value,
    char *type, char *name)
    {
    @@ -661,7 +667,7 @@ bool kallsyms_show_value(const struct cred *cred)
    }
    }

    -static int kallsyms_open(struct inode *inode, struct file *file)
    +static int __kallsyms_open(struct inode *inode, struct file *file)
    {
    /*
    * We keep iterator in m->private, since normal case is to
    @@ -682,6 +688,161 @@ static int kallsyms_open(struct inode *inode, struct file *file)
    return 0;
    }

    +/*
    + * When function granular kaslr is enabled, we need to print out the symbols
    + * at random so we don't reveal the new layout.
    + */
    +#if defined(CONFIG_FG_KASLR)
    +static int update_random_pos(struct kallsyms_shuffled_iter *s_iter,
    + loff_t pos, loff_t *new_pos)
    +{
    + loff_t new;
    +
    + if (pos >= s_iter->total_syms)
    + return 0;
    +
    + new = s_iter->shuffled_index[pos];
    +
    + /*
    + * normally this would be done as part of update_iter, however,
    + * we want to avoid triggering this in the event that new is
    + * zero since we don't want to blow away our pos end indicators.
    + */
    + if (new == 0) {
    + s_iter->iter.name[0] = '\0';
    + s_iter->iter.nameoff = get_symbol_offset(new);
    + s_iter->iter.pos = new;
    + }
    +
    + *new_pos = new;
    + return 1;
    +}
    +
    +static void *shuffled_start(struct seq_file *m, loff_t *pos)
    +{
    + struct kallsyms_shuffled_iter *s_iter = m->private;
    + loff_t new_pos;
    +
    + if (!update_random_pos(s_iter, *pos, &new_pos))
    + return NULL;
    +
    + return s_start(m, &new_pos);
    +}
    +
    +static void *shuffled_next(struct seq_file *m, void *p, loff_t *pos)
    +{
    + struct kallsyms_shuffled_iter *s_iter = m->private;
    + loff_t new_pos;
    +
    + (*pos)++;
    +
    + if (!update_random_pos(s_iter, *pos, &new_pos))
    + return NULL;
    +
    + if (!update_iter(m->private, new_pos))
    + return NULL;
    +
    + return p;
    +}
    +
    +/*
    + * shuffle_index_list()
    + * Use a Fisher Yates algorithm to shuffle a list of text sections.
    + */
    +static void shuffle_index_list(loff_t *indexes, loff_t size)
    +{
    + int i;
    + unsigned int j;
    + loff_t temp;
    +
    + for (i = size - 1; i > 0; i--) {
    + /* pick a random index from 0 to i */
    + get_random_bytes(&j, sizeof(j));
    + j = j % (i + 1);
    +
    + temp = indexes[i];
    + indexes[i] = indexes[j];
    + indexes[j] = temp;
    + }
    +}
    +
    +static const struct seq_operations kallsyms_shuffled_op = {
    + .start = shuffled_start,
    + .next = shuffled_next,
    + .stop = s_stop,
    + .show = s_show
    +};
    +
    +static int kallsyms_random_open(struct inode *inode, struct file *file)
    +{
    + loff_t pos;
    + struct kallsyms_shuffled_iter *shuffled_iter;
    + struct kallsym_iter iter;
    + bool show_value;
    +
    + /*
    + * If privileged, go ahead and use the normal algorithm for
    + * displaying symbols
    + */
    + show_value = kallsyms_show_value(file->f_cred);
    + if (show_value)
    + return __kallsyms_open(inode, file);
    +
    + /*
    + * we need to figure out how many extra symbols there are
    + * to print out past kallsyms_num_syms
    + */
    + pos = kallsyms_num_syms;
    + reset_iter(&iter, 0);
    + do {
    + if (!update_iter(&iter, pos))
    + break;
    + pos++;
    + } while (1);
    +
    + /*
    + * add storage space for an array of loff_t equal to the size
    + * of the total number of symbols we need to print
    + */
    + shuffled_iter = __seq_open_private(file, &kallsyms_shuffled_op,
    + sizeof(*shuffled_iter) +
    + (sizeof(pos) * pos));
    + if (!shuffled_iter)
    + return -ENOMEM;
    +
    + reset_iter(&shuffled_iter->iter, 0);
    + shuffled_iter->iter.show_value = show_value;
    + shuffled_iter->total_syms = pos;
    +
    + /*
    + * the existing update_iter algorithm requires that we
    + * are either moving along increasing pos sequentially,
    + * or that these values are correct. Since these values
    + * were discovered above, initialize our new iter so we
    + * can use update_iter non-sequentially.
    + */
    + shuffled_iter->iter.pos_arch_end = iter.pos_arch_end;
    + shuffled_iter->iter.pos_mod_end = iter.pos_mod_end;
    + shuffled_iter->iter.pos_ftrace_mod_end = iter.pos_ftrace_mod_end;
    +
    + /*
    + * initialize the array with all possible pos values, then
    + * shuffle the array so that the values will display in a random
    + * order.
    + */
    + for (pos = 0; pos < shuffled_iter->total_syms; pos++)
    + shuffled_iter->shuffled_index[pos] = pos;
    +
    + shuffle_index_list(shuffled_iter->shuffled_index, shuffled_iter->total_syms);
    +
    + return 0;
    +}
    +
    +#define kallsyms_open kallsyms_random_open
    +#else
    +#define kallsyms_open __kallsyms_open
    +#endif /* CONFIG_FG_KASLR */
    +
    #ifdef CONFIG_KGDB_KDB
    const char *kdb_walk_kallsyms(loff_t *pos)
    {
    --
    2.20.1
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