On 01/11, Will Drewry wrote:
>
> +__weak u8 *seccomp_get_regs(u8 *scratch, size_t *available)
> +{
> + /* regset is usually returned based on task personality, not current
> + * system call convention. This behavior makes it unsafe to execute
> + * BPF programs over regviews if is_compat_task or the personality
> + * have changed since the program was installed.
> + */
> + const struct user_regset_view *view = task_user_regset_view(current);
> + const struct user_regset *regset = &view->regsets[0];
> + size_t scratch_size = *available;
> + if (regset->core_note_type != NT_PRSTATUS) {
> + /* The architecture should override this method for speed. */
> + regset = find_prstatus(view);
> + if (!regset)
> + return NULL;
> + }
> + *available = regset->n * regset->size;
> + /* Make sure the scratch space isn't exceeded. */
> + if (*available > scratch_size)
> + *available = scratch_size;
> + if (regset->get(current, regset, 0, *available, scratch, NULL))
> + return NULL;
> + return scratch;
> +}
> +
> +/**
> + * seccomp_test_filters - tests 'current' against the given syscall
> + * @syscall: number of the system call to test
> + *
> + * Returns 0 on ok and non-zero on error/failure.
> + */
> +int seccomp_test_filters(int syscall)
> +{
> + struct seccomp_filter *filter;
> + u8 regs_tmp[sizeof(struct user_regs_struct)], *regs;
> + size_t regs_size = sizeof(struct user_regs_struct);
> + int ret = -EACCES;
> +
> + filter = current->seccomp.filter; /* uses task ref */
> + if (!filter)
> + goto out;
> +
> + /* All filters in the list are required to share the same system call
> + * convention so only the first filter is ever checked.
> + */
> + if (seccomp_check_personality(filter))
> + goto out;
> +
> + /* Grab the user_regs_struct. Normally, regs == ®s_tmp, but
> + * that is not mandatory. E.g., it may return a point to
> + * task_pt_regs(current). NULL checking is mandatory.
> + */
> + regs = seccomp_get_regs(regs_tmp, ®s_size);
Stupid question. I am sure you know what are you doing ;) and I know
nothing about !x86 arches.
But could you explain why it is designed to use user_regs_struct ?
Why we can't simply use task_pt_regs() and avoid the (costly) regsets?
Just curious.
Oleg.
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