Messages in this thread | | | Date | Thu, 12 Jan 2012 17:22:31 +0100 | From | Oleg Nesterov <> | Subject | Re: [RFC,PATCH 1/2] seccomp_filters: system call filtering using BPF |
| |
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.
| |