Hey again, On Thu, Nov 24, 2022 at 01:24:42PM +0100, Jason A. Donenfeld wrote: > Hi Florian, > > On Thu, Nov 24, 2022 at 01:15:24PM +0100, Florian Weimer wrote: > > * Jason A. Donenfeld: > > > > > Hi Florian, > > > > > > On Thu, Nov 24, 2022 at 06:25:39AM +0100, Florian Weimer wrote: > > >> * Jason A. Donenfeld: > > >> > > >> > Hi Florian, > > >> > > > >> > On Wed, Nov 23, 2022 at 11:46:58AM +0100, Florian Weimer wrote: > > >> >> * Jason A. Donenfeld: > > >> >> > > >> >> > + * The vgetrandom() function in userspace requires an opaque state, which this > > >> >> > + * function provides to userspace, by mapping a certain number of special pages > > >> >> > + * into the calling process. It takes a hint as to the number of opaque states > > >> >> > + * desired, and returns the number of opaque states actually allocated, the > > >> >> > + * size of each one in bytes, and the address of the first state. > > >> >> > + */ > > >> >> > +SYSCALL_DEFINE3(vgetrandom_alloc, unsigned long __user *, num, > > >> >> > + unsigned long __user *, size_per_each, unsigned int, flags) > > >> >> > > >> >> I think you should make this __u64, so that you get a consistent > > >> >> userspace interface on all architectures, without the need for compat > > >> >> system calls. > > >> > > > >> > That would be quite unconventional. Most syscalls that take lengths do > > >> > so with the native register size (`unsigned long`, `size_t`), rather > > >> > than u64. If you can point to a recent trend away from this by > > >> > indicating some commits that added new syscalls with u64, I'd be happy > > >> > to be shown otherwise. But AFAIK, that's not the way it's done. > > >> > > >> See clone3 and struct clone_args. > > > > > > The struct is one thing. But actually, clone3 takes a `size_t`: > > > > > > SYSCALL_DEFINE2(clone3, struct clone_args __user *, uargs, size_t, size) > > > > > > I take from this that I too should use `size_t` rather than `unsigned > > > long.` And it doesn't seem like there's any compat clone3. > > > > But vgetrandom_alloc does not use unsigned long, but unsigned long *. > > You need to look at the contents for struct clone_args for comparison. > > Ah! I see what you mean; that's a good point. The usual register > clearing thing isn't going to happen because these are addresses. > > I still am somewhat hesitant, though, because `size_t` is really the > "proper" type to be used. Maybe the compat syscall thing is just a > necessary evil? > > The other direction would be making this a u32, since 640k ought to be > enough for anybody and such, but maybe that'd be a mistake too. > > So I'm not sure. Anybody else on the list with experience adding > syscalls have an opinion? Looks like set_mempolicy, get_mempoliy, and migrate_pages pass an unsigned long pointer and I don't see any compat stuff around it: SYSCALL_DEFINE3(set_mempolicy, int, mode, const unsigned long __user *, nmask, unsigned long, maxnode) SYSCALL_DEFINE5(get_mempolicy, int __user *, policy, unsigned long __user *, nmask, unsigned long, maxnode, unsigned long, addr, unsigned long, flags) SYSCALL_DEFINE4(migrate_pages, pid_t, pid, unsigned long, maxnode, const unsigned long __user *, old_nodes, const unsigned long __user *, new_nodes) In contrast sched_setaffinity and get_robust_list take a unsigned long pointer and does have a compat wrapper: SYSCALL_DEFINE3(sched_setaffinity, pid_t, pid, unsigned int, len, unsigned long __user *, user_mask_ptr) SYSCALL_DEFINE3(get_robust_list, int, pid, struct robust_list_head __user * __user *, head_ptr, size_t __user *, len_ptr) Jason