Messages in this thread | | | Date | Mon, 7 Oct 2019 18:34:32 +0100 | From | Al Viro <> | Subject | Re: [PATCH] Convert filldir[64]() from __put_user() to unsafe_put_user() |
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On Sun, Oct 06, 2019 at 08:11:42PM -0700, Linus Torvalds wrote:
> > So do we want to bother with separation between raw_copy_to_user() and > > unsafe_copy_to_user()? After all, __copy_to_user() also has only few > > callers, most of them in arch/* > > No, you're right. Just switch over. > > > I'll take a look into that tomorrow - half-asleep right now... > > Thanks. No huge hurry.
Tangentially related: copy_regster_to_user() and copy_regset_from_user(). That's where we do access_ok(), followed by calls of ->get() and ->set() resp. Those tend to either use user_regset_copy{out,in}(), or open-code those. The former variant tends to lead to few calls of __copy_{to,from}_user(); the latter... On x86 it ends up doing this: static int genregs_get(struct task_struct *target, const struct user_regset *regset, unsigned int pos, unsigned int count, void *kbuf, void __user *ubuf) { if (kbuf) { unsigned long *k = kbuf; while (count >= sizeof(*k)) { *k++ = getreg(target, pos); count -= sizeof(*k); pos += sizeof(*k); } } else { unsigned long __user *u = ubuf; while (count >= sizeof(*u)) { if (__put_user(getreg(target, pos), u++)) return -EFAULT; count -= sizeof(*u); pos += sizeof(*u); } }
return 0; }
Potentially doing arseloads of stac/clac as it goes. OTOH, getreg() (and setreg()) in there are not entirely trivial, so blanket user_access_begin()/user_access_end() over the entire loop might be a bad idea...
How hot is that codepath? I know that arch/um used to rely on it (== PTRACE_[GS]ETREGS) quite a bit...
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