so we can use speculation barrier? and fix the problem locally


On 8/22/2025 5:52 PM, Linus Torvalds wrote:

On Fri, 22 Aug 2025 at 05:58, Christophe Leroy
[off-list ref] wrote:

quoted

quoted

The results of "access_ok()" can be mis-speculated. The result is 

that > you can end speculatively: > > if (access_ok(from, size)) > // 
Right here
I actually think that we should probably just make access_ok() itself do this.

We don't have *that* many users since we have been de-emphasizing the
"check ahead of time" model, and any that are performance-critical can
these days be turned into masked addresses.

As it is, now we're in the situation that careful places - like
_inline_copy_from_user(), and with your patch  copy_from_user_iter() -
do maybe wethis by hand and are ugly as a result, and lazy and
probably incorrect places don't do it at all.

That said, I don't object to this patch and maybe we should do that
access_ok() change later and independently of any powerpc work.

                  Linus