Re: [PATCH v2 02/10] uaccess: Add speculation barrier to copy_from_user_iter()

[Giorgi Tchankvetadze <giorgitchankvetadze1997@gmail.com>]

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
> <christophe.leroy@csgroup.eu> wrote:
>> > 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
>