lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  PHC 
Open Source and information security mailing list archives
Hash Suite for Android: free password hash cracker in your pocket
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:   Tue, 8 Jan 2019 21:19:52 -0800
From:   Linus Torvalds <>
To:     "Michael S. Tsirkin" <>
Cc:     Dan Williams <>,
        Jason Wang <>,
        KVM list <>,,
        Netdev <>,
        Linux Kernel Mailing List <>,
        David Miller <>
Subject: Re: __get_user slower than get_user (was Re: [RFC PATCH V3 0/5] Hi:)

On Tue, Jan 8, 2019 at 8:31 PM Michael S. Tsirkin <> wrote:
> Linus, given that you just changed all users of access_ok anyway, do
> you still think that the access_ok() conversion to return a speculation
> sanitized pointer or NULL is too big a conversion?

I didn't actually change a single access_ok().

I changed the (very few) users of "user_access_begin()" to do an
access_ok() in them. There were 8 of them total.

It turns out that two of those cases (the strn*_user() ones) found
bugs in the implementation of access_ok() of two architectures, and
then looking at the others found that six more architectures also had
problems, but those weren't actually because of any access_ok()
changes, they were pre-existing issues. So we definitely had
unfortunate bugs in access_ok(), but they were mostly the benign kind
(ir the "use arguments twice - a real potential bug, but not one that
actually likely makes any difference to existing users)

Changing all 600+ users of access_ok() would be painful.

That said, one thing I *would* like to do is to just get rid of
__get_user() and __put_user() entirely. Or rather, just make them do
exactly the same thing that the normal "get_user()"/"put_user()"
functions do.

And then, _within_ the case of get_user()/put_user(), doing the
access_ok() as a data dependency rather than a lfence should be easy


Powered by blists - more mailing lists