linux-kernel - Re: [PATCH 8/9] x86: kvm_hv_set_msr(): use __put_user() instead of 32bit __clear

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Message-ID: <20200530191940.GS23230@ZenIV.linux.org.uk>
Date:   Sat, 30 May 2020 20:19:40 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        KVM list <kvm@...r.kernel.org>
Subject: Re: [PATCH 8/9] x86: kvm_hv_set_msr(): use __put_user() instead of
 32bit __clear_user()

On Sat, May 30, 2020 at 11:52:44AM -0700, Linus Torvalds wrote:

> And I don't understand why you mention set_fs() vs access_ok(). None
> of this code has anything that messes with set_fs(). The access_ok()
> is garbage and shouldn't exist, and those user accesses should all use
> the checking versions and the double underscores are wrong.
> 
> I have no idea why you think the double underscores could _possibly_
> be worth defending.

I do not.  What I'm saying is that this just might be a beast different
from *both* __... and the normal ones.  I'm not saying that this
__put_user() (or __clear_user(), etc.) is the right primitive here.
If anything, it's closer to the situation for (x86) copy_stack_trace().