linux-kernel - Re: [PATCH 1/2] x86: math-emu: check __copy_from

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Date:   Wed, 2 Oct 2019 09:11:23 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Kees Cook <keescook@...omium.org>
Cc:     Bill Metzenthen <billm@...bpc.org.au>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] x86: math-emu: check __copy_from_user result

On Wed, Oct 2, 2019 at 1:39 AM Kees Cook <keescook@...omium.org> wrote:

> > diff --git a/arch/x86/math-emu/reg_ld_str.c b/arch/x86/math-emu/reg_ld_str.c
> > index f3779743d15e..fe6246ff9887 100644
> > --- a/arch/x86/math-emu/reg_ld_str.c
> > +++ b/arch/x86/math-emu/reg_ld_str.c
> > @@ -85,7 +85,7 @@ int FPU_load_extended(long double __user *s, int stnr)
> >
> >       RE_ENTRANT_CHECK_OFF;
> >       FPU_access_ok(s, 10);
> > -     __copy_from_user(sti_ptr, s, 10);
> > +     FPU_copy_from_user(sti_ptr, s, 10);
>
> These access_ok() checks seem redundant everywhere in this file (after
> your switch from __copy* to copy*. I mean, I guess, just leave them, but
> *shrug*

There have always been duplicate/inconsistent for the get_user/put_user
case. I considered cleaning it all up but then decided to touch it as little
as possible.

       Arnd