linux-kernel - Re: [RFC PATCH 3/3] Prevent user from writing to IBT bitmap.

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Message-ID: <c99aa450d6cc9a0d23d24734a165e5ffbd9ecc7a.camel@intel.com>
Date:   Mon, 01 Jul 2019 12:48:56 -0700
From:   Yu-cheng Yu <yu-cheng.yu@...el.com>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     X86 ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Balbir Singh <bsingharora@...il.com>,
        Borislav Petkov <bp@...en8.de>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Dave Martin <Dave.Martin@....com>
Subject: Re: [RFC PATCH 3/3] Prevent user from writing to IBT bitmap.

On Sat, 2019-06-29 at 16:44 -0700, Andy Lutomirski wrote:
> On Fri, Jun 28, 2019 at 12:50 PM Yu-cheng Yu <yu-cheng.yu@...el.com> wrote:
> > 
> > The IBT bitmap is visiable from user-mode, but not writable.
> > 
> > Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
> > 
> > ---
> >  arch/x86/mm/fault.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> > index 59f4f66e4f2e..231196abb62e 100644
> > --- a/arch/x86/mm/fault.c
> > +++ b/arch/x86/mm/fault.c
> > @@ -1454,6 +1454,13 @@ void do_user_addr_fault(struct pt_regs *regs,
> >          * we can handle it..
> >          */
> >  good_area:
> > +#define USER_MODE_WRITE (FAULT_FLAG_WRITE | FAULT_FLAG_USER)
> > +       if (((flags & USER_MODE_WRITE)  == USER_MODE_WRITE) &&
> > +           (vma->vm_flags & VM_IBT)) {
> > +               bad_area_access_error(regs, hw_error_code, address, vma);
> > +               return;
> > +       }
> > +
> 
> Just make the VMA have VM_WRITE and VM_MAYWRITE clear.  No new code
> like this should be required.

Ok, I will work on that.

Thanks,
Yu-cheng