linux-kernel - Re: [PATCH v7 03/14] x86/cet/ibt: Add IBT legacy code bitmap setup function

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Message-ID: <997ef050c13e3654dee6a862d810cffcafce249b.camel@intel.com>
Date:   Fri, 07 Jun 2019 12:23:46 -0700
From:   Yu-cheng Yu <yu-cheng.yu@...el.com>
To:     Dave Hansen <dave.hansen@...el.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...capital.net>,
        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: [PATCH v7 03/14] x86/cet/ibt: Add IBT legacy code bitmap setup
 function

On Fri, 2019-06-07 at 12:03 -0700, Dave Hansen wrote:
> On 6/6/19 1:09 PM, Yu-cheng Yu wrote:
> > +	modify_fpu_regs_begin();
> > +	rdmsrl(MSR_IA32_U_CET, r);
> > +	r |= (MSR_IA32_CET_LEG_IW_EN | bitmap);
> > +	wrmsrl(MSR_IA32_U_CET, r);
> > +	modify_fpu_regs_end();
> 
> Isn't there a bunch of other stuff in this MSR?  It seems like the
> bitmap value would allow overwriting lots of bits in the MSR that have
> nothing to do with the bitmap... in a prctl() that's supposed to only be
> dealing with the bitmap.

Yes, the bitmap address should have been masked, although it is checked for page
alignment (which has the same effect).  I will fix it.

Yu-cheng