linux-kernel - Re: [tip:x86/mpx] x86/insn-eval: Add utility function to get segment descriptor

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Message-ID: <20171207080312.6izk3edr2ctng6sd@pd.tnic>
Date:   Thu, 7 Dec 2017 09:03:12 +0100
From:   Borislav Petkov <bp@...e.de>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>, luto@...nel.org,
        adam.buchbinder@...il.com, mst@...hat.com, mhiramat@...nel.org,
        dave.hansen@...ux.intel.com, mingo@...nel.org,
        linux-kernel@...r.kernel.org, colin.king@...onical.com,
        jslaby@...e.cz, pbonzini@...hat.com, cmetcalf@...lanox.com,
        akpm@...ux-foundation.org, vbabka@...e.cz, acme@...hat.com,
        brgerst@...il.com, shuah@...nel.org, paul.gortmaker@...driver.com,
        lstoakes@...il.com, hpa@...or.com, thgarnie@...gle.com,
        keescook@...omium.org, adrian.hunter@...el.com, ray.huang@....com,
        dvyukov@...gle.com, ravi.v.shankar@...el.com, slaoub@...il.com,
        corbet@....net, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/mpx] x86/insn-eval: Add utility function to get segment
 descriptor

On Wed, Dec 06, 2017 at 11:23:59PM -0800, Ricardo Neri wrote:
> In UMIP emulation we can potentially access the LDT twice. Once when
> determining the base address of the code segment and again when determining
> the base address and limit of the segment in which the result of the
> emulation is written. I guess that mm->context.ldt_seq needs to not change
> not only while decoding a particular linear address but across these two
> linear address decodings.

Yap, stuff which needs to see an *unchanged* LDT should use the cookie
to verify that and the LDT code should change the cookie when the LDT
is modified.

> Sure, I will look into implementing this idea and post patches for it.

Thanks!

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--