linux-kernel - Re: [RFC PATCH v0 3/6] x86: Enable Upper Address Ignore(UAI) feature

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Date:   Thu, 10 Mar 2022 14:46:20 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     David Laight <David.Laight@...LAB.COM>,
        'Andrew Cooper' <Andrew.Cooper3@...rix.com>,
        Bharata B Rao <bharata@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "will@...nel.org" <will@...nel.org>,
        "shuah@...nel.org" <shuah@...nel.org>,
        "oleg@...hat.com" <oleg@...hat.com>,
        "ananth.narayan@....com" <ananth.narayan@....com>
Subject: Re: [RFC PATCH v0 3/6] x86: Enable Upper Address Ignore(UAI) feature

On 3/10/22 14:37, David Laight wrote:
> Just letting user address space be aliased a lot of times doesn't
> seem like a security feature to me.
> It must have some strange use case.

This should have been in the changelogs... sheesh...

Right now, address sanitizers keep pointer metadata in various spots.
But, it requires recompiling apps and libraries.  These compiler-based
things are also so slow that production use is rare.

These masking things (ARM TBI, AMD UAI, Intel LAM) _theoretically_ let
you plumb enough metadata around with pointers to do address sanitizer
implementations in production.

I think LAM is the most sane of the three, but I'm biased.