linux-kernel - Re: [PATCH v9 23/42] Documentation/x86: Add CET shadow stack description

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <0a9ade13b989ea881fd43fabbe5de1d248cf4218.camel@intel.com>
Date:   Wed, 5 Jul 2023 19:17:25 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "broonie@...nel.org" <broonie@...nel.org>
CC:     "Xu, Pengfei" <pengfei.xu@...el.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "kcc@...gle.com" <kcc@...gle.com>,
        "Lutomirski, Andy" <luto@...nel.org>,
        "nadav.amit@...il.com" <nadav.amit@...il.com>,
        "szabolcs.nagy@....com" <szabolcs.nagy@....com>,
        "david@...hat.com" <david@...hat.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "Schimpe, Christina" <christina.schimpe@...el.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "corbet@....net" <corbet@....net>, "nd@....com" <nd@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dethoma@...rosoft.com" <dethoma@...rosoft.com>,
        "jannh@...gle.com" <jannh@...gle.com>,
        "debug@...osinc.com" <debug@...osinc.com>,
        "mike.kravetz@...cle.com" <mike.kravetz@...cle.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "rdunlap@...radead.org" <rdunlap@...radead.org>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "john.allen@....com" <john.allen@....com>,
        "jamorris@...ux.microsoft.com" <jamorris@...ux.microsoft.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "rppt@...nel.org" <rppt@...nel.org>,
        "bsingharora@...il.com" <bsingharora@...il.com>,
        "x86@...nel.org" <x86@...nel.org>, "pavel@....cz" <pavel@....cz>,
        "andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>,
        "oleg@...hat.com" <oleg@...hat.com>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "gorcunov@...il.com" <gorcunov@...il.com>,
        "fweimer@...hat.com" <fweimer@...hat.com>,
        "Yu, Yu-cheng" <yu-cheng.yu@...el.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hjl.tools@...il.com" <hjl.tools@...il.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Syromiatnikov, Eugene" <esyr@...hat.com>,
        "Torvalds, Linus" <torvalds@...ux-foundation.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "Yang, Weijiang" <weijiang.yang@...el.com>,
        "Eranian, Stephane" <eranian@...gle.com>
Subject: Re: [PATCH v9 23/42] Documentation/x86: Add CET shadow stack
 description

On Wed, 2023-07-05 at 20:10 +0100, Mark Brown wrote:
> On Wed, Jul 05, 2023 at 06:45:38PM +0000, Edgecombe, Rick P wrote:
> 
> > Looking at the docs Mark linked (thanks!), ARM has generic GCS PUSH
> > and
> > POP shadow stack instructions? Can ARM just push a restore token at
> > setjmp time, like I was trying to figure out earlier with a push
> > token
> > arch_prctl? It would be good to understand how ARM is going to
> > implement this with these differences in what is allowed by the HW.
> 
> > If there are differences in how locked down/functional the hardware
> > implementations are, and if we want to have some unified set of
> > rules
> > for apps, there will need to some give and take. The x86 approach
> > was
> > mostly to not support all behaviors and ask apps to either change
> > or
> > not enable shadow stacks. We don't want one architecture to have to
> > do
> > a bunch of strange things, but we also don't want one to lose some
> > key
> > end user value.
> 
> GCS is all or nothing, either the hardware supports GCS or it
> doesn't.
> There are finer grained hypervisor traps (see HFGxTR_EL2 in the
> system
> registers) but they aren't intended to be used to disable partial
> functionality and there's a strong chance we'd just disable the
> feature
> in the face of such usage.  The kernel does have the option to
> control
> which functionality is exposed to userspace, in particular we have
> separate controls for use of the GCS, the push/pop instructions and
> the
> store instructions (similarly to the control x86 has for WRSS).
> Similarly to the handling of WRSS in your series my patches allow
> userspace to choose which of these features are enabled.

Ah, interesting, thanks for the extra info. So which features is glibc
planning to use? (probably more of a question for Szabolcs). Are push
and pop controllable separately?