| 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
| ||
|
Message-ID: <8d709a88251df3695579c851f9ee28032f9e7c1e.camel@intel.com>
Date: Thu, 20 Oct 2022 21:22:17 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "nathan@...nel.org" <nathan@...nel.org>
CC: "bsingharora@...il.com" <bsingharora@...il.com>,
"hpa@...or.com" <hpa@...or.com>,
"Syromiatnikov, Eugene" <esyr@...hat.com>,
"babu.moger@....com" <babu.moger@....com>,
"peterz@...radead.org" <peterz@...radead.org>,
"rdunlap@...radead.org" <rdunlap@...radead.org>,
"keescook@...omium.org" <keescook@...omium.org>,
"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
"kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
"Eranian, Stephane" <eranian@...gle.com>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"fweimer@...hat.com" <fweimer@...hat.com>,
"nadav.amit@...il.com" <nadav.amit@...il.com>,
"jannh@...gle.com" <jannh@...gle.com>,
"dethoma@...rosoft.com" <dethoma@...rosoft.com>,
"kcc@...gle.com" <kcc@...gle.com>,
"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
"bp@...en8.de" <bp@...en8.de>, "oleg@...hat.com" <oleg@...hat.com>,
"hjl.tools@...il.com" <hjl.tools@...il.com>,
"pavel@....cz" <pavel@....cz>,
"Lutomirski, Andy" <luto@...nel.org>,
"thomas.lendacky@....com" <thomas.lendacky@....com>,
"jamorris@...ux.microsoft.com" <jamorris@...ux.microsoft.com>,
"arnd@...db.de" <arnd@...db.de>,
"Moreira, Joao" <joao.moreira@...el.com>,
"tglx@...utronix.de" <tglx@...utronix.de>,
"x86@...nel.org" <x86@...nel.org>,
"mike.kravetz@...cle.com" <mike.kravetz@...cle.com>,
"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
"gustavoars@...nel.org" <gustavoars@...nel.org>,
"john.allen@....com" <john.allen@....com>,
"rppt@...nel.org" <rppt@...nel.org>,
"Shankar, Ravi V" <ravi.v.shankar@...el.com>,
"ndesaulniers@...gle.com" <ndesaulniers@...gle.com>,
"Hansen, Dave" <dave.hansen@...el.com>,
"mingo@...hat.com" <mingo@...hat.com>,
"corbet@....net" <corbet@....net>,
"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"Yang, Weijiang" <weijiang.yang@...el.com>,
"gorcunov@...il.com" <gorcunov@...il.com>
Subject: Re: [PATCH v2 33/39] x86/cpufeatures: Limit shadow stack to Intel
CPUs
On Tue, 2022-10-04 at 13:50 -0700, Nathan Chancellor wrote:
> On Tue, Oct 04, 2022 at 08:34:54PM +0000, Edgecombe, Rick P wrote:
> > On Tue, 2022-10-04 at 14:43 -0500, John Allen wrote:
> > > On 10/4/22 10:47 AM, Nathan Chancellor wrote:
> > > > Hi Kees,
> > > >
> > > > On Mon, Oct 03, 2022 at 09:54:26PM -0700, Kees Cook wrote:
> > > > > On Mon, Oct 03, 2022 at 05:09:04PM -0700, Dave Hansen wrote:
> > > > > > On 10/3/22 16:57, Kees Cook wrote:
> > > > > > > On Thu, Sep 29, 2022 at 03:29:30PM -0700, Rick Edgecombe
> > > > > > > wrote:
> > > > > > > > Shadow stack is supported on newer AMD processors, but
> > > > > > > > the
> > > > > > > > kernel
> > > > > > > > implementation has not been tested on them. Prevent
> > > > > > > > basic
> > > > > > > > issues from
> > > > > > > > showing up for normal users by disabling shadow stack
> > > > > > > > on
> > > > > > > > all CPUs except
> > > > > > > > Intel until it has been tested. At which point the
> > > > > > > > limitation should be
> > > > > > > > removed.
> > > > > > > >
> > > > > > > > Signed-off-by: Rick Edgecombe <
> > > > > > > > rick.p.edgecombe@...el.com>
> > > > > > >
> > > > > > > So running the selftests on an AMD system is sufficient
> > > > > > > to
> > > > > > > drop this
> > > > > > > patch?
> > > > > >
> > > > > > Yes, that's enough.
> > > > > >
> > > > > > I _thought_ the AMD folks provided some tested-by's at some
> > > > > > point in the
> > > > > > past. But, maybe I'm confusing this for one of the other
> > > > > > shared
> > > > > > features. Either way, I'm sure no tested-by's were dropped
> > > > > > on
> > > > > > purpose.
> > > > > >
> > > > > > I'm sure Rick is eager to trim down his series and this
> > > > > > would
> > > > > > be a great
> > > > > > patch to drop. Does anyone want to make that easy for
> > > > > > Rick?
> > > > > >
> > > > > > <hint> <hint>
> > > > >
> > > > > Hey Gustavo, Nathan, or Nick! I know y'all have some fancy
> > > > > AMD
> > > > > testing
> > > > > rigs. Got a moment to spin up this series and run the
> > > > > selftests?
> > > > > :)
> > > >
> > > > I do have access to a system with an EPYC 7513, which does have
> > > > Shadow
> > > > Stack support (I can see 'shstk' in the "Flags" section of
> > > > lscpu
> > > > with
> > > > this series). As far as I understand it, AMD only added Shadow
> > > > Stack
> > > > with Zen 3; my regular AMD test system is Zen 2 (probably
> > > > should
> > > > look at
> > > > procurring a Zen 3 or Zen 4 one at some point).
> > > >
> > > > I applied this series on top of 6.0 and reverted this change
> > > > then
> > > > booted
> > > > it on that system. After building the selftest (which did
> > > > require
> > > > 'make headers_install' and a small addition to make it build
> > > > beyond
> > > > that, see below), I ran it and this was the result. I am not
> > > > sure
> > > > if
> > > > that is expected or not but the other results seem promising
> > > > for
> > > > dropping this patch.
> > > >
> > > > $ ./test_shadow_stack_64
> > > > [INFO] new_ssp = 7f8a36c9fff8, *new_ssp = 7f8a36ca0001
> > > > [INFO] changing ssp from 7f8a374a0ff0 to 7f8a36c9fff8
> > > > [INFO] ssp is now 7f8a36ca0000
> > > > [OK] Shadow stack pivot
> > > > [OK] Shadow stack faults
> > > > [INFO] Corrupting shadow stack
> > > > [INFO] Generated shadow stack violation successfully
> > > > [OK] Shadow stack violation test
> > > > [INFO] Gup read -> shstk access success
> > > > [INFO] Gup write -> shstk access success
> > > > [INFO] Violation from normal write
> > > > [INFO] Gup read -> write access success
> > > > [INFO] Violation from normal write
> > > > [INFO] Gup write -> write access success
> > > > [INFO] Cow gup write -> write access success
> > > > [OK] Shadow gup test
> > > > [INFO] Violation from shstk access
> > > > [OK] mprotect() test
> > > > [OK] Userfaultfd test
> > > > [FAIL] Alt shadow stack test
> > >
> > > The selftest is looking OK on my system (Dell PowerEdge R6515 w/
> > > EPYC
> > > 7713). I also just pulled a fresh 6.0 kernel and applied the
> > > series
> > > including the fix Nathan mentions below.
> > >
> > > $ tools/testing/selftests/x86/test_shadow_stack_64
> > > [INFO] new_ssp = 7f30cccc5ff8, *new_ssp = 7f30cccc6001
> > > [INFO] changing ssp from 7f30cd4c6ff0 to 7f30cccc5ff8
> > > [INFO] ssp is now 7f30cccc6000
> > > [OK] Shadow stack pivot
> > > [OK] Shadow stack faults
> > > [INFO] Corrupting shadow stack
> > > [INFO] Generated shadow stack violation successfully
> > > [OK] Shadow stack violation test
> > > [INFO] Gup read -> shstk access success
> > > [INFO] Gup write -> shstk access success
> > > [INFO] Violation from normal write
> > > [INFO] Gup read -> write access success
> > > [INFO] Violation from normal write
> > > [INFO] Gup write -> write access success
> > > [INFO] Cow gup write -> write access success
> > > [OK] Shadow gup test
> > > [INFO] Violation from shstk access
> > > [OK] mprotect() test
> > > [OK] Userfaultfd test
> > > [OK] Alt shadow stack test.
> >
> > Thanks for the testing. Based on the test, I wonder if this could
> > be a
> > SW bug. Nathan, could I send you a tweaked test with some more
> > debug
> > information?
>
> Yes, more than happy to help you look into this further!
Indeed this was a SW bug and had nothing to do with the CPU model. The
altshstk selftest was not fully initializing the stack_t struct, and
getting lucky on some compilers. Thanks to Nathan for helping me debug
it.
Powered by blists - more mailing lists