From: "H.J. Lu" <hjl.tools@gmail.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>
Cc: "bp@alien8.de" <bp@alien8.de>,
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Subject: Re: [PATCH v7 28/41] x86: Introduce userspace API for shadow stack
Date: Thu, 9 Mar 2023 18:03:49 -0800 [thread overview]
Message-ID: <CAMe9rOrK2d6+Y_Xb+NUW4i+GWRbX+mGx+mJLwnEAB4hvsQ_eiw@mail.gmail.com> (raw)
In-Reply-To: <e83ee9fc1a6e98cab62b681de7209598394df911.camel@intel.com>
On Thu, Mar 9, 2023 at 5:13 PM Edgecombe, Rick P
<rick.p.edgecombe@intel.com> wrote:
>
> +Joao regarding mixed mode designs
>
> On Fri, 2023-03-10 at 00:51 +0100, Borislav Petkov wrote:
> > On Thu, Mar 09, 2023 at 04:56:37PM +0000, Edgecombe, Rick P wrote:
> > > There is a proc that shows if shadow stack is enabled in a thread.
> > > It
> > > does indeed come later in the series.
> >
> > Not good enough:
> >
> > 1. buried somewhere in proc where no one knows about it
> >
> > 2. it is per thread so user needs to grep *all*
>
> See "x86: Expose thread features in /proc/$PID/status" for the patch.
> We could emit something in dmesg I guess? The logic would be:
> - Record the presence of elf SHSTK bit on exec
> - On shadow stack disable, if it had the elf bit, pr_info("bad!")
>
> >
> > > ... We previously tried to add some batch operations to improve
> > > the
> > > performance, but tglx had suggested to start with something
> > > simple.
> > > So we end up with this simple composable API.
> >
> > I agree with starting simple and thanks for explaining this in
> > detail.
> >
> > TBH, though, it already sounds like a mess to me. I guess a mess
> > we'll
> > have to deal with because there will always be this case of some
> > shared object/lib not being enabled for shstk because of raisins.
>
> The compatibility problems are totally the mess in this whole thing.
> When you try to look at a "permissive" mode that actually works it gets
> even more complex. Joao and I have been banging our heads on that
> problem for months.
>
> But there are some expected users of this that say: we compile and
> check our known set of binaries, we won't get any surprises. So it's
> more of a distro problem.
>
> >
> > And TBH #2, I would've done it even simpler: if some shared object
> > can't
> > do shadow stack, we disable it for the whole process. I mean, what's
> > the
> > point?
>
> You mean a late loaded dlopen()ed DSO? The enabling logic can't know
> this will happen ahead of time.
>
> If you mean if the shared objects in the elf all support shadow stack,
> then this is what happens. The complication is that the loader wants to
> enable shadow stack before it has checked the elf libs so it doesn't
> underflow the shadow stack when it returns from the function that does
> this checking.
>
> So it does:
> 1. Enable shadow stack
> 2. Call elf libs checking functions
> 3. If all good, lock shadow stack. Else, disable shadow stack.
> 4. Return from elf checking functions and if shstk is enabled, don't
> underflow because it was enabled in step 1 and we have return addresses
> from 2 on the shadow stack
>
> I'm wondering if this can't be improved in glibc to look like:
> 1. Check elf libs, and record it somewhere
> 2. Wait until just the right spot
> 3. If all good, enable and lock shadow stack.
I will try it out.
> But it depends on the loader code design which I don't know well
> enough.
>
> > Only some of the stack is shadowed so an attacker could find
> > a way to keep the process perhaps run this shstk-unsupporting shared
> > object more/longer and ROP its way around the system.
>
> I hope non-permissive mode is the standard usage eventually.
>
> >
> > But I tend to oversimplify things sometimes so...
> >
> > What I'd like to have, though, is a kernel cmdline param which
> > disables
> > permissive mode and userspace can't do anything about it. So that
> > once
> > you boot your kernel, you can know that everything that runs on the
> > machine has shstk and is properly protected.
>
> Szabolcs Nagy was commenting something similar in another thread, for
> supporting kernel enforced security policies. I think the way to do it
> would have the kernel detect the the elf bit itself (like it used to)
> and enable shadow stack on exec. If you can't rely on userspace to call
> in to enable it, it's not clear at what point the kernel should check
> that it did.
>
> But then if you trigger off of the elf bit in the kernel, you get all
> the regression issues of the old glibcs at that point. But it is
> already an "I don't care if I crash" mode, so...
>
> I think if you trust your libc, glibc could implement this in userspace
> too. It would be useful even as as testing override.
>
> >
> > Also, it'll allow for faster fixing of all those shared objects to
> > use
> > shstk by way of political pressure.
--
H.J.
next prev parent reply other threads:[~2023-03-10 2:04 UTC|newest]
Thread overview: 154+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-27 22:29 [PATCH v7 00/41] Shadow stacks for userspace Rick Edgecombe
2023-02-27 22:29 ` [PATCH v7 01/41] Documentation/x86: Add CET shadow stack description Rick Edgecombe
2023-03-01 14:21 ` Szabolcs Nagy
2023-03-01 14:38 ` Szabolcs Nagy
2023-03-01 18:07 ` Edgecombe, Rick P
2023-03-01 18:32 ` Edgecombe, Rick P
[not found] ` <ZADQISkczejfgdoS@arm.com>
2023-03-03 22:35 ` Edgecombe, Rick P
[not found] ` <ZAYS6CHuZ0MiFvmE@arm.com>
2023-03-06 16:31 ` Florian Weimer
2023-03-06 18:08 ` Edgecombe, Rick P
2023-03-07 13:03 ` szabolcs.nagy
2023-03-07 14:00 ` Florian Weimer
2023-03-06 18:05 ` Edgecombe, Rick P
2023-03-06 20:31 ` Liang, Kan
2023-03-02 16:14 ` szabolcs.nagy
2023-03-02 21:17 ` Edgecombe, Rick P
2023-03-03 16:30 ` szabolcs.nagy
2023-03-03 16:57 ` H.J. Lu
2023-03-03 17:39 ` szabolcs.nagy
2023-03-03 17:50 ` H.J. Lu
2023-03-03 17:41 ` Edgecombe, Rick P
2023-02-27 22:29 ` [PATCH v7 02/41] x86/shstk: Add Kconfig option for shadow stack Rick Edgecombe
2023-02-27 22:29 ` [PATCH v7 03/41] x86/cpufeatures: Add CPU feature flags for shadow stacks Rick Edgecombe
2023-02-27 22:29 ` [PATCH v7 04/41] x86/cpufeatures: Enable CET CR4 bit for shadow stack Rick Edgecombe
2023-02-27 22:29 ` [PATCH v7 05/41] x86/fpu/xstate: Introduce CET MSR and XSAVES supervisor states Rick Edgecombe
2023-02-27 22:29 ` [PATCH v7 06/41] x86/fpu: Add helper for modifying xstate Rick Edgecombe
2023-02-27 22:29 ` [PATCH v7 07/41] x86: Move control protection handler to separate file Rick Edgecombe
2023-03-01 15:38 ` Borislav Petkov
2023-02-27 22:29 ` [PATCH v7 08/41] x86/shstk: Add user control-protection fault handler Rick Edgecombe
2023-03-01 18:06 ` Borislav Petkov
2023-03-01 18:14 ` Edgecombe, Rick P
2023-03-01 18:37 ` Borislav Petkov
2023-02-27 22:29 ` [PATCH v7 09/41] x86/mm: Remove _PAGE_DIRTY from kernel RO pages Rick Edgecombe
2023-02-27 22:29 ` [PATCH v7 10/41] x86/mm: Move pmd_write(), pud_write() up in the file Rick Edgecombe
2023-02-27 22:29 ` [PATCH v7 11/41] mm: Introduce pte_mkwrite_kernel() Rick Edgecombe
2023-02-27 22:29 ` [PATCH v7 12/41] s390/mm: Introduce pmd_mkwrite_kernel() Rick Edgecombe
2023-02-27 22:29 ` [PATCH v7 13/41] mm: Make pte_mkwrite() take a VMA Rick Edgecombe
2023-03-01 7:03 ` Christophe Leroy
2023-03-01 8:16 ` David Hildenbrand
2023-03-02 12:19 ` Borislav Petkov
2023-02-27 22:29 ` [PATCH v7 14/41] x86/mm: Introduce _PAGE_SAVED_DIRTY Rick Edgecombe
2023-03-02 12:48 ` Borislav Petkov
2023-03-02 17:01 ` Edgecombe, Rick P
2023-02-27 22:29 ` [PATCH v7 15/41] x86/mm: Update ptep/pmdp_set_wrprotect() for _PAGE_SAVED_DIRTY Rick Edgecombe
2023-02-27 22:29 ` [PATCH v7 16/41] x86/mm: Start actually marking _PAGE_SAVED_DIRTY Rick Edgecombe
2023-02-27 22:29 ` [PATCH v7 17/41] mm: Move VM_UFFD_MINOR_BIT from 37 to 38 Rick Edgecombe
2023-02-27 22:29 ` [PATCH v7 18/41] mm: Introduce VM_SHADOW_STACK for shadow stack memory Rick Edgecombe
2023-02-27 22:29 ` [PATCH v7 19/41] x86/mm: Check shadow stack page fault errors Rick Edgecombe
2023-03-03 14:00 ` Borislav Petkov
2023-03-03 14:39 ` Dave Hansen
2023-02-27 22:29 ` [PATCH v7 20/41] x86/mm: Teach pte_mkwrite() about stack memory Rick Edgecombe
2023-03-03 15:37 ` Borislav Petkov
2023-02-27 22:29 ` [PATCH v7 21/41] mm: Add guard pages around a shadow stack Rick Edgecombe
2023-03-06 8:08 ` Borislav Petkov
2023-03-07 1:29 ` Edgecombe, Rick P
2023-03-07 10:32 ` Borislav Petkov
2023-03-07 10:44 ` David Hildenbrand
2023-03-08 22:48 ` Edgecombe, Rick P
2023-03-17 17:09 ` Deepak Gupta
2023-02-27 22:29 ` [PATCH v7 22/41] mm/mmap: Add shadow stack pages to memory accounting Rick Edgecombe
2023-03-06 13:01 ` Borislav Petkov
2023-03-06 18:11 ` Edgecombe, Rick P
2023-03-06 18:16 ` Borislav Petkov
2023-03-07 10:42 ` David Hildenbrand
2023-03-17 17:12 ` Deepak Gupta
2023-03-17 17:16 ` Dave Hansen
2023-03-17 17:28 ` Deepak Gupta
2023-03-17 17:42 ` Edgecombe, Rick P
2023-03-17 19:26 ` Deepak Gupta
2023-02-27 22:29 ` [PATCH v7 23/41] mm: Re-introduce vm_flags to do_mmap() Rick Edgecombe
2023-02-27 22:29 ` [PATCH v7 24/41] mm: Don't allow write GUPs to shadow stack memory Rick Edgecombe
2023-03-06 13:10 ` Borislav Petkov
2023-03-06 18:15 ` Andy Lutomirski
2023-03-06 18:33 ` Edgecombe, Rick P
2023-03-06 18:57 ` Andy Lutomirski
2023-03-07 1:47 ` Edgecombe, Rick P
2023-03-17 17:05 ` Deepak Gupta
2023-02-27 22:29 ` [PATCH v7 25/41] x86/mm: Introduce MAP_ABOVE4G Rick Edgecombe
2023-03-06 18:09 ` Borislav Petkov
2023-03-07 1:10 ` Edgecombe, Rick P
2023-02-27 22:29 ` [PATCH v7 26/41] mm: Warn on shadow stack memory in wrong vma Rick Edgecombe
2023-03-08 8:53 ` Borislav Petkov
2023-03-08 23:36 ` Edgecombe, Rick P
2023-02-27 22:29 ` [PATCH v7 27/41] x86/mm: Warn if create Write=0,Dirty=1 with raw prot Rick Edgecombe
2023-02-27 22:54 ` Kees Cook
2023-03-08 9:23 ` Borislav Petkov
2023-03-08 23:35 ` Edgecombe, Rick P
2023-02-27 22:29 ` [PATCH v7 28/41] x86: Introduce userspace API for shadow stack Rick Edgecombe
2023-03-08 10:27 ` Borislav Petkov
2023-03-08 23:32 ` Edgecombe, Rick P
2023-03-09 12:57 ` Borislav Petkov
2023-03-09 16:56 ` Edgecombe, Rick P
2023-03-09 23:51 ` Borislav Petkov
2023-03-10 1:13 ` Edgecombe, Rick P
2023-03-10 2:03 ` H.J. Lu [this message]
2023-03-10 20:00 ` H.J. Lu
2023-03-10 20:27 ` Edgecombe, Rick P
2023-03-10 20:43 ` H.J. Lu
2023-03-10 21:01 ` Edgecombe, Rick P
2023-03-10 11:40 ` Borislav Petkov
2023-02-27 22:29 ` [PATCH v7 29/41] x86/shstk: Add user-mode shadow stack support Rick Edgecombe
2023-02-27 22:29 ` [PATCH v7 30/41] x86/shstk: Handle thread shadow stack Rick Edgecombe
2023-03-02 17:34 ` Szabolcs Nagy
2023-03-02 21:48 ` Edgecombe, Rick P
2023-03-08 15:26 ` Borislav Petkov
2023-03-08 20:03 ` Edgecombe, Rick P
2023-03-09 14:12 ` Borislav Petkov
2023-03-09 16:59 ` Edgecombe, Rick P
2023-03-09 17:04 ` Borislav Petkov
2023-03-09 20:29 ` Edgecombe, Rick P
2023-02-27 22:29 ` [PATCH v7 31/41] x86/shstk: Introduce routines modifying shstk Rick Edgecombe
2023-03-09 16:48 ` Borislav Petkov
2023-03-09 17:03 ` Edgecombe, Rick P
2023-03-09 17:22 ` Borislav Petkov
2023-02-27 22:29 ` [PATCH v7 32/41] x86/shstk: Handle signals for shadow stack Rick Edgecombe
2023-03-09 17:02 ` Borislav Petkov
2023-03-09 17:16 ` Edgecombe, Rick P
2023-03-09 23:35 ` Borislav Petkov
2023-02-27 22:29 ` [PATCH v7 33/41] x86/shstk: Introduce map_shadow_stack syscall Rick Edgecombe
[not found] ` <ZADbP7HvyPHuwUY9@arm.com>
2023-03-02 21:21 ` Edgecombe, Rick P
2023-03-09 18:55 ` Deepak Gupta
2023-03-09 19:39 ` Edgecombe, Rick P
2023-03-09 21:08 ` Deepak Gupta
2023-03-10 0:14 ` Edgecombe, Rick P
2023-03-10 21:00 ` Deepak Gupta
2023-03-10 21:43 ` Edgecombe, Rick P
2023-03-16 20:07 ` Deepak Gupta
2023-03-14 7:19 ` Mike Rapoport
2023-03-16 19:30 ` Deepak Gupta
2023-03-10 16:11 ` Borislav Petkov
2023-03-10 17:12 ` Edgecombe, Rick P
2023-03-10 20:05 ` Borislav Petkov
2023-03-10 20:19 ` Edgecombe, Rick P
2023-03-10 20:26 ` Borislav Petkov
2023-02-27 22:29 ` [PATCH v7 34/41] x86/shstk: Support WRSS for userspace Rick Edgecombe
2023-03-10 16:44 ` Borislav Petkov
2023-03-10 17:16 ` Edgecombe, Rick P
2023-02-27 22:29 ` [PATCH v7 35/41] x86: Expose thread features in /proc/$PID/status Rick Edgecombe
2023-02-27 22:29 ` [PATCH v7 36/41] x86/shstk: Wire in shadow stack interface Rick Edgecombe
2023-02-27 22:29 ` [PATCH v7 37/41] selftests/x86: Add shadow stack test Rick Edgecombe
2023-02-27 22:29 ` [PATCH v7 38/41] x86/fpu: Add helper for initing features Rick Edgecombe
2023-03-11 12:54 ` Borislav Petkov
2023-03-13 2:45 ` Edgecombe, Rick P
2023-03-13 11:03 ` Borislav Petkov
2023-03-13 16:10 ` Edgecombe, Rick P
2023-03-13 17:10 ` Borislav Petkov
2023-03-13 23:31 ` Edgecombe, Rick P
2023-02-27 22:29 ` [PATCH v7 39/41] x86: Add PTRACE interface for shadow stack Rick Edgecombe
2023-03-11 15:06 ` Borislav Petkov
2023-03-13 2:53 ` Edgecombe, Rick P
2023-02-27 22:29 ` [PATCH v7 40/41] x86/shstk: Add ARCH_SHSTK_UNLOCK Rick Edgecombe
2023-03-11 15:11 ` Borislav Petkov
2023-03-13 3:04 ` Edgecombe, Rick P
2023-03-13 11:05 ` Borislav Petkov
2023-02-27 22:29 ` [PATCH v7 41/41] x86/shstk: Add ARCH_SHSTK_STATUS Rick Edgecombe
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