From: Andy Lutomirski <luto@amacapital.net>
To: Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>,
Peter Zijlstra <peterz@infradead.org>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
linux-mm@kvack.org, linux-arch@vger.kernel.org,
linux-api@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
Balbir Singh <bsingharora@gmail.com>,
Borislav Petkov <bp@alien8.de>,
Cyrill Gorcunov <gorcunov@gmail.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Eugene Syromiatnikov <esyr@redhat.com>,
Florian Weimer <fweimer@redhat.com>,
"H.J. Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>,
Jonathan Corbet <corbet@lwn.net>,
Kees Cook <keescook@chromium.org>,
Mike Kravetz <mike.kravetz@oracle.com>,
Nadav Amit <nadav.amit@gmail.com>,
Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
Randy Dunlap <rdunlap@infradead.org>,
"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>,
Dave Martin <Dave.Martin@arm.com>
Subject: Re: [PATCH v7 03/14] x86/cet/ibt: Add IBT legacy code bitmap setup function
Date: Fri, 7 Jun 2019 13:43:15 -0700 [thread overview]
Message-ID: <25281DB3-FCE4-40C2-BADB-B3B05C5F8DD3@amacapital.net> (raw)
In-Reply-To: <7e0b97bf1fbe6ff20653a8e4e147c6285cc5552d.camel@intel.com>
> On Jun 7, 2019, at 12:49 PM, Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
>
> On Fri, 2019-06-07 at 11:29 -0700, Andy Lutomirski wrote:
>>> On Jun 7, 2019, at 10:59 AM, Dave Hansen <dave.hansen@intel.com> wrote:
>>>
>>>> On 6/7/19 10:43 AM, Peter Zijlstra wrote:
>>>> I've no idea what the kernel should do; since you failed to answer the
>>>> question what happens when you point this to garbage.
>>>>
>>>> Does it then fault or what?
>>>
>>> Yeah, I think you'll fault with a rather mysterious CR2 value since
>>> you'll go look at the instruction that faulted and not see any
>>> references to the CR2 value.
>>>
>>> I think this new MSR probably needs to get included in oops output when
>>> CET is enabled.
>>
>> This shouldn’t be able to OOPS because it only happens at CPL 3, right? We
>> should put it into core dumps, though.
>>
>>>
>>> Why don't we require that a VMA be in place for the entire bitmap?
>>> Don't we need a "get" prctl function too in case something like a JIT is
>>> running and needs to find the location of this bitmap to set bits itself?
>>>
>>> Or, do we just go whole-hog and have the kernel manage the bitmap
>>> itself. Our interface here could be:
>>>
>>> prctl(PR_MARK_CODE_AS_LEGACY, start, size);
>>>
>>> and then have the kernel allocate and set the bitmap for those code
>>> locations.
>>
>> Given that the format depends on the VA size, this might be a good idea. I
>> bet we can reuse the special mapping infrastructure for this — the VMA could
>> be a MAP_PRIVATE special mapping named [cet_legacy_bitmap] or similar, and we
>> can even make special rules to core dump it intelligently if needed. And we
>> can make mremap() on it work correctly if anyone (CRIU?) cares.
>>
>> Hmm. Can we be creative and skip populating it with zeros? The CPU should
>> only ever touch a page if we miss an ENDBR on it, so, in normal operation, we
>> don’t need anything to be there. We could try to prevent anyone from
>> *reading* it outside of ENDBR tracking if we want to avoid people accidentally
>> wasting lots of memory by forcing it to be fully populated when the read it.
>>
>> The one downside is this forces it to be per-mm, but that seems like a
>> generally reasonable model anyway.
>>
>> This also gives us an excellent opportunity to make it read-only as seen from
>> userspace to prevent exploits from just poking it full of ones before
>> redirecting execution.
>
> GLIBC sets bits only for legacy code, and then makes the bitmap read-only. That
> avoids most issues:
How does glibc know the linear address space size? We don’t want LA64 to break old binaries because the address calculation changed.
next prev parent reply other threads:[~2019-06-07 20:46 UTC|newest]
Thread overview: 72+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-06 20:09 [PATCH v7 00/14] Control-flow Enforcement: Branch Tracking, PTRACE Yu-cheng Yu
2019-06-06 20:09 ` [PATCH v7 01/14] x86/cet/ibt: Add Kconfig option for user-mode Indirect Branch Tracking Yu-cheng Yu
2019-06-06 20:09 ` [PATCH v7 02/14] x86/cet/ibt: User-mode indirect branch tracking support Yu-cheng Yu
2019-06-06 20:09 ` [PATCH v7 03/14] x86/cet/ibt: Add IBT legacy code bitmap setup function Yu-cheng Yu
2019-06-07 8:08 ` Peter Zijlstra
2019-06-07 16:23 ` Yu-cheng Yu
2019-06-07 16:35 ` Andy Lutomirski
2019-06-07 16:39 ` Dave Hansen
2019-06-07 16:45 ` Yu-cheng Yu
2019-06-07 17:05 ` Andy Lutomirski
2019-06-07 17:43 ` Peter Zijlstra
2019-06-07 17:59 ` Dave Hansen
2019-06-07 18:29 ` Andy Lutomirski
2019-06-07 18:58 ` Dave Hansen
2019-06-07 19:56 ` Yu-cheng Yu
2019-06-07 20:40 ` Andy Lutomirski
2019-06-07 21:05 ` Dave Hansen
2019-06-07 19:49 ` Yu-cheng Yu
2019-06-07 20:00 ` Dave Hansen
2019-06-07 20:06 ` Yu-cheng Yu
2019-06-07 21:09 ` Dave Hansen
2019-06-07 22:27 ` Andy Lutomirski
2019-06-10 16:03 ` Yu-cheng Yu
2019-06-10 16:05 ` Yu-cheng Yu
2019-06-10 17:28 ` Florian Weimer
2019-06-10 17:59 ` Dave Hansen
2019-06-07 20:43 ` Andy Lutomirski [this message]
2019-06-10 15:22 ` Yu-cheng Yu
2019-06-10 18:02 ` Dave Hansen
2019-06-10 19:38 ` Yu-cheng Yu
2019-06-10 19:52 ` Dave Hansen
2019-06-10 19:55 ` Andy Lutomirski
2019-06-10 20:27 ` Yu-cheng Yu
2019-06-10 20:43 ` Dave Hansen
2019-06-10 20:58 ` Yu-cheng Yu
2019-06-10 22:02 ` Dave Hansen
2019-06-10 22:40 ` Yu-cheng Yu
2019-06-10 22:59 ` Dave Hansen
2019-06-10 23:20 ` H.J. Lu
2019-06-10 23:37 ` Dave Hansen
2019-06-10 23:54 ` Andy Lutomirski
2019-06-11 0:08 ` Dave Hansen
2019-06-11 0:36 ` Andy Lutomirski
2019-06-14 15:25 ` Yu-cheng Yu
2019-06-14 16:13 ` Dave Hansen
2019-06-14 17:13 ` Yu-cheng Yu
2019-06-14 20:57 ` Dave Hansen
2019-06-14 21:34 ` Yu-cheng Yu
2019-06-14 22:06 ` Dave Hansen
2019-06-15 15:30 ` Andy Lutomirski
2019-06-11 7:24 ` Florian Weimer
2019-06-08 20:52 ` Pavel Machek
2019-06-10 15:47 ` Yu-cheng Yu
2019-06-11 10:33 ` Pavel Machek
2019-06-07 19:03 ` Dave Hansen
2019-06-07 19:23 ` Yu-cheng Yu
2019-06-06 20:09 ` [PATCH v7 04/14] x86/cet/ibt: Handle signals for IBT Yu-cheng Yu
2019-06-06 20:09 ` [PATCH v7 05/14] mm/mmap: Add IBT bitmap size to address space limit check Yu-cheng Yu
2019-06-06 20:09 ` [PATCH v7 06/14] x86/cet/ibt: ELF header parsing for IBT Yu-cheng Yu
2019-06-06 20:09 ` [PATCH v7 07/14] x86/cet/ibt: Add arch_prctl functions " Yu-cheng Yu
2019-06-07 8:07 ` Peter Zijlstra
2019-06-06 20:09 ` [PATCH v7 08/14] x86/cet/ibt: Add ENDBR to op-code-map Yu-cheng Yu
2019-06-06 20:09 ` [PATCH v7 09/14] x86/vdso: Insert endbr32/endbr64 to vDSO Yu-cheng Yu
2019-06-06 20:26 ` Andy Lutomirski
2019-06-06 20:09 ` [PATCH v7 10/14] x86/vdso/32: Add ENDBR32 to __kernel_vsyscall entry point Yu-cheng Yu
2019-06-06 20:25 ` Andy Lutomirski
2019-06-06 20:09 ` [PATCH v7 11/14] x86/vsyscall/64: Add ENDBR64 to vsyscall entry points Yu-cheng Yu
2019-06-06 20:28 ` Andy Lutomirski
2019-06-06 20:09 ` [PATCH v7 12/14] x86/vsyscall/64: Fixup shadow stack and branch tracking for vsyscall Yu-cheng Yu
2019-06-06 20:27 ` Andy Lutomirski
2019-06-06 20:09 ` [PATCH v7 13/14] x86/cet: Add PTRACE interface for CET Yu-cheng Yu
2019-06-06 20:09 ` [PATCH v7 14/14] x86: Discard .note.gnu.property sections Yu-cheng Yu
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