Messages in this thread | | | From | "H.J. Lu" <> | Date | Thu, 7 Jun 2018 21:22:13 -0700 | Subject | Re: [PATCH 06/10] x86/cet: Add arch_prctl functions for shadow stack |
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On Thu, Jun 7, 2018 at 3:02 PM, H.J. Lu <hjl.tools@gmail.com> wrote: > On Thu, Jun 7, 2018 at 2:01 PM, Andy Lutomirski <luto@kernel.org> wrote: >> On Thu, Jun 7, 2018 at 1:33 PM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote: >>> >>> On Thu, 2018-06-07 at 11:48 -0700, Andy Lutomirski wrote: >>> > On Thu, Jun 7, 2018 at 7:41 AM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote: >>> > > >>> > > The following operations are provided. >>> > > >>> > > ARCH_CET_STATUS: >>> > > return the current CET status >>> > > >>> > > ARCH_CET_DISABLE: >>> > > disable CET features >>> > > >>> > > ARCH_CET_LOCK: >>> > > lock out CET features >>> > > >>> > > ARCH_CET_EXEC: >>> > > set CET features for exec() >>> > > >>> > > ARCH_CET_ALLOC_SHSTK: >>> > > allocate a new shadow stack >>> > > >>> > > ARCH_CET_PUSH_SHSTK: >>> > > put a return address on shadow stack >>> > >
>> And why do we need ARCH_CET_EXEC? >> >> For background, I really really dislike adding new state that persists >> across exec(). It's nice to get as close to a clean slate as possible >> after exec() so that programs can run in a predictable environment. >> exec() is also a security boundary, and anything a task can do to >> affect itself after exec() needs to have its security implications >> considered very carefully. (As a trivial example, you should not be >> able to use cetcmd ... sudo [malicious options here] to cause sudo to >> run with CET off and then try to exploit it via the malicious options. >> >> If a shutoff is needed for testing, how about teaching ld.so to parse >> LD_CET=no or similar and protect it the same way as LD_PRELOAD is >> protected. Or just do LD_PRELOAD=/lib/libdoesntsupportcet.so. >> > > I will take a look.
We can use LD_CET to turn off CET. Since most of legacy binaries are compatible with shadow stack, ARCH_CET_EXEC can be used to turn on shadow stack on legacy binaries:
[hjl@gnu-cet-1 glibc]$ readelf -n /bin/ls| head -10
Displaying notes found in: .note.ABI-tag Owner Data size Description GNU 0x00000010 NT_GNU_ABI_TAG (ABI version tag) OS: Linux, ABI: 3.2.0
Displaying notes found in: .note.gnu.property Owner Data size Description GNU 0x00000020 NT_GNU_PROPERTY_TYPE_0 Properties: x86 ISA used: [hjl@gnu-cet-1 glibc]$ cetcmd --on -- /bin/ls / Segmentation fault [hjl@gnu-cet-1 glibc]$ cetcmd --on -f shstk -- /bin/ls / bin dev export lib libx32 media mnt opt root sbin sys usr boot etc home lib64 lost+found misc net proc run srv tmp var [hjl@gnu-cet-1 glibc]$ cetcmd --on -f ibt -- /bin/ls / Segmentation fault [hjl@gnu-cet-1 glibc]$
-- H.J.
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