On Thu, Jun 7, 2018 at 9:22 PM H.J. Lu <hjl.tools@xxxxxxxxx> wrote: > > On Thu, Jun 7, 2018 at 3:02 PM, H.J. Lu <hjl.tools@xxxxxxxxx> wrote: > > On Thu, Jun 7, 2018 at 2:01 PM, Andy Lutomirski <luto@xxxxxxxxxx> wrote: > >> On Thu, Jun 7, 2018 at 1:33 PM Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx> 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@xxxxxxxxx> 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: Is there any reason you can't use LD_CET=force to do it for dynamically linked binaries? I find it quite hard to believe that forcibly CET-ifying a legacy statically linked binary is a good idea.
