On 1/22/21 3:43 PM, Ard Biesheuvel wrote: > On Fri, 22 Jan 2021 at 22:15, Madhavan T. Venkataraman > <madvenka@xxxxxxxxxxxxxxxxxxx> wrote: >> >> >> >> On 1/22/21 11:43 AM, Mark Brown wrote: >>> On Thu, Jan 21, 2021 at 12:54:52PM -0600, Josh Poimboeuf wrote: >>> >>>> 2) The shadow stack idea sounds promising -- how hard would it be to >>>> make a prototype reliable unwinder? >>> >>> In theory it doesn't look too hard and I can't see a particular reason >>> not to try doing this - there's going to be edge cases but hopefully for >>> reliable stack trace they're all in areas where we would be happy to >>> just decide the stack isn't reliable anyway, things like nesting which >>> allocates separate shadow stacks for each nested level for example. >>> I'll take a look. >>> >> >> I am a new comer to this discussion and I am learning. Just have some >> questions. Pardon me if they are obvious or if they have already been >> asked and answered. >> >> Doesn't Clang already have support for a shadow stack implementation for ARM64? >> We could take a look at how Clang does it. >> >> Will there not be a significant performance hit? May be, some of it can be >> mitigated by using a parallel shadow stack rather than a compact one. >> >> Are there any longjmp style situations in the kernel where the stack is >> unwound by several frames? In these cases, the shadow stack must be unwound >> accordingly. >> > > Hello Madhavan, > > Let's discuss the details of shadow call stacks on a separate thread, > instead of further hijacking Julien's series. > OK. Sounds good.
