On Fri, Jan 22, 2021 at 10:43:09PM +0100, 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. It's quite relevant to this thread. There's no need to consider merging Julien's patches if you have a better approach. Why not discuss it here? I'm also interested in the answers to Madhavan's questions. -- Josh
