On Fri, 2022-11-18 at 16:21 +0000, Schimpe, Christina wrote: > > On Thu, 2022-11-17 at 12:25 +0000, Schimpe, Christina wrote: > > > > Hmm, we definitely need to be able to set the SSP. Christina, > > > > does > > > > GDB need anything else? I thought maybe toggling SHSTK_EN? > > > > > > In addition to the SSP, we want to write the CET state. For > > > instance > > > for inferior calls, we want to reset the IBT bits. > > > However, we won't write states that are disallowed by HW. > > > > Sorry, I should have given more background. Peter is saying we > > should split > > the ptrace interface so that shadow stack and IBT are separate. > > They would also no longer necessarily mirror the CET_U MSR format. > > Instead the kernel would expose a kernel specific format that has > > the > > needed bits of shadow stack support. And a separate one later for > > IBT. > > > > So the question is what does shadow stack need to support for > > ptrace > > besides SSP? Is it only SSP? The other features are SHSTK_EN and > > WRSS_EN. > > It might actually be nice to keep how these bits get flipped more > > controlled > > (remove them from ptrace). It looks like CRIU didn't need them. > > > > GDB currently reads the CET_U and SSP register. However, we don’t > necessarily have to read EB_LEG_BITMAP_BASE. > In addition to SSP, we want to write the bits for the IBT state > machine (TRACKER and SUPPRESS). > However, besides that GDB does not have to write anything else. Again, this is just about shadow stack. IBT will have a separate interface. So based on these comments, I'll change the interface in this patch to one for simply reading/writing SSP.
