On Thu, Nov 17, 2022 at 07:57:59PM +0000, Edgecombe, Rick P 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. CRIU reads CET_U with ptrace(PTRACE_GETREGSET, NT_X86_CET). It's done before the injection of the parasite. The value of SHSTK_EN is used then to detect if shadow stack is enabled and to setup victim's shadow stack for sigreturn. -- Sincerely yours, Mike.
