On Thu, Nov 17, 2022 at 12:25:16PM +0000, Schimpe, Christina wrote: > > + Christina > > > > On Tue, 2022-11-15 at 15:43 +0100, Peter Zijlstra wrote: > > > On Fri, Nov 04, 2022 at 03:36:02PM -0700, Rick Edgecombe wrote: > > > > From: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx> > > > > > > > > Some applications (like GDB and CRIU) would like to tweak CET state > > > > via ptrace. This allows for existing functionality to continue to > > > > work for seized CET applications. Provide an interface based on the > > > > xsave buffer format of CET, but filter unneeded states to make the > > > > kernel’s job easier. > > > > > > > > There is already ptrace functionality for accessing xstate, but this > > > > does not include supervisor xfeatures. So there is not a completely > > > > clear place for where to put the CET state. Adding it to the user > > > > xfeatures regset would complicate that code, as it currently shares > > > > logic with signals which should not have supervisor features. > > > > > > > > Don’t add a general supervisor xfeature regset like the user one, > > > > because it is better to maintain flexibility for other supervisor > > > > xfeatures to define their own interface. For example, an xfeature > > > > may decide not to expose all of it’s state to userspace. A lot of > > > > enum values remain to be used, so just put it in dedicated CET > > > > regset. > > > > > > > > The only downside to not having a generic supervisor xfeature > > > > regset, is that apps need to be enlightened of any new supervisor > > > > xfeature exposed this way (i.e. they can’t try to have generic > > > > save/restore logic). But maybe that is a good thing, because they > > > > have to think through each new xfeature instead of encountering > > > > issues when new a new supervisor xfeature was added. > > > > > > Per this argument this should not use the CET XSAVE format and CET > > > name at all, because that conflates the situation vs IBT. Enabling > > > that might not want to follow this precedent. > > > > 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. This is about Shadow Stack -- IBT is a completely different feature and not subject of this series. Also, wth is an inferior call?
