On Wed, 2019-06-26 at 10:14 -0700, Andy Lutomirski wrote: > On Thu, May 2, 2019 at 4:10 AM Dave Martin <Dave.Martin@xxxxxxx> wrote: > > > > On Wed, May 01, 2019 at 02:12:17PM -0700, Yu-cheng Yu wrote: > > > An ELF file's .note.gnu.property indicates features the executable file > > > can support. For example, the property GNU_PROPERTY_X86_FEATURE_1_AND > > > indicates the file supports GNU_PROPERTY_X86_FEATURE_1_IBT and/or > > > GNU_PROPERTY_X86_FEATURE_1_SHSTK. > > > [...] > > Where did PT_GNU_PROPERTY come from? Are there actual docs for it? > Can someone here tell us what the actual semantics of this new ELF > thingy are? From some searching, it seems like it's kind of an ELF > note but kind of not. An actual description would be fantastic. > > Also, I don't think there's any actual requirement that the upstream > kernel recognize existing CET-enabled RHEL 8 binaries as being > CET-enabled. I tend to think that RHEL 8 jumped the gun here. While > the upstream kernel should make some reasonble effort to make sure > that RHEL 8 binaries will continue to run, I don't see why we need to > go out of our way to keep the full set of mitigations available for > binaries that were developed against a non-upstream kernel. > > In fact, if we handle the legacy bitmap differently from RHEL 8, we > may *have* to make sure that we don't recognize existing RHEL 8 > binaries as CET-enabled. We have worked out the issue. Linux will look at only PT_GNU_PROPERTY, which is a shortcut pointing directly to .note.gnu.property. I have an updated patch, and will send it out (although it is not yet perfect). The Linux gABI extension draft is here: https://github.com/hjl-tools/linux-abi/w iki/linux-abi-draft.pdf. Yu-cheng
