On Wed, May 11, 2022 at 1:12 AM Florian Weimer <fwei...@redhat.com> wrote: > > * H. J. Lu via Gcc-patches: > > > When -fcf-protection=branch is used, the compiler will generate jump > > tables where the indirect jump is prefixed with the NOTRACK prefix, so > > it can jump to non-ENDBR targets. Yet, for NOTRACK prefixes to work, the > > NOTRACK specific enable bit must be set, what renders the binary broken > > on any environment where this is not the case. In fact, having NOTRACK > > disabled was a design choice for the Linux kernel CET support. > > Why isn't that a kernel bug? It doesn't match what is in the current > glibc sources.
User space uses NOTRACK in the jump table in assembly codes. > > Generate jump tables with ENDBR and skip the NOTRACK prefix for indirect > > jump. Document -mno-cet-switch to turn off CET instrumentation on jump > > tables for switch statements. > > Of course, that is a slight regression in security hardening. > > Quite frankly, I'm puzzled why the kernel decided to require these > additional ENDBR instructions. Kernel is using -mcet-switch today. Should we document -mcet-switch and keep it off by default instead? -- H.J.
