On 8/24/22 11:48, Borislav Petkov wrote: > On Wed, Aug 24, 2022 at 11:43:10AM -0700, Dave Hansen wrote: >> So, we don't have *ANY* control over where the compiler uses jump >> tables. The kernel just happened to add some code that uses them, fell >> over, and this adds a hack to get booting again. >> >> Isn't this a bigger problem? > I had the same question already. Was thinking of maybe disabling > the compiler from producing jump tables in the ident-mapped code. > Tom's argument is that that might prevent the compiler from doing > optimizations but I haven't talked to compiler folks whether those > optimizations are even worth the effort. > > Regardless, the potential problem is limited: > > "# (jump-tables are implicitly disabled by RETPOLINE)" Ahh, I missed the connection with retpoline. The ubiquity of RETPOLINE=y probably means we'll see more of these issues because people won't find them unless they're building and running weirdo configurations. > i.e., only RETPOLINE=n builds for now which should be a minority? > > I guess when this explodes somewhere else again, we will have to > generalize a fix. Yep. It also reminds me to add RETPOLINE=n build to my tests.
