On Tue, Mar 18, 2025 at 09:06:58PM +0000, David Woodhouse wrote: > On Tue, 2025-03-18 at 10:14 -0700, Josh Poimboeuf wrote: > > On Tue, Mar 18, 2025 at 03:56:36PM +0000, David Woodhouse wrote: > > > For the relocate_kernel() case I don't think we care much about the > > > first. Without a CFI prologue, no *other* code can be tricked into > > > calling relocate_kernel() > > > > But for FineIBT the hash is checked on the callee side. So it loses > > FineIBT protection. > > Right now the relocate_kernel() code doesn't even have an endbr, does > it? So it isn't a useful gadget? In that case wouldn't IBT explode when you indirect call it? Or is IBT getting disabled beforehand? > > > — and besides, it's in the kernel's data > > > section and isn't executable anyway until the kexec code copies it to a > > > page that *is*. > > > > Does the code get copied immediately before getting called, or can it be > > initialized earlier during boot when kdump does its initial setup? > > It's initialized earlier, in machine_kexec_prepare(), and then the page > is set ROX. If that happens during boot (like for kdump init) then it'll be in text the whole time after boot, right? -- Josh
