On Tue, Mar 18, 2025 at 03:56:36PM +0000, David Woodhouse wrote: > But on the whole, I'm not sure the CFI check is worth it. > > CFI checks that the caller and callee agree about the prototype of the > function being called. There are two main benefits of this: > > • to protect against attacks where function pointers are substituted > for gadgets. > > • to protect against genuine bugs, where the caller and the callee > disagree about the function arguments.
AFAIK the first one is the main point of CFI. > 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. > — 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? -- Josh
