Michael Schmitz <schmitzmic@xxxxxxxxx> writes: > m68k version of Eric's patch series 'alpha/ptrace: Improved > switch_stack handling'. > > Registers d6, d7, a3-a6 are not saved on the stack by default > on every syscall entry by the m68k kernel. A separate switch > stack frame is pushed to save those registers as needed. > This leaves the majority of syscalls with only a subset of > registers on the stack, and access to unsaved registers in > those would expose or modify random stack addresses. > > Patch 1 and 2 add a switch stack for all syscalls that were > found to need one to allow ptrace access to all registers > outside of syscall entry/exit tracing, as well as kernel > worker threads. This ought to protect against accidents. > > Patch 3 adds safety checks and debug output to m68k get_reg() > and put_reg() functions. Any unsafe register access during > process tracing will be prevented and reported. > > Suggestions for optimizations or improvements welcome! > > Cheers, > > Michael > > Link: https://lore.kernel.org/r/<87pmwlek8d.fsf_-_@disp2133> I have been digging into this some more and I have found one place that I am having a challenge dealing with. In arch/m68k/fpsp040/skeleton.S there is an assembly version of copy_from_user that calls fpsp040_die when the bytes can not be read. Now fpsp040_die is just: /* * This function is called if an error occur while accessing * user-space from the fpsp040 code. */ asmlinkage void fpsp040_die(void) { do_exit(SIGSEGV); } The problem here is the instruction emulation performed in the fpsp040 code performs a very minimal saving of registers. I don't think even the normal system call entry point registers that are saved are present at that point. Is there any chance you can help me figure out how to get a stack frame with all of the registers present before fpsp040_die is called? Eric
