On 25/09/2024 5:45 pm, Ard Biesheuvel wrote: > On Wed, 25 Sept 2024 at 18:39, Linus Torvalds > <torva...@linux-foundation.org> wrote: >> And we do have special calling conventions that aren't the regular >> ones, so %rdi might actually be used elsewhere. For example, >> __get_user_X and __put_user_X all have magical calling conventions: >> they don't actually use %rdi, but part of the calling convention is >> that the unused registers aren't modified. >> >> Of course, I'm not actually sure you can probe those and trigger this >> issue, but it all makes me think it's broken. >> >> And it's entirely possible that I'm wrong for some reason, but this >> just _looks_ very very wrong to me. >> >> I think you can do this with a "pushq mem" instead, and put the >> relocation into the memory location. >> > I'll change this into > > pushq arch_rethook_trampoline@GOTPCREL(%rip) > > which I had originally. I was trying to avoid the load from memory, > but that obviously only works if the register is not live.
But does that work? Won't that will push the 8 bytes from the start of arch_rethook_trampoline, when what's wanted is simply the address of arch_rethook_trampoline itself. ~Andrew
