Re: [syzbot] KASAN: stack-out-of-bounds Read in profile_pc

[Andi Kleen]

> profile_pc() assumes the return address is either directly at regs->sp,
> or one word adjacent to it due to saved flags, both of which are just
> completely wrong.  This code has probably never worked with ORC, and
> nobody noticed apparently.

I presume it used to work because the lock functions were really simple, 
but that's not true anymore.

> We could just use ORC to unwind to the next frame.  Though, isn't
> /proc/profile redundant, compared to all the more sophisticated options
> nowadays?  Is there still a distinct use case for it or can we just
> remove it?

It's still needed for some special cases. For example there is no other 
viable way to profile early boot without a VM

I would just drop the hack to unwind, at least for the early boot 
profile use case locking profiling is usually not needed.

-Andi