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

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