Re: [PATCH 0/3] ABI CHANGE!!! Remove questionable remote SP reads

From: Raymond Jennings
Date: Tue Oct 04 2016 - 03:07:07 EST

My personal opinion is that even looking at esp/rsp is asking for trouble. The only reliable information is VM_STACK or another VM flag that makes the area expand in response to stack growth.

Besides, userspace could always play funky trampoline games with the stack pointer, or even dynamically expand the stack by doing a malloc if a stack overflow draws near, which would put the stack in the data section temporarily.

As long as esp is in the bounds of a valid VMA, my vote is that we should consider it undefined how the task uses it.

On Mon, Oct 3, 2016 at 4:17 PM, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
On Mon, Oct 3, 2016 at 4:08 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:


We need to decide fairly soon whether to apply these (or perhaps just
patch 1 or just patches 2 and 3) for 4.9. For any parts that aren't
applied, I'll send quick fixups to pin the stack in the offending

I think we should apply it. Hopefully nothing uses it, and nobody will
notice. And if somebody *does* notice, the sooner we find out, the