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Date: Thu, 30 Jul 2020 18:41:40 +0200
From: Jann Horn <>
To: Florian Weimer <>
	Kernel Hardening <>, Szabolcs Nagy <>
Subject: Re: Alternative CET ABI

On Thu, Jul 30, 2020 at 6:02 PM Florian Weimer <> wrote:
> Functions no longer start with the ENDBR64 prefix.  Instead, the link
> editor produces a PLT entry with an ENDBR64 prefix if it detects any
> address-significant relocation for it.  The PLT entry performs a NOTRACK
> jump to the target address.  This assumes that the target address is
> subject to RELRO, of course, so that redirection is not possible.
> Without address-significant relocations, the link editor produces a PLT
> entry without the ENDBR64 prefix (but still with the NOTRACK jump), or
> perhaps no PLT entry at all.

How would this interact with function pointer comparisons? As in, if
library A exports a function func1 without referencing it, and
libraries B and C both take references to func1, would they end up
with different function pointers (pointing to their respective PLT
entries)? Would this mean that the behavior of a program that compares
function pointers obtained through different shared libraries might

I guess you could maybe canonicalize function pointers somehow, but
that'd probably at least break dlclose(), right?

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