Date: Thu, 30 Jul 2020 17:47:14 +0100 From: Szabolcs Nagy <szabolcs.nagy@....com> To: Jann Horn <jannh@...gle.com> Cc: Florian Weimer <fweimer@...hat.com>, oss-security@...ts.openwall.com, x86-64-abi@...glegroups.com, Kernel Hardening <kernel-hardening@...ts.openwall.com> Subject: Re: Alternative CET ABI The 07/30/2020 18:41, Jann Horn wrote: > On Thu, Jul 30, 2020 at 6:02 PM Florian Weimer <fweimer@...hat.com> 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 ld.so only needs to generate one plt entry for a function in a process and that entry can provided the canonical address that is loaded from some got entry when the address is used, so there is double indirection, but it works. > function pointers obtained through different shared libraries might > change? > > I guess you could maybe canonicalize function pointers somehow, but > that'd probably at least break dlclose(), right? IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.
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