From: Florian Weimer <fweimer@redhat.com>
To: "H.J. Lu via Gcc-patches" <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH] x86: Document -mno-cet-switch
Date: Wed, 11 May 2022 10:12:22 +0200 [thread overview]
Message-ID: <87sfpgij2x.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <20220510162049.2686945-1-hjl.tools@gmail.com> (H. J. Lu via Gcc-patches's message of "Tue, 10 May 2022 09:20:49 -0700")
* H. J. Lu via Gcc-patches:
> When -fcf-protection=branch is used, the compiler will generate jump
> tables where the indirect jump is prefixed with the NOTRACK prefix, so
> it can jump to non-ENDBR targets. Yet, for NOTRACK prefixes to work, the
> NOTRACK specific enable bit must be set, what renders the binary broken
> on any environment where this is not the case. In fact, having NOTRACK
> disabled was a design choice for the Linux kernel CET support.
Why isn't that a kernel bug? It doesn't match what is in the current
glibc sources.
> Generate jump tables with ENDBR and skip the NOTRACK prefix for indirect
> jump. Document -mno-cet-switch to turn off CET instrumentation on jump
> tables for switch statements.
Of course, that is a slight regression in security hardening.
Quite frankly, I'm puzzled why the kernel decided to require these
additional ENDBR instructions.
Thanks,
Florian
next prev parent reply other threads:[~2022-05-11 8:12 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-10 16:20 H.J. Lu
2022-05-11 7:15 ` Uros Bizjak
2022-05-11 8:12 ` Florian Weimer [this message]
2022-05-11 14:20 ` H.J. Lu
2022-05-11 15:58 ` Florian Weimer
2022-05-11 18:00 ` H.J. Lu
2022-05-11 18:22 ` Florian Weimer
2022-05-11 18:36 ` H.J. Lu
2022-05-11 18:45 ` Florian Weimer
2022-05-11 18:57 ` H.J. Lu
2022-05-11 19:02 ` Florian Weimer
2022-05-11 20:04 ` H.J. Lu
2022-05-12 7:15 ` Richard Biener
2022-05-12 16:42 ` H.J. Lu
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