linux-kernel - Re: [RFC] Circumventing FineIBT Via Entrypoints

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Message-ID: <20250217185444.GB7304@noisy.programming.kicks-ass.net>
Date: Mon, 17 Feb 2025 19:54:44 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: David Laight <david.laight.linux@...il.com>
Cc: Kees Cook <kees@...nel.org>, Andrew Cooper <andrew.cooper3@...rix.com>,
	jannh@...gle.com, jmill@....edu, joao@...rdrivepizza.com,
	linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org,
	luto@...nel.org, samitolvanen@...gle.com,
	scott.d.constable@...el.com, x86@...nel.org
Subject: Re: [RFC] Circumventing FineIBT Via Entrypoints

On Mon, Feb 17, 2025 at 06:38:27PM +0000, David Laight wrote:

> I may not have retpolines enabled, a typical call site is (from vmlinux.o):

Make sure CONFIG_FINEIBT=y, otherwise there is no point in talking about
this. This requires KERNEL_IBT=y RETPOLINE=y CALL_PADDING=y CFI_CLANG=y.

Then look at arch/x86/include/asm/cfi.h and make sure to read the
comment, and then read arch/x86/kernel/alternative.c:__apply_fineibt().

Which ever way around you're going to turn this, you'll never find the
fineibt code in the object files.