Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Tue, 18 Oct 2022 23:09:23 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Kees Cook <keescook@chromium.org>
Cc:     x86@kernel.org, Sami Tolvanen <samitolvanen@google.com>,
        Joao Moreira <joao@overdrivepizza.com>,
        linux-kernel@vger.kernel.org, Mark Rutland <mark.rutland@arm.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: [PATCH] x86/ibt: Implement FineIBT
Message-ID: <Y08WA+jFRNaH0eTQ@hirez.programming.kicks-ass.net>
References: <Y06rtoE9BsERG9uv@hirez.programming.kicks-ass.net>
 <202210181020.79AF7F7@keescook>
 <Y08FhjK3fKsfRAaw@hirez.programming.kicks-ass.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <Y08FhjK3fKsfRAaw@hirez.programming.kicks-ass.net>
Precedence: bulk

On Tue, Oct 18, 2022 at 09:59:02PM +0200, Peter Zijlstra wrote:

> @@ -732,6 +734,8 @@ static __init int cfi_parse_cmdline(char
>  			cfi_mode = CFI_KCFI;
>  		} else if (!strcmp(str, "fineibt")) {
>  			cfi_mode = CFI_FINEIBT;
> +		} else if (!strcmp(str, "norand")) {
> +			cfi_rand = false;
>  		} else {
>  			pr_err("Ignoring unknown cfi option (%s).", str);
>  		}

Plus so I suppose, otherwise it'll still randomize the hashes even if it
then leaves the whole thing disabled, which seems a bit daft :-)

Index: linux-2.6/arch/x86/kernel/alternative.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/alternative.c
+++ linux-2.6/arch/x86/kernel/alternative.c
@@ -730,6 +730,7 @@ static __init int cfi_parse_cmdline(char
 			cfi_mode = CFI_DEFAULT;
 		} else if (!strcmp(str, "off")) {
 			cfi_mode = CFI_OFF;
+			cfi_rand = false;
 		} else if (!strcmp(str, "kcfi")) {
 			cfi_mode = CFI_KCFI;
 		} else if (!strcmp(str, "fineibt")) {