linux-hardening - Re: [PATCH v2 5/5] crypto: x86/crc32c - Tweak jump table to validate objtool logic

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Message-ID: <20241010203401.45ds362dpx52ne5z@treble>
Date: Thu, 10 Oct 2024 13:34:01 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Ard Biesheuvel <ardb+git@...gle.com>
Cc: linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
	keescook@...omium.org, linux-hardening@...r.kernel.org,
	nathan@...nel.org, Ard Biesheuvel <ardb@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Jan Beulich <jbeulich@...e.com>,
	"Jose E. Marchesi" <jemarch@....org>, Kees Cook <kees@...nel.org>
Subject: Re: [PATCH v2 5/5] crypto: x86/crc32c - Tweak jump table to validate
 objtool logic

On Thu, Oct 10, 2024 at 02:28:07PM +0200, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@...nel.org>
> 
> Tweak the jump table so
> - the address is taken far way from its use
> - its offset from the start of .rodata is != 0x0
> - its type is STT_OBJECT and its size is set to the size of the actual
>   table
> - the indirect jump is annotated with a R_X86_64_NONE relocation
>   pointing to the jump table
> 
> Signed-off-by: Ard Biesheuvel <ardb@...nel.org>

This needs more "why", I assume the goals are to add the annotations +
confuse objtool if it doesn't read them properly?

-- 
Josh