linux-hardening - Re: [RFC PATCH 01/11] x86: kernel FineIBT

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Date:   Wed, 4 May 2022 17:28:57 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Peter Collingbourne <pcc@...gle.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Joao Moreira <joao@...rdrivepizza.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-hardening@...r.kernel.org, andrew.cooper3@...rix.com,
        Kees Cook <keescook@...omium.org>,
        Mark Rutland <mark.rutland@....com>, hjl.tools@...il.com,
        alyssa.milburn@...ux.intel.com,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        gabriel.gomes@...ux.intel.com, rick.p.edgecombe@...el.com
Subject: Re: [RFC PATCH 01/11] x86: kernel FineIBT

On Wed, May 4, 2022 at 11:17 AM Peter Zijlstra <peterz@...radead.org> wrote:
> __cfi_\sym:                                     __cfi_\sym:
>                                                         int3; int3                              # 2
>         endbr                   # 4                     mov     \hash, %eax                     # 5
>         call    __fineibt_\hash # 5                     int3; int3                              # 2
> \sym:                                           \sym:

OK, that looks reasonable to me.

> It seems to preserve the properties of the last one in that direct calls
> will already be correct and we don't need linker fixups, and objtool can
> simply parse the preamble as regular instructions without needing
> further help.

Wouldn't objtool still print out unreachable instruction warnings here?

Sami