linux-hardening - Re: [RFC PATCH 10/21] treewide: Drop function

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Date:   Thu, 5 May 2022 09:51:39 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>, X86 ML <x86@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Joao Moreira <joao@...rdrivepizza.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-hardening@...r.kernel.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        llvm@...ts.linux.dev
Subject: Re: [RFC PATCH 10/21] treewide: Drop function_nocfi

On Thu, May 5, 2022 at 9:30 AM Mark Rutland <mark.rutland@....com> wrote:
> I also believe that in most cases we can drop the __nocfi annotation on callers
> now that we can mark the called assembly function with SYM_TYPED_FUNC_START().

Good point, thanks for pointing that out. I'll add these to the next
version of the series.

> There' a latent bug here with the existing CFI scheme, since
> `kpti_install_ng_mappings` isn't marked with __nocfi, and should explode when
> calling `idmap_kpti_install_ng_mappings` via the idmap.

The CONFIG_UNMAP_KERNEL_AT_EL0 version of kpti_install_ng_mappings is
marked __nocfi

> There' a latent bug here with the existing CFI scheme, since
> `machine_kexec` isn't marked with __nocfi, and should explode when calling
> `cpu_soft_restart` via the idmap.

But it's indeed missing from this one.

Sami