linux-hardening - Re: [RFC PATCH v2 00/21] KCFI support

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Date:   Mon, 16 May 2022 10:57:15 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     sedat.dilek@...il.com
Cc:     linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Joao Moreira <joao@...rdrivepizza.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-hardening@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, llvm@...ts.linux.dev
Subject: Re: [RFC PATCH v2 00/21] KCFI support

On Mon, May 16, 2022 at 10:31 AM Sedat Dilek <sedat.dilek@...il.com> wrote:
>> Anything Like LLVM cmake Options to be condidered and Set?
>
>
> I activate Clang and LLD ad projects - OK - enough?

Clang and LLD should be sufficient.

>> This series is also available in GitHub:
>>
>>   https://github.com/samitolvanen/linux/commits/kcfi-rfc-v2
>>
>>
>>
>
>> Can you please add a history of what changed?

Oops, I forgot to include that.

Changes in v2:
- Changed the compiler patch to encode arm64 target and type details
in the ESR, and updated the kernel error handling patch accordingly.
- Changed the compiler patch to embed the x86_64 type hash in a valid
instruction to avoid special casing objtool instruction decoding, and
added a __cfi_ symbol for the preamble. Changed the kernel error
handling and manual type annotations to match.
- Dropped the .kcfi_types section as that’s no longer needed by
objtool, and changed the objtool patch to simply ignore the __cfi_
preambles falling through.
- Dropped the .kcfi_traps section on arm64 as it’s no longer needed,
and moved the trap look-up code behind CONFIG_ARCH_USES_CFI_TRAPS,
which is selected only for x86_64.
- Dropped __nocfi attributes from arm64 code where CFI was disabled
due to address space confusion issues, and added type annotations to
relevant assembly functions.
- Dropped __nocfi from __init.

> Nathan has a i915 cfi patch in His personal kernel.org Git.
> Is this relevant to kcfi?

It fixes a type mismatch, so in that sense it's relevant.

> To distinguish between clang-cfi we should use different kbuild variables for kcfi.

The plan is to replace the current CFI implementation. Does reusing
the kbuild variable names cause a problem?

Sami