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References: <20220513202159.1550547-1-samitolvanen@google.com>
 <20220513202159.1550547-21-samitolvanen@google.com> <202205141501.92A22264B4@keescook>
In-Reply-To: <202205141501.92A22264B4@keescook>
From:   Sami Tolvanen <samitolvanen@google.com>
Date:   Mon, 16 May 2022 11:57:16 -0700
Message-ID: <CABCJKudiLBjsNHUTH6zqhYik0WQZwsM4OceYJadYKoDQYOFRXw@mail.gmail.com>
Subject: Re: [RFC PATCH v2 20/21] x86: Add support for CONFIG_CFI_CLANG
To:     Kees Cook <keescook@chromium.org>
Cc:     linux-kernel@vger.kernel.org, Josh Poimboeuf <jpoimboe@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>, x86@kernel.org,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Joao Moreira <joao@overdrivepizza.com>,
        Sedat Dilek <sedat.dilek@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        linux-hardening@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, llvm@lists.linux.dev
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On Sat, May 14, 2022 at 3:03 PM Kees Cook <keescook@chromium.org> wrote:
>
> On Fri, May 13, 2022 at 01:21:58PM -0700, Sami Tolvanen wrote:
> > +#ifdef CONFIG_CFI_CLANG
> > +static void decode_cfi_insn(struct pt_regs *regs, unsigned long *target,
> > +                         unsigned long *type)
> > +{
> > +     char buffer[MAX_INSN_SIZE];
> > +     struct insn insn;
> > +     int offset;
> > +
> > +     *target = *type = 0;
>
> Should report_cfi_failure() have some additional hinting for the case
> where target/type are zero? Like, "hey, got an inexplicable CFI failure
> here, but preamble decode failed. Yikes!"

Good point, I'll add an error message here.

Sami