linux-hardening - Re: [RFC PATCH 21/21] x86: Add support for CONFIG_CFI

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Date:   Mon, 2 May 2022 08:20:05 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>, X86 ML <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>,
        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 21/21] x86: Add support for CONFIG_CFI_CLANG

On Sat, Apr 30, 2022 at 2:24 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Fri, Apr 29, 2022 at 01:36:44PM -0700, Sami Tolvanen wrote:
> > -     if (report_bug(regs->ip, regs) == BUG_TRAP_TYPE_WARN) {
> > +     if (report_bug(regs->ip, regs) == BUG_TRAP_TYPE_WARN ||
> > +         report_cfi(regs->ip, regs) == BUG_TRAP_TYPE_WARN) {
>
> This way you'll first get a BUG splat and then tack on the CFI thing.

The CFI ud2 isn't in the bug table, which means find_bug returns
BUG_TRAP_TYPE_NONE and report_bug bails out before printing out
anything.

Sami