linux-kernel - Re: [PATCH] x86/ibt: Implement FineIBT

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Message-ID: <CABCJKuc8eu0t08E0e1si-Sm2m0QqB1mrzofZy9cJ3G-tHBUZRg@mail.gmail.com>
Date:   Mon, 24 Oct 2022 10:15:59 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Josh Poimboeuf <jpoimboe@...nel.org>, x86@...nel.org,
        Kees Cook <keescook@...omium.org>,
        Joao Moreira <joao@...rdrivepizza.com>,
        linux-kernel@...r.kernel.org, Mark Rutland <mark.rutland@....com>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH] x86/ibt: Implement FineIBT

On Sat, Oct 22, 2022 at 8:03 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Fri, Oct 21, 2022 at 04:08:59PM -0700, Josh Poimboeuf wrote:
> > On Tue, Oct 18, 2022 at 03:35:50PM +0200, Peter Zijlstra wrote:
> > > +#ifdef CONFIG_FINEIBT
> > > +/*
> > > + * kCFI                                            FineIBT
> > > + *
> > > + * __cfi_\func:                                    __cfi_\func:
> > > + * movl   $0x12345678,%eax                      endbr64                    // 4
> > > + * nop                                          subl   $0x12345678,%r10d   // 7
> > > + * nop                                          jz     1f                  // 2
> > > + * nop                                          ud2                        // 2
> > > + * nop                                     1:   nop                        // 1
> > > + * nop
> > > + * nop
> > > + * nop
> > > + * nop
> > > + * nop
> > > + * nop
> > > + * nop
> >
> > All the "CFI" naming everywhere is very unfortunate.  We already have
> > "call frame information" in both the toolchain and objtool.
> >
> > The feature is called "kCFI" anyway, can Clang call the symbols
> > '__kcfi_*'?
>
> I think the compiler patch is already merged in clang, not sure that's
> still an option, Sami?

Yes, the compiler patch is already in, but if the cfi/kcfi confusion
is a big concern, it's still possible to rename the symbol before
Clang 16 is released. However, I thought we picked the __cfi prefix
earlier to make things less confusing with FineIBT? Joao, are you
still planning on adding FineIBT to Clang as well?

Sami