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

Sami Tolvanen
2022-05-17T20:26:40Z

On Tue, May 17, 2022 at 1:58 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Fri, May 13, 2022 at 01:21:38PM -0700, Sami Tolvanen wrote:
> > KCFI is a proposed forward-edge control-flow integrity scheme for
> > Clang, which is more suitable for kernel use than the existing CFI
> > scheme used by CONFIG_CFI_CLANG. KCFI doesn't require LTO, doesn't
> > alter function references to point to a jump table, and won't break
> > function address equality. The latest LLVM patch is here:
> >
> > https://reviews.llvm.org/D119296
> >
> > This RFC series replaces the current arm64 CFI implementation with
> > KCFI and adds support for x86_64.
>
> You have some weird behaviour vs weak functions (I so hate those)...
>
> 100: 0000000000000980 9 FUNC LOCAL DEFAULT 2 __cfi_free_initmem
> 233: 0000000000000989 35 FUNC WEAK DEFAULT 2 free_initmem
>
> With the result that on the final link:
>
> 179: 00000000000009b0 9 FUNC LOCAL DEFAULT 1 __cfi_free_initmem
> 8689: 00000000000007f0 9 FUNC LOCAL DEFAULT 65 __cfi_free_initmem
> 173283: 00000000000007f9 198 FUNC GLOBAL DEFAULT 65 free_initmem
>
> This is getting me objtool issues (I'll fix them) but perhaps it's
> something you can do something about as well.

Good catch, I'll fix this.

Sami