linux-hardening - Re: [PATCH] randstruct: temporarily disable clang support

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Date:   Tue, 7 Feb 2023 10:01:21 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     Kees Cook <keescook@...omium.org>, linux-hardening@...r.kernel.org,
        llvm@...ts.linux.dev, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, Bill Wendling <morbo@...gle.com>
Subject: Re: [PATCH] randstruct: temporarily disable clang support

On Mon, Feb 6, 2023 at 3:41 PM Fangrui Song <maskray@...gle.com> wrote:
>
> On Sat, Feb 4, 2023 at 11:06 AM Kees Cook <keescook@...omium.org> wrote:
> >
> > On Fri, Feb 03, 2023 at 11:42:01AM -0800, Eric Biggers wrote:
> > > From: Eric Biggers <ebiggers@...gle.com>
> > >
> > > Randstruct with clang is currently unsafe to use in any clang release
> > > that supports it, due to a clang bug that is causing miscompilations:
> > > "-frandomize-layout-seed inconsistently randomizes all-function-pointers
> > > structs" (https://github.com/llvm/llvm-project/issues/60349).  Disable
> > > it temporarily until the bug is fixed and the fix is released in a clang
> > > version that can be checked for.
> > >
> > > Fixes: 035f7f87b729 ("randstruct: Enable Clang support")
> > > Cc: stable@...r.kernel.org
> > > Signed-off-by: Eric Biggers <ebiggers@...gle.com>
> > > ---
> > >  security/Kconfig.hardening | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening
> > > index 53baa95cb644..aad16187148c 100644
> > > --- a/security/Kconfig.hardening
> > > +++ b/security/Kconfig.hardening
> > > @@ -280,7 +280,8 @@ config ZERO_CALL_USED_REGS
> > >  endmenu
> > >
> > >  config CC_HAS_RANDSTRUCT
> > > -     def_bool $(cc-option,-frandomize-layout-seed-file=/dev/null)
> > > +     # Temporarily disabled due to https://github.com/llvm/llvm-project/issues/60349
> > > +     def_bool n
> > >
> > >  choice
> > >       prompt "Randomize layout of sensitive kernel structures"
> > >
> > > base-commit: 7b753a909f426f2789d9db6f357c3d59180a9354
> > > --
> > > 2.39.1
> >
> > This should be fixed with greater precision -- i.e. this is nearly fixed
> > in Clang now, and is likely to be backported. So I think we'll need
> > versioned checks here.
> >
> > --
> > Kees Cook
> >
>
> Bill has requested cherry-pick the llvm-project fix into the
> release/16.x branch [1].
> https://github.com/llvm/llvm-project-release-prs/pull/276
> It may take one day to land.
>
> [1]: https://github.com/llvm/llvm-project/tree/release/16.x
>
> --
> 宋方睿
>

All landed; the version check should be for 16+. (And the link to the
issue report would be nice to retain).
-- 
Thanks,
~Nick Desaulniers