From: Kees Cook <keescook@chromium.org>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Will Deacon <will@kernel.org>, Dave Martin <Dave.Martin@arm.com>,
clang-built-linux <clang-built-linux@googlegroups.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Mark Rutland <mark.rutland@arm.com>,
Peter Collingbourne <pcc@google.com>,
James Morse <james.morse@arm.com>, Borislav Petkov <bp@suse.de>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
Russell King <linux@armlinux.org.uk>,
Masahiro Yamada <masahiroy@kernel.org>,
Arvind Sankar <nivedita@alum.mit.edu>,
Nick Desaulniers <ndesaulniers@google.com>,
Nathan Chancellor <natechancellor@gmail.com>,
Arnd Bergmann <arnd@arndb.de>, X86 ML <x86@kernel.org>,
linux-arch <linux-arch@vger.kernel.org>,
linux-efi <linux-efi@vger.kernel.org>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 05/17] ctype: Work around Clang -mbranch-protection=none bug
Date: Mon, 29 Jun 2020 07:43:36 -0700 [thread overview]
Message-ID: <202006290742.92EC7235@keescook> (raw)
In-Reply-To: <CAMj1kXE+toCd=Bx-zw7D9bvDRNB2aPn5-_7CY7MOKcVGA-azVg@mail.gmail.com>
On Mon, Jun 29, 2020 at 10:15:47AM +0200, Ard Biesheuvel wrote:
> On Mon, 29 Jun 2020 at 08:18, Kees Cook <keescook@chromium.org> wrote:
> >
> > In preparation for building efi/libstub with -mbranch-protection=none
> > (EFI does not support branch protection features[1]), add no-op code
> > to work around a Clang bug that emits an unwanted .note.gnu.property
> > section for object files without code[2].
> >
> > [1] https://lore.kernel.org/lkml/CAMj1kXHck12juGi=E=P4hWP_8vQhQ+-x3vBMc3TGeRWdQ-XkxQ@mail.gmail.com
> > [2] https://bugs.llvm.org/show_bug.cgi?id=46480
> >
> > Cc: Ard Biesheuvel <ardb@kernel.org>
> > Cc: Will Deacon <will@kernel.org>
> > Cc: Dave Martin <Dave.Martin@arm.com>
> > Cc: clang-built-linux@googlegroups.com
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> > ---
> > lib/ctype.c | 10 ++++++++++
> > 1 file changed, 10 insertions(+)
> >
> > diff --git a/lib/ctype.c b/lib/ctype.c
> > index c819fe269eb2..21245ed57d90 100644
> > --- a/lib/ctype.c
> > +++ b/lib/ctype.c
> > @@ -36,3 +36,13 @@ _L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L,_L, /* 224-239 */
> > _L,_L,_L,_L,_L,_L,_L,_P,_L,_L,_L,_L,_L,_L,_L,_L}; /* 240-255 */
> >
> > EXPORT_SYMBOL(_ctype);
> > +
> > +/*
> > + * Clang will generate .note.gnu.property sections for object files
> > + * without code, even in the presence of -mbranch-protection=none.
> > + * To work around this, define an unused static function.
> > + * https://bugs.llvm.org/show_bug.cgi?id=46480
> > + */
> > +#ifdef CONFIG_CC_IS_CLANG
> > +void __maybe_unused __clang_needs_code_here(void) { }
> > +#endif
> > --
> > 2.25.1
> >
>
> I take it we don't need this horrible hack if we build the EFI stub
> with branch protections and filter out the .note.gnu.property section
> explicitly?
Correct.
> Sorry to backpedal, but that is probably a better approach after all,
> given that the instructions don't hurt, and we will hopefully be able
> to arm them once UEFI (as well as PE/COFF) gets around to describing
> this in a way that both the firmware and the OS can consume.
Okay, will revert to the v3 solution.
--
Kees Cook
next prev parent reply other threads:[~2020-06-29 19:32 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-29 6:18 [PATCH v4 00/17] Warn on orphan section placement Kees Cook
2020-06-29 6:18 ` [PATCH v4 01/17] vmlinux.lds.h: Add .gnu.version* to DISCARDS Kees Cook
2020-06-29 6:18 ` [PATCH v4 02/17] vmlinux.lds.h: Avoid KASAN and KCSAN's unwanted sections Kees Cook
2020-06-29 6:18 ` [PATCH v4 03/17] vmlinux.lds.h: Split ELF_DETAILS from STABS_DEBUG Kees Cook
2020-06-29 6:18 ` [PATCH v4 04/17] vmlinux.lds.h: Add .symtab, .strtab, and .shstrtab to ELF_DETAILS Kees Cook
2020-06-29 6:18 ` [PATCH v4 05/17] ctype: Work around Clang -mbranch-protection=none bug Kees Cook
2020-06-29 8:15 ` Ard Biesheuvel
2020-06-29 14:43 ` Kees Cook [this message]
2020-06-29 15:06 ` Kees Cook
2020-06-29 15:08 ` Ard Biesheuvel
2020-06-29 15:16 ` Kees Cook
2020-06-29 18:02 ` Nick Desaulniers
2020-06-29 18:37 ` Kees Cook
2020-06-29 6:18 ` [PATCH v4 06/17] efi/libstub: Disable -mbranch-protection Kees Cook
2020-06-29 6:18 ` [PATCH v4 07/17] arm64/build: Use common DISCARDS in linker script Kees Cook
2020-06-29 6:18 ` [PATCH v4 08/17] arm64/mm: Remove needless section quotes Kees Cook
2020-06-29 19:53 ` Nick Desaulniers
2020-06-29 20:03 ` Joe Perches
2020-06-29 20:29 ` Nick Desaulniers
2020-06-29 20:04 ` Kees Cook
2020-06-29 20:54 ` Arvind Sankar
2020-06-29 21:06 ` Arvind Sankar
2020-06-29 6:18 ` [PATCH v4 09/17] arm64/build: Remove .eh_frame* sections due to unwind tables Kees Cook
2020-06-29 6:18 ` [PATCH v4 10/17] arm64/kernel: Remove needless Call Frame Information annotations Kees Cook
2020-06-29 6:18 ` [PATCH v4 11/17] arm64/build: Warn on orphan section placement Kees Cook
2020-06-29 6:18 ` [PATCH v4 12/17] arm/build: Refactor linker script headers Kees Cook
2020-06-29 6:18 ` [PATCH v4 13/17] arm/build: Explicitly keep .ARM.attributes sections Kees Cook
2020-06-29 6:18 ` [PATCH v4 14/17] arm/build: Warn on orphan section placement Kees Cook
2020-06-29 15:54 ` Arvind Sankar
2020-06-29 18:07 ` Russell King - ARM Linux admin
2020-06-29 18:15 ` Arvind Sankar
2020-06-29 19:03 ` Russell King - ARM Linux admin
2020-06-29 19:47 ` Nick Desaulniers
2020-06-29 6:18 ` [PATCH v4 15/17] arm/boot: " Kees Cook
2020-06-29 6:18 ` [PATCH v4 16/17] x86/build: " Kees Cook
2020-06-29 6:18 ` [PATCH v4 17/17] x86/boot: " Kees Cook
2020-08-21 16:02 ` [PATCH v4 00/17] " Will Deacon
2020-08-21 17:36 ` Kees Cook
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