linux-kernel - [PATCH v2 0/2] link with -z noexecstack --no-warn-rwx-segments

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Message-Id: <20220810222442.2296651-3-ndesaulniers@google.com>
Date:   Wed, 10 Aug 2022 15:24:42 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     Fangrui Song <maskray@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Nick Clifton <nickc@...hat.com>, axboe@...nel.dk,
        brijesh.singh@....com, hpa@...or.com,
        kirill.shutemov@...ux.intel.com, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, michael.roth@....com, n.schier@....de,
        nathan@...nel.org, sathyanarayanan.kuppuswamy@...ux.intel.com,
        trix@...hat.com, x86@...nel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: [PATCH v2 0/2] link with -z noexecstack --no-warn-rwx-segments

Users of GNU ld (BFD) from binutils 2.39+ will observe multiple
instances of a new warning when linking kernels in the form:

  ld: warning: vmlinux: missing .note.GNU-stack
  section implies executable stack
  ld: NOTE: This behaviour is deprecated and will be removed in a future
  version of the linker
  ld: warning: vmlinux has a LOAD segment with RWX permissions

Generally, we would like to avoid the stack being executable. Because
there could be a need for the stack to be executable, assembler sources
have to opt-in to this security feature via explicit creation of the
.note.GNU-stack feature (which compilers create by default) or command
line flag --noexecstack. Or we can simply tell the linker the production
of such sections is irrelevant and to link the stack as --noexecstack.

LLVM's LLD linker defaults to -z noexecstack, so this flag isn't
strictly necessary when linking with LLD, only BFD, but it doesn't hurt
to be explicit here for all linkers IMO. --no-warn-rwx-segments is
currently BFD specific and only available in the current latest release,
so it's wrapped in an ld-option check.

While the kernel makes extensive usage of ELF sections, it doesn't use
permissions from ELF segments.

Broken up into 2 patches; one for the top level vmlinux, one x86
specific since a few places in the x86 build reset KBUILD_LDFLAGS.

Nick Desaulniers (2):
  Makefile: link with -z noexecstack --no-warn-rwx-segments
  x86: link vdso and boot with -z noexecstack --no-warn-rwx-segments

 Makefile                          | 5 +++++
 arch/x86/boot/Makefile            | 2 +-
 arch/x86/boot/compressed/Makefile | 4 ++++
 arch/x86/entry/vdso/Makefile      | 2 +-
 4 files changed, 11 insertions(+), 2 deletions(-)

base-commit: 15205c2829ca2cbb5ece5ceaafe1171a8470e62b
-- 
2.37.1.559.g78731f0fdb-goog