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Date:   Wed, 10 Aug 2022 15:24:40 -0700
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Subject: [PATCH v2 1/2] Makefile: link with -z noexecstack --no-warn-rwx-segments
From:   Nick Desaulniers <ndesaulniers@google.com>
To:     Masahiro Yamada <masahiroy@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>
Cc:     Fangrui Song <maskray@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Nick Clifton <nickc@redhat.com>, axboe@kernel.dk,
        brijesh.singh@amd.com, hpa@zytor.com,
        kirill.shutemov@linux.intel.com, linux-kernel@vger.kernel.org,
        llvm@lists.linux.dev, michael.roth@amd.com, n.schier@avm.de,
        nathan@kernel.org, sathyanarayanan.kuppuswamy@linux.intel.com,
        trix@redhat.com, x86@kernel.org,
        Nick Desaulniers <ndesaulniers@google.com>,
        Michal Marek <michal.lkml@markovi.net>,
        linux-kbuild@vger.kernel.org
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Precedence: bulk

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.

Link: https://lore.kernel.org/linux-block/3af4127a-f453-4cf7-f133-a181cce06f73@kernel.dk/
Link: https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=ba951afb99912da01a6e8434126b8fac7aa75107
Link: https://github.com/llvm/llvm-project/issues/57009
Reported-by: Jens Axboe <axboe@kernel.dk>
Suggested-by: Fangrui Song <maskray@google.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
 Makefile | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/Makefile b/Makefile
index dc6295f91263..230e6e7679f9 100644
--- a/Makefile
+++ b/Makefile
@@ -1033,6 +1033,11 @@ KBUILD_CFLAGS   += $(KCFLAGS)
 KBUILD_LDFLAGS_MODULE += --build-id=sha1
 LDFLAGS_vmlinux += --build-id=sha1
 
+KBUILD_LDFLAGS	+= -z noexecstack
+ifeq ($(CONFIG_LD_IS_BFD),y)
+KBUILD_LDFLAGS	+= $(call ld-option,--no-warn-rwx-segments)
+endif
+
 ifeq ($(CONFIG_STRIP_ASM_SYMS),y)
 LDFLAGS_vmlinux	+= $(call ld-option, -X,)
 endif
-- 
2.37.1.559.g78731f0fdb-goog