The following commit has been merged into the core/build branch of tip:

Commit-ID:     e2179a09ab089d3423751bd2b0c884ddb3eabe84
Gitweb:        
https://git.kernel.org/tip/e2179a09ab089d3423751bd2b0c884ddb3eabe84
Author:        Kees Cook <keesc...@chromium.org>
AuthorDate:    Fri, 21 Aug 2020 12:42:48 -07:00
Committer:     Ingo Molnar <mi...@kernel.org>
CommitterDate: Tue, 01 Sep 2020 09:50:36 +02:00

efi/libstub: Disable -mbranch-protection

In preparation for adding --orphan-handling=warn to more architectures,
disable -mbranch-protection, as EFI does not yet support it[1].  This was
noticed due to it producing unwanted .note.gnu.property sections (prefixed
with .init due to the objcopy build step).

However, we must also work around a bug in Clang where the section is
still emitted for code-less object files[2], so also remove the section
during the objcopy.

[1] 
https://lore.kernel.org/lkml/CAMj1kXHck12juGi=E=p4hwp_8vqhq+-x3vbmc3tgerwdq-x...@mail.gmail.com
[2] https://bugs.llvm.org/show_bug.cgi?id=46480

Signed-off-by: Kees Cook <keesc...@chromium.org>
Signed-off-by: Ingo Molnar <mi...@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulni...@google.com>
Acked-by: Ard Biesheuvel <a...@kernel.org>
Link: https://lore.kernel.org/r/20200821194310.3089815-8-keesc...@chromium.org
---
 drivers/firmware/efi/libstub/Makefile |  9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/libstub/Makefile 
b/drivers/firmware/efi/libstub/Makefile
index 5eefd60..0c911e3 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -18,7 +18,8 @@ cflags-$(CONFIG_X86)          += -m$(BITS) -D__KERNEL__ \
 # arm64 uses the full KBUILD_CFLAGS so it's necessary to explicitly
 # disable the stackleak plugin
 cflags-$(CONFIG_ARM64)         := $(subst 
$(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
-                                  -fpie $(DISABLE_STACKLEAK_PLUGIN)
+                                  -fpie $(DISABLE_STACKLEAK_PLUGIN) \
+                                  $(call cc-option,-mbranch-protection=none)
 cflags-$(CONFIG_ARM)           := $(subst 
$(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
                                   -fno-builtin -fpic \
                                   $(call cc-option,-mno-single-pic-base)
@@ -66,6 +67,12 @@ lib-$(CONFIG_X86)            += x86-stub.o
 CFLAGS_arm32-stub.o            := -DTEXT_OFFSET=$(TEXT_OFFSET)
 CFLAGS_arm64-stub.o            := -DTEXT_OFFSET=$(TEXT_OFFSET)
 
+# Even when -mbranch-protection=none is set, Clang will generate a
+# .note.gnu.property for code-less object files (like lib/ctype.c),
+# so work around this by explicitly removing the unwanted section.
+# https://bugs.llvm.org/show_bug.cgi?id=46480
+STUBCOPY_FLAGS-y               += --remove-section=.note.gnu.property
+
 #
 # For x86, bootloaders like systemd-boot or grub-efi do not zero-initialize the
 # .bss section, so the .bss section of the EFI stub needs to be included in the

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