Recent versions of GCC will emit literals into a separate .rodata section
rather than interspersed with the instruction stream. We disabled this
in commit 67dfa1751ce71 ("arm64: errata: Add -mpc-relative-literal-loads
to build flags"), because it uses adrp/add pairs to reference these
literals even when building with -mcmodel=large, which breaks module
loading when we have the mitigation for Cortex-A53 erratum #843419
enabled.
However, due to the recent discoveries regarding speculative execution,
we should avoid putting data into executable sections, to prevent
creating speculative gadgets inadvertently.
So set -mpc-relative-literal-loads only for modules, and only if the
A53 erratum is enabled.
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
---
arch/arm64/Makefile | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index b481b4a7c011..bd7cb205e28a 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -26,7 +26,8 @@ ifeq ($(CONFIG_ARM64_ERRATUM_843419),y)
ifeq ($(call ld-option, --fix-cortex-a53-843419),)
$(warning ld does not support --fix-cortex-a53-843419; kernel may be susceptible to erratum)
else
-LDFLAGS_vmlinux += --fix-cortex-a53-843419
+LDFLAGS_vmlinux += --fix-cortex-a53-843419
+KBUILD_CFLAGS_MODULE += $(call cc-option, -mpc-relative-literal-loads)
endif
endif
@@ -51,7 +52,6 @@ endif
KBUILD_CFLAGS += -mgeneral-regs-only $(lseinstr) $(brokengasinst)
KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
-KBUILD_CFLAGS += $(call cc-option, -mpc-relative-literal-loads)
KBUILD_AFLAGS += $(lseinstr) $(brokengasinst)
KBUILD_CFLAGS += $(call cc-option,-mabi=lp64)
--
2.11.0
