[PATCH RFC 23/43] x86/pie: Force hidden visibility for all symbol references

[Hou Wenlong]

Eliminate all GOT entries in the kernel, by forcing hidden visibility
for all symbol references, which informs the compiler that such
references will be resolved at link time without the need for allocating
GOT entries. However, there are still some GOT entries after this, one
for __fentry__() indirect call, and others are due to global weak symbol
references.

Signed-off-by: Hou Wenlong <houwenlong.hwl@xxxxxxxxxxxx>
Cc: Thomas Garnier <thgarnie@xxxxxxxxxxxx>
Cc: Lai Jiangshan <jiangshan.ljs@xxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
---
 arch/x86/Makefile            | 7 +++++++
 arch/x86/entry/vdso/Makefile | 2 +-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 57e4dbbf501d..81500011396d 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -158,6 +158,11 @@ else
         KBUILD_RUSTFLAGS += $(rustflags-y)
 
         KBUILD_CFLAGS += -mno-red-zone
+
+ifdef CONFIG_X86_PIE
+        PIE_CFLAGS := -include $(srctree)/include/linux/hidden.h
+        KBUILD_CFLAGS += $(PIE_CFLAGS)
+endif
         KBUILD_CFLAGS += -mcmodel=kernel
         KBUILD_RUSTFLAGS += -Cno-redzone=y
         KBUILD_RUSTFLAGS += -Ccode-model=kernel
@@ -176,6 +181,8 @@ ifeq ($(CONFIG_STACKPROTECTOR),y)
 	endif
 endif
 
+export PIE_CFLAGS
+
 #
 # If the function graph tracer is used with mcount instead of fentry,
 # '-maccumulate-outgoing-args' is needed to prevent a GCC bug
diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
index 6a1821bd7d5e..9437653a9de2 100644
--- a/arch/x86/entry/vdso/Makefile
+++ b/arch/x86/entry/vdso/Makefile
@@ -92,7 +92,7 @@ ifneq ($(RETPOLINE_VDSO_CFLAGS),)
 endif
 endif
 
-$(vobjs): KBUILD_CFLAGS := $(filter-out $(PADDING_CFLAGS) $(CC_FLAGS_LTO) $(CC_FLAGS_CFI) $(RANDSTRUCT_CFLAGS) $(GCC_PLUGINS_CFLAGS) $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS)) $(CFL)
+$(vobjs): KBUILD_CFLAGS := $(filter-out $(PIE_CFLAGS) $(PADDING_CFLAGS) $(CC_FLAGS_LTO) $(CC_FLAGS_CFI) $(RANDSTRUCT_CFLAGS) $(GCC_PLUGINS_CFLAGS) $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS)) $(CFL)
 $(vobjs): KBUILD_AFLAGS += -DBUILD_VDSO
 
 #
-- 
2.31.1