Currently, if the vDSO ends up containing an indirect branch or call, GCC will emit the "external thunk" style of retpoline, and it will fail to link.
Fix it by building the vDSO with inline retpoline thunks. I haven't seen any reports of this triggering on an unpatched kernel. Cc: Matt Rickard <[email protected]> Cc: Jason Vas Dias <[email protected]> Cc: David Woodhouse <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Andi Kleen <[email protected]> Fixes: commit 76b043848fd2 ("x86/retpoline: Add initial retpoline support") Signed-off-by: Andy Lutomirski <[email protected]> --- This is a bit of a marginal candidate for the merge window. There are a couple of reports of people hitting this while hacking on the vDSO, but I haven't seen any report of anyone hitting this on a stock kernel. Feel free to tell me to buzz of and send it later :) Makefile | 4 ++++ arch/x86/entry/vdso/Makefile | 6 ++++-- 2 files changed, 8 insertions(+), 2 deletions(-) diff --git a/Makefile b/Makefile index a0650bf79606..7bab2e90e4e1 100644 --- a/Makefile +++ b/Makefile @@ -507,9 +507,13 @@ KBUILD_AFLAGS += $(call cc-option, -no-integrated-as) endif RETPOLINE_CFLAGS_GCC := -mindirect-branch=thunk-extern -mindirect-branch-register +RETPOLINE_VDSO_CFLAGS_GCC := -mindirect-branch=thunk-inline -mindirect-branch-register RETPOLINE_CFLAGS_CLANG := -mretpoline-external-thunk +RETPOLINE_VDSO_CFLAGS_CLANG := -mretpoline RETPOLINE_CFLAGS := $(call cc-option,$(RETPOLINE_CFLAGS_GCC),$(call cc-option,$(RETPOLINE_CFLAGS_CLANG))) +RETPOLINE_VDSO_CFLAGS := $(call cc-option,$(RETPOLINE_VDSO_CFLAGS_GCC),$(call cc-option,$(RETPOLINE_VDSO_CFLAGS_CLANG))) export RETPOLINE_CFLAGS +export RETPOLINE_VDSO_CFLAGS KBUILD_CFLAGS += $(call cc-option,-fno-PIE) KBUILD_AFLAGS += $(call cc-option,-fno-PIE) diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile index 9f695f517747..fa3f439f0a92 100644 --- a/arch/x86/entry/vdso/Makefile +++ b/arch/x86/entry/vdso/Makefile @@ -68,9 +68,9 @@ $(obj)/vdso-image-%.c: $(obj)/vdso%.so.dbg $(obj)/vdso%.so $(obj)/vdso2c FORCE CFL := $(PROFILING) -mcmodel=small -fPIC -O2 -fasynchronous-unwind-tables -m64 \ $(filter -g%,$(KBUILD_CFLAGS)) $(call cc-option, -fno-stack-protector) \ -fno-omit-frame-pointer -foptimize-sibling-calls \ - -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO + -DDISABLE_BRANCH_PROFILING -DBUILD_VDSO $(RETPOLINE_VDSO_CFLAGS) -$(vobjs): KBUILD_CFLAGS := $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS)) $(CFL) +$(vobjs): KBUILD_CFLAGS := $(filter-out $(GCC_PLUGINS_CFLAGS) $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS)) $(CFL) # # vDSO code runs in userspace and -pg doesn't help with profiling anyway. @@ -132,11 +132,13 @@ KBUILD_CFLAGS_32 := $(filter-out -mcmodel=kernel,$(KBUILD_CFLAGS_32)) KBUILD_CFLAGS_32 := $(filter-out -fno-pic,$(KBUILD_CFLAGS_32)) KBUILD_CFLAGS_32 := $(filter-out -mfentry,$(KBUILD_CFLAGS_32)) KBUILD_CFLAGS_32 := $(filter-out $(GCC_PLUGINS_CFLAGS),$(KBUILD_CFLAGS_32)) +KBUILD_CFLAGS_32 := $(filter-out $(RETPOLINE_CFLAGS),$(KBUILD_CFLAGS_32)) KBUILD_CFLAGS_32 += -m32 -msoft-float -mregparm=0 -fpic KBUILD_CFLAGS_32 += $(call cc-option, -fno-stack-protector) KBUILD_CFLAGS_32 += $(call cc-option, -foptimize-sibling-calls) KBUILD_CFLAGS_32 += -fno-omit-frame-pointer KBUILD_CFLAGS_32 += -DDISABLE_BRANCH_PROFILING +KBUILD_CFLAGS_32 += $(RETPOLINE_VDSO_CFLAGS) $(obj)/vdso32.so.dbg: KBUILD_CFLAGS = $(KBUILD_CFLAGS_32) $(obj)/vdso32.so.dbg: FORCE \ -- 2.17.1
