Re: [patch 00/38] x86/retbleed: Call depth tracking mitigation

[Steven Rostedt]

On Wed, 20 Jul 2022 11:43:37 -0700
Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:

> So unless somebody has some one-liner workaround, I really suspect the
> fix is to remove all this. The amount of hackery to make it work in
> the first place is kind of disgusting anyway.
> 
> Since this was a WARN_ONCE(), can you make sure that with this case
> removed, nothing else triggers?

Actually, this fixes it too:

(and this config boots to completion without warnings).

I'll add this to my full test suite and see if it finishes.

-- Steve

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 1f40dad30d50..2dd61d8594f4 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -25,6 +25,7 @@ endif
 ifdef CONFIG_RETHUNK
 RETHUNK_CFLAGS		:= -mfunction-return=thunk-extern
 RETPOLINE_CFLAGS	+= $(RETHUNK_CFLAGS)
+export RETHUNK_CFLAGS
 endif
 
 export RETPOLINE_CFLAGS
diff --git a/drivers/misc/lkdtm/Makefile b/drivers/misc/lkdtm/Makefile
index 2e0aa74ac185..fd96ac1617f7 100644
--- a/drivers/misc/lkdtm/Makefile
+++ b/drivers/misc/lkdtm/Makefile
@@ -16,7 +16,7 @@ lkdtm-$(CONFIG_PPC_64S_HASH_MMU)	+= powerpc.o
 KASAN_SANITIZE_rodata.o		:= n
 KASAN_SANITIZE_stackleak.o	:= n
 KCOV_INSTRUMENT_rodata.o	:= n
-CFLAGS_REMOVE_rodata.o		+= $(CC_FLAGS_LTO)
+CFLAGS_REMOVE_rodata.o		+= $(CC_FLAGS_LTO) $(RETHUNK_CFLAGS)
 
 OBJCOPYFLAGS :=
 OBJCOPYFLAGS_rodata_objcopy.o	:= \