lkdtm: Disable return thunks in rodata.c

The following warning was seen:

  WARNING: CPU: 0 PID: 0 at arch/x86/kernel/alternative.c:557 apply_returns (arch/x86/kernel/alternative.c:557 (discriminator 1))
  Modules linked in:
  CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.19.0-rc4-00008-gee88d363d156 #1
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.0-debian-1.16.0-4 04/01/2014
  RIP: 0010:apply_returns (arch/x86/kernel/alternative.c:557 (discriminator 1))
  Code: ff ff 74 cb 48 83 c5 04 49 39 ee 0f 87 81 fe ff ff e9 22 ff ff ff 0f 0b 48 83 c5 04 49 39 ee 0f 87 6d fe ff ff e9 0e ff ff ff <0f> 0b 48 83 c5 04 49 39 ee 0f 87 59 fe ff ff e9 fa fe ff ff 48 89

The warning happened when apply_returns() failed to convert "JMP
__x86_return_thunk" to RET.  It was instead a JMP to nowhere, due to the
thunk relocation not getting resolved.

That rodata.o code is objcopy'd to .rodata, and later memcpy'd, so
relocations don't work (and are apparently silently ignored).

LKDTM is only used for testing, so the naked RET should be fine.  So
just disable return thunks for that file.

While at it, disable objtool and KCSAN for the file.

Fixes: 84b05c840851 ("x86/retpoline: Use -mfunction-return")
Reported-by: kernel test robot <oliver.sang@intel.com>
Debugged-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/lkml/Ys58BxHxoDZ7rfpr@xsang-OptiPlex-9020/

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 1f40dad30d5084f50aaec155db49df961681cdd8..7854685c5f25b7926a6a722af83c134bd6ec6cd5 100644 (file)
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -27,6 +27,7 @@ RETHUNK_CFLAGS                := -mfunction-return=thunk-extern
 RETPOLINE_CFLAGS       += $(RETHUNK_CFLAGS)
 endif
 
+export RETHUNK_CFLAGS
 export RETPOLINE_CFLAGS
 export RETPOLINE_VDSO_CFLAGS
 

diff --git a/drivers/misc/lkdtm/Makefile b/drivers/misc/lkdtm/Makefile
index 2e0aa74ac18503becc7cac6fa6db59b853bd6802..95ef971b5e1cb4ce836fa0d2286ee2d81e28d8ce 100644 (file)
--- a/drivers/misc/lkdtm/Makefile
+++ b/drivers/misc/lkdtm/Makefile
@@ -13,10 +13,13 @@ lkdtm-$(CONFIG_LKDTM)               += cfi.o
 lkdtm-$(CONFIG_LKDTM)          += fortify.o
 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)
+
+KASAN_SANITIZE_rodata.o                        := n
+KCSAN_SANITIZE_rodata.o                        := n
+KCOV_INSTRUMENT_rodata.o               := n
+OBJECT_FILES_NON_STANDARD_rodata.o     := y
+CFLAGS_REMOVE_rodata.o                 += $(CC_FLAGS_LTO) $(RETHUNK_CFLAGS)
 
 OBJCOPYFLAGS :=
 OBJCOPYFLAGS_rodata_objcopy.o  := \