From efc72a665a61fd48c462f5248a9e3dc991398ddd Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Mon, 18 Jul 2022 07:50:25 -0700 Subject: [PATCH] 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: 0b53c374b9ef ("x86/retpoline: Use -mfunction-return") Reported-by: kernel test robot Debugged-by: Peter Zijlstra Signed-off-by: Josh Poimboeuf Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/lkml/Ys58BxHxoDZ7rfpr@xsang-OptiPlex-9020/ --- arch/x86/Makefile | 1 + drivers/misc/lkdtm/Makefile | 9 ++++++--- 2 files changed, 7 insertions(+), 3 deletions(-) diff --git a/arch/x86/Makefile b/arch/x86/Makefile index 1f40dad30d50..7854685c5f25 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -27,6 +27,7 @@ RETHUNK_CFLAGS := -mfunction-return=thunk-extern RETPOLINE_CFLAGS += $(RETHUNK_CFLAGS) endif +export RETHUNK_CFLAGS export RETPOLINE_CFLAGS export RETPOLINE_VDSO_CFLAGS diff --git a/drivers/misc/lkdtm/Makefile b/drivers/misc/lkdtm/Makefile index 2e0aa74ac185..95ef971b5e1c 100644 --- a/drivers/misc/lkdtm/Makefile +++ b/drivers/misc/lkdtm/Makefile @@ -13,10 +13,13 @@ lkdtm-$(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 := \ -- 2.20.1