Messages in this thread | | | Date | Wed, 20 Jul 2022 13:13:05 -0700 | From | Kees Cook <> | Subject | Re: [PATCH] lkdtm: Keep the rodata test from causing retbleed WARNINGS |
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On Wed, Jul 20, 2022 at 03:55:07PM -0400, Steven Rostedt wrote: > From: "Steven Rostedt (Google)" <rostedt@goodmis.org> > > The rodata test checks if executable code in the .rodata section will not > execute. But this also means that fix ups that the return hook code does > will not be able to change this code at boot up, and this causes a > warning. > > By removing the RETHOOK_CFLAGS from the compilation of the rodata function > makes it hidden from objtool and it will not add its return hook into the > .returns section. This keeps the fix up code from trying and failing on > modifying the rodata return call. > > Link: https://lore.kernel.org/all/20220720125736.48164a14@gandalf.local.home/ > > Fixes: ee88d363d1561 ("x86,static_call: Use alternative RET encoding") > Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Yeah, this matches a portion of what was suggested: https://lore.kernel.org/lkml/20220713213133.455599-1-keescook@chromium.org/
But it still needed objtool fixes: https://lore.kernel.org/lkml/20220715032333.neywlazczbb35w3b@treble/
Perhaps objtool has already had patches landed for this? (Otherwise the patch you suggested would fail to build on x86 with rethunk support.)
-Kees
> --- > > [ Note, my tests are still running with this, but it passed the test that > caused the failure, so I decided to post this now. ] > > arch/x86/Makefile | 1 + > drivers/misc/lkdtm/Makefile | 2 +- > 2 files changed, 2 insertions(+), 1 deletion(-) > > 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 := \ > -- > 2.35.1 >
-- Kees Cook
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