From: Kees Cook <keescook@chromium.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
x86@kernel.org, Linus Torvalds <torvalds@linux-foundation.org>,
Tim Chen <tim.c.chen@linux.intel.com>,
Josh Poimboeuf <jpoimboe@kernel.org>,
Andrew Cooper <Andrew.Cooper3@citrix.com>,
Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
Johannes Wikner <kwikner@ethz.ch>,
Alyssa Milburn <alyssa.milburn@linux.intel.com>,
Jann Horn <jannh@google.com>, "H.J. Lu" <hjl.tools@gmail.com>,
Joao Moreira <joao.moreira@intel.com>,
Joseph Nuzman <joseph.nuzman@intel.com>,
Juergen Gross <jgross@suse.com>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>
Subject: Re: [PATCH] lkdtm: Keep the rodata test from causing retbleed WARNINGS
Date: Wed, 20 Jul 2022 13:13:05 -0700 [thread overview]
Message-ID: <202207201311.775CB068@keescook> (raw)
In-Reply-To: <20220720155507.4f904a58@gandalf.local.home>
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
next prev parent reply other threads:[~2022-07-20 20:13 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-20 19:55 [PATCH] lkdtm: Keep the rodata test from causing retbleed WARNINGS Steven Rostedt
2022-07-20 20:13 ` Kees Cook [this message]
2022-07-20 22:56 ` Josh Poimboeuf
2022-07-20 22:58 ` Josh Poimboeuf
2022-07-21 3:06 ` Kees Cook
2022-07-21 8:47 ` Peter Zijlstra
2022-07-21 13:51 ` Steven Rostedt
2022-07-21 15:58 ` Peter Zijlstra
2022-07-21 16:21 ` Steven Rostedt
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