linux-kernel - Re: [PATCH v8 00/21] Compile-time stack validation

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Message-ID: <55CBB9A1.7000800@canonical.com>
Date:	Wed, 12 Aug 2015 16:24:49 -0500
From:	Chris J Arges <chris.j.arges@...onical.com>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Michal Marek <mmarek@...e.cz>,
	Peter Zijlstra <peterz@...radead.org>,
	Andy Lutomirski <luto@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Pedro Alves <palves@...hat.com>,
	Namhyung Kim <namhyung@...il.com>,
	Bernd Petrovitsch <bernd@...rovitsch.priv.at>, x86@...nel.org,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 00/21] Compile-time stack validation

<snip>
> 
> Thanks for trying it out.  I couldn't figure out how to recreate this
> exact error, but I played around with "make mrproper" and saw some
> probably related errors.  Does this fix it?
> 
> ---8<---
> 
> Subject: [PATCH] stackvalidate: fix circular build dependencies
> 
> After "make mrproper" with CONFIG_STACK_VALIDATION enabled, I get the
> following errors:
> 
>   make[2]: *** No rule to make target 'arch/x86/purgatory/purgatory.o', needed by 'arch/x86/purgatory/purgatory.ro'.  Stop.
>   make[3]: *** No rule to make target 'scripts/mod/empty.o', needed by 'scripts/mod/elfconfig.h'.  Stop.
> 
> These are caused by circular dependencies.  The %.o pattern rules in
> scripts/Makefile.build have the stackvalidate binary listed as a
> dependency.  But stackvalidate gets built *after* archprepare and
> scripts/mod, both of which build objects using the %.o pattern rules.
> 
> The STACKVALIDATE and STACKVALIDATE_foo.o variables are already used to
> determine whether to validate a given object.  Also use them to
> determine whether to create the pattern rule dependency.
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> ---
>  scripts/Makefile.build | 7 +++++--
>  scripts/mod/Makefile   | 2 ++
>  2 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index a1270d3..ec96c51 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -243,7 +243,7 @@ endif
>  
>  ifdef CONFIG_STACK_VALIDATION
>  
> -stackvalidate = $(objtree)/scripts/stackvalidate/stackvalidate
> +__stackvalidate = $(objtree)/scripts/stackvalidate/stackvalidate
>  
>  ifndef CONFIG_FRAME_POINTER
>  nofp = --no-frame-pointer
> @@ -251,9 +251,12 @@ endif
>  
>  # Set STACKVALIDATE_foo.o=n to skip stack validation for a file.
>  # Set STACKVALIDATE=n to skip stack validation for a directory.
> +stackvalidate = $(if $(patsubst n%,, \
> +	$(STACKVALIDATE_$(basetarget).o)$(STACKVALIDATE)y), \
> +	$(__stackvalidate))
>  cmd_stackvalidate = $(if $(patsubst n%,, \
>  	$(STACKVALIDATE_$(basetarget).o)$(STACKVALIDATE)y), \
> -	$(stackvalidate) $(nofp) "$(@)";)
> +	$(__stackvalidate) $(nofp) "$(@)";)
>  
>  endif # CONFIG_STACK_VALIDATION
>  
> diff --git a/scripts/mod/Makefile b/scripts/mod/Makefile
> index c11212f..374c413 100644
> --- a/scripts/mod/Makefile
> +++ b/scripts/mod/Makefile
> @@ -1,3 +1,5 @@
> +STACKVALIDATE	:= n
> +
>  hostprogs-y	:= modpost mk_elfconfig
>  always		:= $(hostprogs-y) empty.o
>  
> 

Josh,

I still get build failures and I've pared it down to x86_64 defconfig plus:
CONFIG_MODVERSIONS=y
CONFIG_STACK_VALIDATION=y

And it seems like some modules may get the .tmp_foo.o treatment while
others end up foo.o so something like the following will not work:

cmd_stackvalidate = $(if $(patsubst n%,, \
        $(STACKVALIDATE_$(basetarget).o)$(STACKVALIDATE)y), \
        $(__stackvalidate) $(nofp) "$(@D)/.tmp_$(@F)";)

In addition, I'm not sure if skipping modules like STACKVALIDATE_foo.o=n
will still function properly for modversioned modules.

I'll try to look at this more tomorrow,
--chris j arges


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