Date: Wed, 4 Oct 2017 17:13:12 +0200 From: Greg KH <greg@...ah.com> To: Masahiro Yamada <yamada.masahiro@...ionext.com> Cc: Kees Cook <keescook@...omium.org>, Andrew Morton <akpm@...ux-foundation.org>, Michal Marek <mmarek@...e.com>, Ingo Molnar <mingo@...nel.org>, Laura Abbott <labbott@...hat.com>, Nicholas Piggin <npiggin@...il.com>, Al Viro <viro@...iv.linux.org.uk>, Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>, Yoshinori Sato <ysato@...rs.sourceforge.jp>, Rich Felker <dalias@...c.org>, "David S. Miller" <davem@...emloft.net>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, linux-sh@...r.kernel.org, kernel-hardening@...ts.openwall.com, Mark Rutland <mark.rutland@....com> Subject: Re: Re: [PATCH 2/3] Makefile: Move stackprotector availability out of Kconfig On Wed, Oct 04, 2017 at 11:33:38PM +0900, Masahiro Yamada wrote: > Hi Kees, > > > 2017-10-03 4:20 GMT+09:00 Kees Cook <keescook@...omium.org>: > > Various portions of the kernel, especially per-architecture pieces, > > need to know if the compiler is building it with the stack protector. > > This was done in the arch/Kconfig with 'select', but this doesn't > > allow a way to do auto-detected compiler support. In preparation for > > creating an on-if-available default, move the logic for the definition of > > CONFIG_CC_STACKPROTECTOR into the Makefile. > > > > Cc: Masahiro Yamada <yamada.masahiro@...ionext.com> > > Cc: Michal Marek <mmarek@...e.com> > > Cc: Andrew Morton <akpm@...ux-foundation.org> > > Cc: Ingo Molnar <mingo@...nel.org> > > Cc: Laura Abbott <labbott@...hat.com> > > Cc: Nicholas Piggin <npiggin@...il.com> > > Cc: Al Viro <viro@...iv.linux.org.uk> > > Cc: linux-kbuild@...r.kernel.org > > Signed-off-by: Kees Cook <keescook@...omium.org> > > --- > > Makefile | 7 +++++-- > > arch/Kconfig | 8 -------- > > 2 files changed, 5 insertions(+), 10 deletions(-) > > > > diff --git a/Makefile b/Makefile > > index d1119941261c..e122a9cf0399 100644 > > --- a/Makefile > > +++ b/Makefile > > @@ -688,8 +688,11 @@ else > > stackp-flag := $(call cc-option, -fno-stack-protector) > > endif > > endif > > -# Find arch-specific stack protector compiler sanity-checking script. > > -ifdef CONFIG_CC_STACKPROTECTOR > > +ifdef stackp-name > > + # If the stack protector has been selected, inform the rest of the build. > > + KBUILD_CFLAGS += -DCONFIG_CC_STACKPROTECTOR > > + KBUILD_AFLAGS += -DCONFIG_CC_STACKPROTECTOR > > + # Find arch-specific stack protector compiler sanity-checking script. > > stackp-path := $(srctree)/scripts/gcc-$(SRCARCH)_$(BITS)-has-stack-protector.sh > > stackp-check := $(wildcard $(stackp-path)) > > endif > > > I have not tested this series, > but I think this commit is bad (with the follow-up patch applied). > > > I thought of this scenario: > >  Kernel is configured with CONFIG_CC_STACKPROTECTOR_AUTO > >  Kernel is built with a compiler without stack protector support. > >  CONFIG_CC_STACKPROTECTOR is not defined, > so __stack_chk_fail() is not compiled. > >  Out-of-tree modules are compiled with a compiler with > stack protector support. > __stack_chk_fail() is inserted to functions of the modules. We don't ever support the system of loading a module built with anything other than the _exact_ same compiler than the kernel was. So this will not happen (well, if someone tries it, they get to keep the pieces their kernel image is now in...) >  insmod fails because reference to __stack_chk_fail() > can not be resolved. Even nicer, we failed "cleanly" :) This isn't a real-world issue, sorry. thanks, greg k-h
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