-fno-PIE, take #3

-fno-PIE, take #3

[Sebastian Andrzej Siewior]

Debian gcc's is nowdays compiled with --enable-default-pie which means it does
-fPIE by default. This breaks atleast x86-64 compiles.
This is the third attempt to fix it, this time by using runtime detection of
the -fno-PIE compiler switch (it was introduced in gcc 3.4, min required gcc is
currently 3.2) so it can be backported to the stable kernels.
As noted by Al this won't fix `git bisect' of stable kernels prio this commit.
However using always a wrapper around gcc which adds -fno-PIE is not sollution
I want to rely in future.

Sebastian

[PATCH 1/3] kbuild: add -fno-PIE

[Sebastian Andrzej Siewior]

Debian started to build the gcc with -fPIE by default so the kernel
build ends before it starts properly with:
|kernel/bounds.c:1:0: error: code model kernel does not support PIC mode

Also add to KBUILD_AFLAGS due to:

|gcc -Wp,-MD,arch/x86/entry/vdso/vdso32/.note.o.d … -mfentry -DCC_USING_FENTRY … vdso/vdso32/note.S
|arch/x86/entry/vdso/vdso32/note.S:1:0: sorry, unimplemented: -mfentry isn’t supported for 32-bit in combination with -fpic

Tagging it stable so it is possible to compile recent stable kernels as
well.

Cc: stable@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 Makefile | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Makefile b/Makefile
index a2650f9c6a25..d61145ebf498 100644
--- a/Makefile
+++ b/Makefile
@@ -622,6 +622,8 @@ include arch/$(SRCARCH)/Makefile
 KBUILD_CFLAGS	+= $(call cc-option,-fno-delete-null-pointer-checks,)
 KBUILD_CFLAGS	+= $(call cc-disable-warning,maybe-uninitialized,)
 KBUILD_CFLAGS	+= $(call cc-disable-warning,frame-address,)
+KBUILD_CFLAGS	+= $(call cc-option,-fno-PIE)
+KBUILD_AFLAGS	+= $(call cc-option,-fno-PIE)
 
 ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION
 KBUILD_CFLAGS	+= $(call cc-option,-ffunction-sections,)
-- 
2.10.2

[PATCH 2/3] scripts/has-stack-protector: add -fno-PIE

[Sebastian Andrzej Siewior]

Adding -no-PIE to the fstack protector check. -no-PIE was introduced
before -fstack-protector so there is no need for a runtime check.

Without it the build stops:
|Cannot use CONFIG_CC_STACKPROTECTOR_STRONG: -fstack-protector-strong available but compiler is broken

due to -mcmodel=kernel + -fPIE if -fPIE is enabled by default.

Tagging it stable so it is possible to compile recent stable kernels as
well.

Cc: stable@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 scripts/gcc-x86_64-has-stack-protector.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/gcc-x86_64-has-stack-protector.sh b/scripts/gcc-x86_64-has-stack-protector.sh
index 973e8c141567..17867e723a51 100755
--- a/scripts/gcc-x86_64-has-stack-protector.sh
+++ b/scripts/gcc-x86_64-has-stack-protector.sh
@@ -1,6 +1,6 @@
 #!/bin/sh
 
-echo "int foo(void) { char X[200]; return 3; }" | $* -S -x c -c -O0 -mcmodel=kernel -fstack-protector - -o - 2> /dev/null | grep -q "%gs"
+echo "int foo(void) { char X[200]; return 3; }" | $* -S -x c -c -O0 -mcmodel=kernel -fno-PIE -fstack-protector - -o - 2> /dev/null | grep -q "%gs"
 if [ "$?" -eq "0" ] ; then
 	echo y
 else
-- 
2.10.2

[PATCH 3/3] x86/kexec: add -fno-PIE

[Sebastian Andrzej Siewior]

If the gcc is configured to do -fPIE by default then the build aborts
later with:
| Unsupported relocation type: unknown type rel type name (29)

Tagging it stable so it is possible to compile recent stable kernels as
well.

Cc: stable@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 arch/x86/purgatory/Makefile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
index ac58c1616408..555b9fa0ad43 100644
--- a/arch/x86/purgatory/Makefile
+++ b/arch/x86/purgatory/Makefile
@@ -16,6 +16,7 @@ KCOV_INSTRUMENT := n
 
 KBUILD_CFLAGS := -fno-strict-aliasing -Wall -Wstrict-prototypes -fno-zero-initialized-in-bss -fno-builtin -ffreestanding -c -MD -Os -mcmodel=large
 KBUILD_CFLAGS += -m$(BITS)
+KBUILD_CFLAGS += $(call cc-option,-fno-PIE)
 
 $(obj)/purgatory.ro: $(PURGATORY_OBJS) FORCE
 		$(call if_changed,ld)
-- 
2.10.2

Re: -fno-PIE, take #3

[Theodore Ts'o]

On Fri, Nov 04, 2016 at 07:39:37PM +0100, Sebastian Andrzej Siewior wrote:
> Debian gcc's is nowdays compiled with --enable-default-pie which means it does
> -fPIE by default. This breaks atleast x86-64 compiles.
> This is the third attempt to fix it, this time by using runtime detection of
> the -fno-PIE compiler switch (it was introduced in gcc 3.4, min required gcc is
> currently 3.2) so it can be backported to the stable kernels.
> As noted by Al this won't fix `git bisect' of stable kernels prio this commit.
> However using always a wrapper around gcc which adds -fno-PIE is not sollution
> I want to rely in future.

A wrapper around gcc which adds -fno-PIE doesn't work for the HOSTCC
builds, anyway:

% gcc -fno-PIE -o /tmp/hello /tmp/hello.c
/usr/bin/ld: /tmp/cckzDf9X.o: relocation R_X86_64_32 against `.rodata' can not be used when making a shared object; recompile with -fPIC
/usr/bin/ld: final link failed: Nonrepresentable section on output
collect2: error: ld returned 1 exit status

Alas, the only workaround I've found which doesn't involve bisecting
the kernel is to add "CC=gcc-5" to the Makefile invocation (assuming
gcc-5 is installed of course).

					- Ted
					

Re: -fno-PIE, take #3

[H. Peter Anvin]

On 11/04/16 11:39, Sebastian Andrzej Siewior wrote:
> Debian gcc's is nowdays compiled with --enable-default-pie which means it does
> -fPIE by default. This breaks atleast x86-64 compiles.
> This is the third attempt to fix it, this time by using runtime detection of
> the -fno-PIE compiler switch (it was introduced in gcc 3.4, min required gcc is
> currently 3.2) so it can be backported to the stable kernels.
> As noted by Al this won't fix `git bisect' of stable kernels prio this commit.
> However using always a wrapper around gcc which adds -fno-PIE is not sollution
> I want to rely in future.
> 
> Sebastian
> 

We don't support gcc < 3.4 on x86 platforms; I'm pretty sure it is broken.

	-hpa

Re: -fno-PIE, take #3

[Borislav Petkov]

On Fri, Nov 04, 2016 at 07:39:37PM +0100, Sebastian Andrzej Siewior wrote:
> Debian gcc's is nowdays compiled with --enable-default-pie which means it does

Ho humm, there it is:

$ gcc -### /usr/include/stdlib.h 2>&1 | grep -o -- "--enable-default-pie"
--enable-default-pie

For all three:

Tested-by: Borislav Petkov <bp@suse.de>

That is, if that "fun" of building gcc with it doesn't get undone...

Thanks.

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

Re: [PATCH 1/3] kbuild: add -fno-PIE

[Michal Marek]

On Fri, Nov 04, 2016 at 07:39:38PM +0100, Sebastian Andrzej Siewior wrote:
> Debian started to build the gcc with -fPIE by default so the kernel
> build ends before it starts properly with:
> |kernel/bounds.c:1:0: error: code model kernel does not support PIC mode
> 
> Also add to KBUILD_AFLAGS due to:
> 
> |gcc -Wp,-MD,arch/x86/entry/vdso/vdso32/.note.o.d … -mfentry -DCC_USING_FENTRY … vdso/vdso32/note.S
> |arch/x86/entry/vdso/vdso32/note.S:1:0: sorry, unimplemented: -mfentry isn’t supported for 32-bit in combination with -fpic
> 
> Tagging it stable so it is possible to compile recent stable kernels as
> well.
> 
> Cc: stable@vger.kernel.org
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
>  Makefile | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/Makefile b/Makefile
> index a2650f9c6a25..d61145ebf498 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -622,6 +622,8 @@ include arch/$(SRCARCH)/Makefile
>  KBUILD_CFLAGS	+= $(call cc-option,-fno-delete-null-pointer-checks,)
>  KBUILD_CFLAGS	+= $(call cc-disable-warning,maybe-uninitialized,)
>  KBUILD_CFLAGS	+= $(call cc-disable-warning,frame-address,)
> +KBUILD_CFLAGS	+= $(call cc-option,-fno-PIE)
> +KBUILD_AFLAGS	+= $(call cc-option,-fno-PIE)

Bad compiler. No pie for you.

I applied this one to kbuild.git. How about 2/3 and 3/3. Will these be
merged via tip.git or shall I apply them as well?

Thanks,
Michal

Re: -fno-PIE, take #3

[Ben Hutchings]

[-- Attachment #1: Type: text/plain, Size: 1848 bytes --]

On Fri, 2016-11-04 at 19:39 +0100, Sebastian Andrzej Siewior wrote:
> Debian gcc's is nowdays compiled with --enable-default-pie which means it does
> -fPIE by default. This breaks atleast x86-64 compiles.
> This is the third attempt to fix it, this time by using runtime detection of
> the -fno-PIE compiler switch (it was introduced in gcc 3.4, min required gcc is
> currently 3.2) so it can be backported to the stable kernels.
> As noted by Al this won't fix `git bisect' of stable kernels prio this commit.
> However using always a wrapper around gcc which adds -fno-PIE is not sollution
> I want to rely in future.

I applied the previous version of "kbuild: add -fno-PIE" plus
"scripts/has-stack-protector: add -fno-PIE" to the Debian kernel
package of v4.9-rc3 and built with gcc-6, and the results of auto-
building so far are (from
<https://buildd.debian.org/status/package.php?p=linux&suite=experimental>):

Debian    Description                  Result
name
----------------------------------------------
amd64     x86_64                       OK
arm64     ARMv8                        OK
armel     ARMv5                        pending
armhf     ARMv7                        pending
i386      i686                         OK
mips      MIPS{32,64}r2 big-endian     OK
mipsel    MIPS{32,64}r2 little-endian  pending
mips64el  MIPS64r2, little-endian      pending
ppc64el   POWER8, little-endian        OK
s390x     s390x                        OK

PIE has not been enabled by default on other Debian architectures.  The
build failures on hppa and sparc64 are unrelated.

We do enable CONFIG_KEXEC_FILE on amd64 so I don't know how why that
build succeeded without "x86/kexec: add -fno-PIE".

Ben.

-- 
Ben Hutchings
For every complex problem
there is a solution that is simple, neat, and wrong.

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Re: [PATCH 1/3] kbuild: add -fno-PIE

[Ingo Molnar]

* Michal Marek <mmarek@suse.com> wrote:

> On Fri, Nov 04, 2016 at 07:39:38PM +0100, Sebastian Andrzej Siewior wrote:
> > Debian started to build the gcc with -fPIE by default so the kernel
> > build ends before it starts properly with:
> > |kernel/bounds.c:1:0: error: code model kernel does not support PIC mode
> > 
> > Also add to KBUILD_AFLAGS due to:
> > 
> > |gcc -Wp,-MD,arch/x86/entry/vdso/vdso32/.note.o.d … -mfentry -DCC_USING_FENTRY … vdso/vdso32/note.S
> > |arch/x86/entry/vdso/vdso32/note.S:1:0: sorry, unimplemented: -mfentry isn’t supported for 32-bit in combination with -fpic
> > 
> > Tagging it stable so it is possible to compile recent stable kernels as
> > well.
> > 
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> > ---
> >  Makefile | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/Makefile b/Makefile
> > index a2650f9c6a25..d61145ebf498 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -622,6 +622,8 @@ include arch/$(SRCARCH)/Makefile
> >  KBUILD_CFLAGS	+= $(call cc-option,-fno-delete-null-pointer-checks,)
> >  KBUILD_CFLAGS	+= $(call cc-disable-warning,maybe-uninitialized,)
> >  KBUILD_CFLAGS	+= $(call cc-disable-warning,frame-address,)
> > +KBUILD_CFLAGS	+= $(call cc-option,-fno-PIE)
> > +KBUILD_AFLAGS	+= $(call cc-option,-fno-PIE)
> 
> Bad compiler. No pie for you.
> 
> I applied this one to kbuild.git. How about 2/3 and 3/3. Will these be
> merged via tip.git or shall I apply them as well?

I'd suggest applying them to the kbuild tree, as they are related.

Thanks,

	Ingo

Re: [PATCH 1/3] kbuild: add -fno-PIE

[Michal Marek]

Dne 9.11.2016 v 07:10 Ingo Molnar napsal(a):
> 
> * Michal Marek <mmarek@suse.com> wrote:
> 
>> On Fri, Nov 04, 2016 at 07:39:38PM +0100, Sebastian Andrzej Siewior wrote:
>>> Debian started to build the gcc with -fPIE by default so the kernel
>>> build ends before it starts properly with:
>>> |kernel/bounds.c:1:0: error: code model kernel does not support PIC mode
>>>
>>> Also add to KBUILD_AFLAGS due to:
>>>
>>> |gcc -Wp,-MD,arch/x86/entry/vdso/vdso32/.note.o.d … -mfentry -DCC_USING_FENTRY … vdso/vdso32/note.S
>>> |arch/x86/entry/vdso/vdso32/note.S:1:0: sorry, unimplemented: -mfentry isn’t supported for 32-bit in combination with -fpic
>>>
>>> Tagging it stable so it is possible to compile recent stable kernels as
>>> well.
>>>
>>> Cc: stable@vger.kernel.org
>>> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
>>> ---
>>>  Makefile | 2 ++
>>>  1 file changed, 2 insertions(+)
>>>
>>> diff --git a/Makefile b/Makefile
>>> index a2650f9c6a25..d61145ebf498 100644
>>> --- a/Makefile
>>> +++ b/Makefile
>>> @@ -622,6 +622,8 @@ include arch/$(SRCARCH)/Makefile
>>>  KBUILD_CFLAGS	+= $(call cc-option,-fno-delete-null-pointer-checks,)
>>>  KBUILD_CFLAGS	+= $(call cc-disable-warning,maybe-uninitialized,)
>>>  KBUILD_CFLAGS	+= $(call cc-disable-warning,frame-address,)
>>> +KBUILD_CFLAGS	+= $(call cc-option,-fno-PIE)
>>> +KBUILD_AFLAGS	+= $(call cc-option,-fno-PIE)
>>
>> Bad compiler. No pie for you.
>>
>> I applied this one to kbuild.git. How about 2/3 and 3/3. Will these be
>> merged via tip.git or shall I apply them as well?
> 
> I'd suggest applying them to the kbuild tree, as they are related.

OK, done.

Michal

Re: [PATCH 1/3] kbuild: add -fno-PIE

[Ingo Molnar]

* Michal Marek <mmarek@suse.com> wrote:

> >>> +++ b/Makefile
> >>> @@ -622,6 +622,8 @@ include arch/$(SRCARCH)/Makefile
> >>>  KBUILD_CFLAGS	+= $(call cc-option,-fno-delete-null-pointer-checks,)
> >>>  KBUILD_CFLAGS	+= $(call cc-disable-warning,maybe-uninitialized,)
> >>>  KBUILD_CFLAGS	+= $(call cc-disable-warning,frame-address,)
> >>> +KBUILD_CFLAGS	+= $(call cc-option,-fno-PIE)
> >>> +KBUILD_AFLAGS	+= $(call cc-option,-fno-PIE)
> >>
> >> Bad compiler. No pie for you.
> >>
> >> I applied this one to kbuild.git. How about 2/3 and 3/3. Will these be
> >> merged via tip.git or shall I apply them as well?
> > 
> > I'd suggest applying them to the kbuild tree, as they are related.
> 
> OK, done.

Thanks!

	Ingo