Michael Ellerman [off-list ref] writes:

Christophe LEROY [off-list ref] writes:

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Le 24/09/2018 =C3=A0 14:10, Michael Ellerman a =C3=A9crit=C2=A0:

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Christophe Leroy [off-list ref] writes:

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I'm trying to implement TLS based stack protector in the Linux Kernel.
For that I need to give to GCC the offset at which it will find the
canary (register r2 is pointing to the current task struct).

I have been able to do it with the below patch, but it only works when
include/generated/asm-offsets.h already exists from the start of the b=

uild.

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Is there a way to evaluate CANARY_OFFSET and add the stack-protector
flags to KBUILD_FLAGS only after include/generated/asm-offsets.h is bu=

ilt ?

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Or another way of add -mstack-protector-guard-offset=3Doffsetof(struct
task_struct, stack_canary) ?

=20
This seems to work, at least I see the value in CFLAGS:
=20

diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index 07d9dce..39ee113 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile

@@ -404,6 +394,11 @@ archclean:

=20=20=20
  archprepare: checkbin
=20=20=20
+prepare: stack_protector_prepare
+
+stack_protector_prepare: prepare0
+	$(eval KBUILD_CFLAGS +=3D -mstack-protector-guard-offset=3D$(shell aw=

k '{if ($$2 =3D=3D "TSK_STACK_CANARY") print $$3;}' include/generated/asm-o=
ffsets.h))

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+

Great, it works !
Thanks, I have sent v3 of the patches.

Cool.

It would be good to here from someone who knows Kbuild better than me if

                      ^
                      hear

Still learning English.

cheers