Re: [PATCH v3 2/2] powerpc/64: add stack protector support

From: Christophe LEROY
Date: Tue Sep 25 2018 - 11:56:16 EST

Snowpatch reports failure on pmac32_defconfig, as follows:

arch/powerpc/platforms/powermac/bootx_init.o: In function `bootx_printf':
/var/lib/jenkins-slave/workspace/snowpatch/snowpatch-linux-sparse/linux/arch/powerpc/platforms/powermac/bootx_init.c:88: undefined reference to `__stack_chk_fail_local'
arch/powerpc/platforms/powermac/bootx_init.o: In function `bootx_add_display_props':
/var/lib/jenkins-slave/workspace/snowpatch/snowpatch-linux-sparse/linux/arch/powerpc/platforms/powermac/bootx_init.c:211: undefined reference to `__stack_chk_fail_local'
arch/powerpc/platforms/powermac/bootx_init.o: In function `bootx_scan_dt_build_struct':
/var/lib/jenkins-slave/workspace/snowpatch/snowpatch-linux-sparse/linux/arch/powerpc/platforms/powermac/bootx_init.c:350: undefined reference to `__stack_chk_fail_local'
arch/powerpc/platforms/powermac/bootx_init.o: In function `bootx_init':
/var/lib/jenkins-slave/workspace/snowpatch/snowpatch-linux-sparse/linux/arch/powerpc/platforms/powermac/bootx_init.c:598: undefined reference to `__stack_chk_fail_local'
ld: .tmp_vmlinux1: hidden symbol `__stack_chk_fail_local' isn't defined
ld: final link failed: Bad value
Makefile:1040: recipe for target 'vmlinux' failed
make: *** [vmlinux] Error 1

I don't have this issue with GCC 8.1, bootx_init.o has references to __stack_chk_fail, not to __stack_chk_fail_local

Looking online, it may be due to an old build and a lack of 'make clean', could it be the case here ?

Otherwise, can you retry the build to see if it's happen again ?

Christophe

Le 24/09/2018 Ã 17:15, Christophe Leroy a ÃcritÂ:
On PPC64, as register r13 points to the paca_struct at all time,
this patch adds a copy of the canary there, which is copied at
task_switch.
That new canary is then used by using the following GCC options:
-mstack-protector-guard=tls
-mstack-protector-guard-reg=r13
-mstack-protector-guard-offset=offsetof(struct paca_struct, canary))

Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
---
arch/powerpc/Kconfig | 2 +-
arch/powerpc/Makefile | 8 ++++++++
arch/powerpc/include/asm/paca.h | 3 +++
arch/powerpc/include/asm/stackprotector.h | 3 +++
arch/powerpc/kernel/asm-offsets.c | 3 +++
arch/powerpc/kernel/entry_64.S | 4 ++++
6 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 3bcb05929931..602eea723624 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -180,7 +180,7 @@ config PPC
select HAVE_ARCH_SECCOMP_FILTER
select HAVE_ARCH_TRACEHOOK
select HAVE_CBPF_JIT if !PPC64
- select HAVE_STACKPROTECTOR if $(cc-option,-mstack-protector-guard=tls) && PPC32
+ select HAVE_STACKPROTECTOR if $(cc-option,-mstack-protector-guard=tls)
select HAVE_CONTEXT_TRACKING if PPC64
select HAVE_DEBUG_KMEMLEAK
select HAVE_DEBUG_STACKOVERFLOW
diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index 45b8eb4d8fe7..81552c7b46eb 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -113,7 +113,11 @@ KBUILD_ARFLAGS += --target=elf$(BITS)-$(GNUTARGET)
endif
cflags-$(CONFIG_STACKPROTECTOR) += -mstack-protector-guard=tls
+ifdef CONFIG_PPC64
+cflags-$(CONFIG_STACKPROTECTOR) += -mstack-protector-guard-reg=r13
+else
cflags-$(CONFIG_STACKPROTECTOR) += -mstack-protector-guard-reg=r2
+endif
LDFLAGS_vmlinux-y := -Bstatic
LDFLAGS_vmlinux-$(CONFIG_RELOCATABLE) := -pie
@@ -411,8 +415,12 @@ ifdef CONFIG_STACKPROTECTOR
prepare: stack_protector_prepare
stack_protector_prepare: prepare0
+ifdef CONFIG_PPC64
+ $(eval KBUILD_CFLAGS += -mstack-protector-guard-offset=$(shell awk '{if ($$2 == "PACA_CANARY") print $$3;}' include/generated/asm-offsets.h))
+else
$(eval KBUILD_CFLAGS += -mstack-protector-guard-offset=$(shell awk '{if ($$2 == "TASK_CANARY") print $$3;}' include/generated/asm-offsets.h))
endif
+endif
# Use the file '.tmp_gas_check' for binutils tests, as gas won't output
# to stdout and these checks are run even on install targets.
diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h
index 6d6b3706232c..98d883e58945 100644
--- a/arch/powerpc/include/asm/paca.h
+++ b/arch/powerpc/include/asm/paca.h
@@ -246,6 +246,9 @@ struct paca_struct {
struct slb_entry *mce_faulty_slbs;
u16 slb_save_cache_ptr;
#endif /* CONFIG_PPC_BOOK3S_64 */
+#ifdef CONFIG_STACKPROTECTOR
+ unsigned long canary;
+#endif
} ____cacheline_aligned;
extern struct paca_struct **paca_ptrs;
diff --git a/arch/powerpc/include/asm/stackprotector.h b/arch/powerpc/include/asm/stackprotector.h
index 263e2aab1862..e81991955c0d 100644
--- a/arch/powerpc/include/asm/stackprotector.h
+++ b/arch/powerpc/include/asm/stackprotector.h
@@ -29,6 +29,9 @@ static __always_inline void boot_init_stack_canary(void)
canary ^= LINUX_VERSION_CODE;
current->stack_canary = canary;
+#ifdef CONFIG_PPC64
+ get_paca()->canary = canary;
+#endif
}
#endif /* _ASM_STACKPROTECTOR_H */
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index a992f7a53cf3..773dee55b3f6 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -81,6 +81,9 @@ int main(void)
OFFSET(MM, task_struct, mm);
#ifdef CONFIG_STACKPROTECTOR
OFFSET(TASK_CANARY, task_struct, stack_canary);
+#ifdef CONFIG_PPC64
+ OFFSET(PACA_CANARY, paca_struct, canary);
+#endif
#endif
OFFSET(MMCONTEXTID, mm_struct, context.id);
#ifdef CONFIG_PPC64
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 77a888bfcb53..573fa879d785 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -624,6 +624,10 @@ _GLOBAL(_switch)
addi r6,r4,-THREAD /* Convert THREAD to 'current' */
std r6,PACACURRENT(r13) /* Set new 'current' */
+#if defined(CONFIG_STACKPROTECTOR)
+ ld r6, TASK_CANARY(r6)
+ std r6, PACA_CANARY(r13)
+#endif
ld r8,KSP(r4) /* new stack pointer */
#ifdef CONFIG_PPC_BOOK3S_64