4.19-stable review patch. If anyone has any objections, please let me know.
------------------
From: Christophe Leroy <christophe.leroy@xxxxxx>
[ Upstream commit c3ff2a5193fa61b1b284cfb1d79628814ed0e95a ]
This functionality was tentatively added in the past
(commit 6533b7c16ee5 ("powerpc: Initial stack protector
(-fstack-protector) support")) but had to be reverted
(commit f2574030b0e3 ("powerpc: Revert the initial stack
protector support") because of GCC implementing it differently
whether it had been built with libc support or not.
Now, GCC offers the possibility to manually set the
stack-protector mode (global or tls) regardless of libc support.
This time, the patch selects HAVE_STACKPROTECTOR only if
-mstack-protector-guard=tls is supported by GCC.
On PPC32, as register r2 points to current task_struct at
all time, the stack_canary located inside task_struct can be
used directly by using the following GCC options:
-mstack-protector-guard=tls
-mstack-protector-guard-reg=r2
-mstack-protector-guard-offset=offsetof(struct task_struct, stack_canary))
The protector is disabled for prom_init and bootx_init as
it is too early to handle it properly.
$ echo CORRUPT_STACK > /sys/kernel/debug/provoke-crash/DIRECT
[ 134.943666] Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: lkdtm_CORRUPT_STACK+0x64/0x64
[ 134.943666]
[ 134.955414] CPU: 0 PID: 283 Comm: sh Not tainted 4.18.0-s3k-dev-12143-ga3272be41209 #835
[ 134.963380] Call Trace:
[ 134.965860] [c6615d60] [c001f76c] panic+0x118/0x260 (unreliable)
[ 134.971775] [c6615dc0] [c001f654] panic+0x0/0x260
[ 134.976435] [c6615dd0] [c032c368] lkdtm_CORRUPT_STACK_STRONG+0x0/0x64
[ 134.982769] [c6615e00] [ffffffff] 0xffffffff
Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Stable-dep-of: 25ea739ea1d4 ("powerpc: Fail build if using recordmcount with binutils v2.37")
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
arch/powerpc/Kconfig | 1 +
arch/powerpc/Makefile | 10 +++++++
arch/powerpc/include/asm/stackprotector.h | 34 +++++++++++++++++++++++
arch/powerpc/kernel/Makefile | 2 ++
arch/powerpc/kernel/asm-offsets.c | 3 ++
arch/powerpc/platforms/powermac/Makefile | 1 +
6 files changed, 51 insertions(+)
create mode 100644 arch/powerpc/include/asm/stackprotector.h
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index f0e09d5f0bedd..3be56d857d57f 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -181,6 +181,7 @@ config PPC
select HAVE_ARCH_SECCOMP_FILTER
select HAVE_ARCH_TRACEHOOK
select HAVE_CBPF_JIT if !PPC64
+ select HAVE_STACKPROTECTOR if $(cc-option,-mstack-protector-guard=tls) && PPC32
select HAVE_CONTEXT_TRACKING if PPC64
select HAVE_DEBUG_KMEMLEAK
select HAVE_DEBUG_STACKOVERFLOW
diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index b2e0fd8735627..4cea663d5d49b 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -113,6 +113,9 @@ KBUILD_LDFLAGS += -m elf$(BITS)$(LDEMULATION)
KBUILD_ARFLAGS += --target=elf$(BITS)-$(GNUTARGET)
endif
+cflags-$(CONFIG_STACKPROTECTOR) += -mstack-protector-guard=tls
+cflags-$(CONFIG_STACKPROTECTOR) += -mstack-protector-guard-reg=r2
+
LDFLAGS_vmlinux-y := -Bstatic
LDFLAGS_vmlinux-$(CONFIG_RELOCATABLE) := -pie
LDFLAGS_vmlinux := $(LDFLAGS_vmlinux-y)
@@ -419,6 +422,13 @@ archclean:
archprepare: checkbin
+ifdef CONFIG_STACKPROTECTOR
+prepare: stack_protector_prepare
+
+stack_protector_prepare: prepare0
+ $(eval KBUILD_CFLAGS += -mstack-protector-guard-offset=$(shell awk '{if ($$2 == "TASK_CANARY") print $$3;}' include/generated/asm-offsets.h))
+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.
TOUT := .tmp_gas_check
diff --git a/arch/powerpc/include/asm/stackprotector.h b/arch/powerpc/include/asm/stackprotector.h
new file mode 100644
index 0000000000000..d05d969c98c21
--- /dev/null
+++ b/arch/powerpc/include/asm/stackprotector.h
@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * GCC stack protector support.
+ *
+ */
+
+#ifndef _ASM_STACKPROTECTOR_H
+#define _ASM_STACKPROTECTOR_H
+
+#include <linux/random.h>
+#include <linux/version.h>
+#include <asm/reg.h>
+#include <asm/current.h>
+
+/*
+ * Initialize the stackprotector canary value.
+ *
+ * NOTE: this must only be called from functions that never return,
+ * and it must always be inlined.
+ */
+static __always_inline void boot_init_stack_canary(void)
+{
+ unsigned long canary;
+
+ /* Try to get a semi random initial value. */
+ canary = get_random_canary();
+ canary ^= mftb();
+ canary ^= LINUX_VERSION_CODE;
+ canary &= CANARY_MASK;
+
+ current->stack_canary = canary;
+}
+
+#endif /* _ASM_STACKPROTECTOR_H */
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index bf19c5514d6c2..cccea292af683 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -21,6 +21,8 @@ CFLAGS_prom_init.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
CFLAGS_btext.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
CFLAGS_prom.o += $(DISABLE_LATENT_ENTROPY_PLUGIN)
+CFLAGS_prom_init.o += $(call cc-option, -fno-stack-protector)
+
ifdef CONFIG_FUNCTION_TRACER
# Do not trace early boot code
CFLAGS_REMOVE_cputable.o = $(CC_FLAGS_FTRACE)
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index 50400f213bbf2..c2288c73d56d1 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -79,6 +79,9 @@ int main(void)
{
OFFSET(THREAD, task_struct, thread);
OFFSET(MM, task_struct, mm);
+#ifdef CONFIG_STACKPROTECTOR
+ OFFSET(TASK_CANARY, task_struct, stack_canary);
+#endif
OFFSET(MMCONTEXTID, mm_struct, context.id);
#ifdef CONFIG_PPC64
DEFINE(SIGSEGV, SIGSEGV);
diff --git a/arch/powerpc/platforms/powermac/Makefile b/arch/powerpc/platforms/powermac/Makefile
index 561a67d65e4d4..923bfb3404333 100644
--- a/arch/powerpc/platforms/powermac/Makefile
+++ b/arch/powerpc/platforms/powermac/Makefile
@@ -1,5 +1,6 @@
# SPDX-License-Identifier: GPL-2.0
CFLAGS_bootx_init.o += -fPIC
+CFLAGS_bootx_init.o += $(call cc-option, -fno-stack-protector)
ifdef CONFIG_FUNCTION_TRACER
# Do not trace early boot code
--
2.40.1
