From c3ff2a5193fa61b1b284cfb1d79628814ed0e95a Mon Sep 17 00:00:00 2001 From: Christophe Leroy Date: Thu, 27 Sep 2018 07:05:53 +0000 Subject: powerpc/32: add stack protector support 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 Signed-off-by: Michael Ellerman --- arch/powerpc/Makefile | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'arch/powerpc/Makefile') diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile index 07d9dce7eda6..45b8eb4d8fe7 100644 --- a/arch/powerpc/Makefile +++ b/arch/powerpc/Makefile @@ -112,6 +112,9 @@ 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) @@ -404,6 +407,13 @@ 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 -- cgit