Commit c3ff2a51 authored by Christophe Leroy's avatar Christophe Leroy Committed by Michael Ellerman
Browse files

powerpc/32: add stack protector support 



This functionality was tentatively added in the past
(commit 6533b7c1 ("powerpc: Initial stack protector
(-fstack-protector) support")) but had to be reverted
(commit f2574030 ("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: default avatarChristophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent cd5ff945

arch/powerpc/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -180,6 +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_CONTEXT_TRACKING		if PPC64

	select HAVE_DEBUG_KMEMLEAK

	select HAVE_DEBUG_STACKOVERFLOW

arch/powerpc/Makefile

+10 −0
Original line number Diff line number Diff line
@@ -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

arch/powerpc/include/asm/stackprotector.h

0 → 100644
+34 −0
Original line number Diff line number Diff line 
/* 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 */

arch/powerpc/kernel/Makefile

+2 −0
Original line number Diff line number Diff line
@@ -20,6 +20,8 @@ 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)

arch/powerpc/kernel/asm-offsets.c

+3 −0
Original line number Diff line number Diff line
@@ -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);

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