diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 91be74d8df658ccd5a4701fe7438053115dceeb9..5c0305585a0a24074a9af78f69e47d6efc87c3c7 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1810,6 +1810,21 @@ config XEN
help
Say Y if you want to run Linux in a Virtual Machine on Xen on ARM.
+config STACKPROTECTOR_PER_TASK
+ bool "Use a unique stack canary value for each task"
+ depends on GCC_PLUGINS && STACKPROTECTOR && SMP && !XIP_DEFLATED_DATA
+ select GCC_PLUGIN_ARM_SSP_PER_TASK
+ default y
+ help
+ Due to the fact that GCC uses an ordinary symbol reference from
+ which to load the value of the stack canary, this value can only
+ change at reboot time on SMP systems, and all tasks running in the
+ kernel's address space are forced to use the same canary value for
+ the entire duration that the system is up.
+
+ Enable this option to switch to a different method that uses a
+ different canary value for each task.
+
endmenu
menu "Boot options"
diff --git a/arch/arm/Makefile b/arch/arm/Makefile
index 05a91d8b89f357b389921eb66aa2591a043526bf..0436002d509190c38fd6d037967b0ebf4df9a4f7 100644
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -303,6 +303,18 @@ else
KBUILD_IMAGE := $(boot)/zImage
endif
+ifeq ($(CONFIG_STACKPROTECTOR_PER_TASK),y)
+prepare: stack_protector_prepare
+stack_protector_prepare: prepare0
+ $(eval KBUILD_CFLAGS += \
+ -fplugin-arg-arm_ssp_per_task_plugin-tso=$(shell \
+ awk '{if ($$2 == "THREAD_SZ_ORDER") print $$3;}'\
+ include/generated/asm-offsets.h) \
+ -fplugin-arg-arm_ssp_per_task_plugin-offset=$(shell \
+ awk '{if ($$2 == "TI_STACK_CANARY") print $$3;}'\
+ include/generated/asm-offsets.h))
+endif
+
all: $(notdir $(KBUILD_IMAGE))
diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
index 1f5a5ffe7fcf84b5da64bc74747c50384f5bfeea..01bf2585a0fa08f0dfe4ff35167f4526d183c61f 100644
--- a/arch/arm/boot/compressed/Makefile
+++ b/arch/arm/boot/compressed/Makefile
@@ -101,6 +101,7 @@ clean-files += piggy_data lib1funcs.S ashldi3.S bswapsdi2.S \
$(libfdt) $(libfdt_hdrs) hyp-stub.S
KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
+KBUILD_CFLAGS += $(DISABLE_ARM_SSP_PER_TASK_PLUGIN)
ifeq ($(CONFIG_FUNCTION_TRACER),y)
ORIG_CFLAGS := $(KBUILD_CFLAGS)
diff --git a/arch/arm/include/asm/stackprotector.h b/arch/arm/include/asm/stackprotector.h
index ef5f7b69443ec59e752038394b4ab6a4f12fe819..72a20c3a0a90b2121952161ed3839274ebf8c44a 100644
--- a/arch/arm/include/asm/stackprotector.h
+++ b/arch/arm/include/asm/stackprotector.h
@@ -6,8 +6,10 @@
* the stack frame and verifying that it hasn't been overwritten when
* returning from the function. The pattern is called stack canary
* and gcc expects it to be defined by a global variable called
- * "__stack_chk_guard" on ARM. This unfortunately means that on SMP
- * we cannot have a different canary value per task.
+ * "__stack_chk_guard" on ARM. This prevents SMP systems from using a
+ * different value for each task unless we enable a GCC plugin that
+ * replaces these symbol references with references to each task's own
+ * value.
*/
#ifndef _ASM_STACKPROTECTOR_H
@@ -16,6 +18,8 @@
#include <linux/random.h>
#include <linux/version.h>
+#include <asm/thread_info.h>
+
extern unsigned long __stack_chk_guard;
/*
@@ -33,7 +37,11 @@ static __always_inline void boot_init_stack_canary(void)
canary ^= LINUX_VERSION_CODE;
current->stack_canary = canary;
+#ifndef CONFIG_STACKPROTECTOR_PER_TASK
__stack_chk_guard = current->stack_canary;
+#else
+ current_thread_info()->stack_canary = current->stack_canary;
+#endif
}
#endif /* _ASM_STACKPROTECTOR_H */
diff --git a/arch/arm/include/asm/thread_info.h b/arch/arm/include/asm/thread_info.h
index 8f55dc520a3e5512cd1474f4a5c3c2d7e72698e8..286eb61c632bead2fa16b8590b0915f3269f40a7 100644
--- a/arch/arm/include/asm/thread_info.h
+++ b/arch/arm/include/asm/thread_info.h
@@ -53,6 +53,9 @@ struct thread_info {
struct task_struct *task; /* main task structure */
__u32 cpu; /* cpu */
__u32 cpu_domain; /* cpu domain */
+#ifdef CONFIG_STACKPROTECTOR_PER_TASK
+ unsigned long stack_canary;
+#endif
struct cpu_context_save cpu_context; /* cpu context */
__u32 syscall; /* syscall number */
__u8 used_cp[16]; /* thread used copro */
diff --git a/arch/arm/kernel/asm-offsets.c b/arch/arm/kernel/asm-offsets.c
index 3968d6c22455be5057909ea4d928f7ee0054e1a2..28b27104ac0c62fb5db1ef8469ccb8492dbee007 100644
--- a/arch/arm/kernel/asm-offsets.c
+++ b/arch/arm/kernel/asm-offsets.c
@@ -79,6 +79,10 @@ int main(void)
#ifdef CONFIG_CRUNCH
DEFINE(TI_CRUNCH_STATE, offsetof(struct thread_info, crunchstate));
#endif
+#ifdef CONFIG_STACKPROTECTOR_PER_TASK
+ DEFINE(TI_STACK_CANARY, offsetof(struct thread_info, stack_canary));
+#endif
+ DEFINE(THREAD_SZ_ORDER, THREAD_SIZE_ORDER);
BLANK();
DEFINE(S_R0, offsetof(struct pt_regs, ARM_r0));
DEFINE(S_R1, offsetof(struct pt_regs, ARM_r1));
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 82ab015bf42b7bf263cd13d61274e6f4e899d9db..16601d1442d1767b4498442b8454a31afb34268d 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -39,7 +39,7 @@
#include <asm/tls.h>
#include <asm/vdso.h>
-#ifdef CONFIG_STACKPROTECTOR
+#if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_STACKPROTECTOR_PER_TASK)
#include <linux/stackprotector.h>
unsigned long __stack_chk_guard __read_mostly;
EXPORT_SYMBOL(__stack_chk_guard);
@@ -267,6 +267,10 @@ copy_thread(unsigned long clone_flags, unsigned long stack_start,
thread_notify(THREAD_NOTIFY_COPY, thread);
+#ifdef CONFIG_STACKPROTECTOR_PER_TASK
+ thread->stack_canary = p->stack_canary;
+#endif
+
return 0;
}
diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins
index 46c5c680980657dfc8997d5127bfab198b710490..048179d8c07fc1646e446b7d4fa550b257dcb396 100644
--- a/scripts/Makefile.gcc-plugins
+++ b/scripts/Makefile.gcc-plugins
@@ -36,6 +36,12 @@ ifdef CONFIG_GCC_PLUGIN_STACKLEAK
endif
export DISABLE_STACKLEAK_PLUGIN
+gcc-plugin-$(CONFIG_GCC_PLUGIN_ARM_SSP_PER_TASK) += arm_ssp_per_task_plugin.so
+ifdef CONFIG_GCC_PLUGIN_ARM_SSP_PER_TASK
+ DISABLE_ARM_SSP_PER_TASK_PLUGIN += -fplugin-arg-arm_ssp_per_task_plugin-disable
+endif
+export DISABLE_ARM_SSP_PER_TASK_PLUGIN
+
# All the plugin CFLAGS are collected here in case a build target needs to
# filter them out of the KBUILD_CFLAGS.
GCC_PLUGINS_CFLAGS := $(strip $(addprefix -fplugin=$(objtree)/scripts/gcc-plugins/, $(gcc-plugin-y)) $(gcc-plugin-cflags-y))
diff --git a/scripts/gcc-plugins/Kconfig b/scripts/gcc-plugins/Kconfig
index 0d5c799688f0ae31fa02f82dc8451ad1a5811ff5..d45f7f36b859a55aac1192de6072ca3870085581 100644
--- a/scripts/gcc-plugins/Kconfig
+++ b/scripts/gcc-plugins/Kconfig
@@ -190,4 +190,8 @@ config STACKLEAK_RUNTIME_DISABLE
runtime to control kernel stack erasing for kernels built with
CONFIG_GCC_PLUGIN_STACKLEAK.
+config GCC_PLUGIN_ARM_SSP_PER_TASK
+ bool
+ depends on GCC_PLUGINS && ARM
+
endif
diff --git a/scripts/gcc-plugins/arm_ssp_per_task_plugin.c b/scripts/gcc-plugins/arm_ssp_per_task_plugin.c
new file mode 100644
index 0000000000000000000000000000000000000000..de70b8470971e8929a5949174c48a84ab774e0b7
--- /dev/null
+++ b/scripts/gcc-plugins/arm_ssp_per_task_plugin.c
@@ -0,0 +1,103 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "gcc-common.h"
+
+__visible int plugin_is_GPL_compatible;
+
+static unsigned int sp_mask, canary_offset;
+
+static unsigned int arm_pertask_ssp_rtl_execute(void)
+{
+ rtx_insn *insn;
+
+ for (insn = get_insns(); insn; insn = NEXT_INSN(insn)) {
+ const char *sym;
+ rtx body;
+ rtx masked_sp;
+
+ /*
+ * Find a SET insn involving a SYMBOL_REF to __stack_chk_guard
+ */
+ if (!INSN_P(insn))
+ continue;
+ body = PATTERN(insn);
+ if (GET_CODE(body) != SET ||
+ GET_CODE(SET_SRC(body)) != SYMBOL_REF)
+ continue;
+ sym = XSTR(SET_SRC(body), 0);
+ if (strcmp(sym, "__stack_chk_guard"))
+ continue;
+
+ /*
+ * Replace the source of the SET insn with an expression that
+ * produces the address of the copy of the stack canary value
+ * stored in struct thread_info
+ */
+ masked_sp = gen_reg_rtx(Pmode);
+
+ emit_insn_before(gen_rtx_SET(masked_sp,
+ gen_rtx_AND(Pmode,
+ stack_pointer_rtx,
+ GEN_INT(sp_mask))),
+ insn);
+
+ SET_SRC(body) = gen_rtx_PLUS(Pmode, masked_sp,
+ GEN_INT(canary_offset));
+ }
+ return 0;
+}
+
+#define PASS_NAME arm_pertask_ssp_rtl
+
+#define NO_GATE
+#include "gcc-generate-rtl-pass.h"
+
+__visible int plugin_init(struct plugin_name_args *plugin_info,
+ struct plugin_gcc_version *version)
+{
+ const char * const plugin_name = plugin_info->base_name;
+ const int argc = plugin_info->argc;
+ const struct plugin_argument *argv = plugin_info->argv;
+ int tso = 0;
+ int i;
+
+ if (!plugin_default_version_check(version, &gcc_version)) {
+ error(G_("incompatible gcc/plugin versions"));
+ return 1;
+ }
+
+ for (i = 0; i < argc; ++i) {
+ if (!strcmp(argv[i].key, "disable"))
+ return 0;
+
+ /* all remaining options require a value */
+ if (!argv[i].value) {
+ error(G_("no value supplied for option '-fplugin-arg-%s-%s'"),
+ plugin_name, argv[i].key);
+ return 1;
+ }
+
+ if (!strcmp(argv[i].key, "tso")) {
+ tso = atoi(argv[i].value);
+ continue;
+ }
+
+ if (!strcmp(argv[i].key, "offset")) {
+ canary_offset = atoi(argv[i].value);
+ continue;
+ }
+ error(G_("unknown option '-fplugin-arg-%s-%s'"),
+ plugin_name, argv[i].key);
+ return 1;
+ }
+
+ /* create the mask that produces the base of the stack */
+ sp_mask = ~((1U << (12 + tso)) - 1);
+
+ PASS_INFO(arm_pertask_ssp_rtl, "expand", 1, PASS_POS_INSERT_AFTER);
+
+ register_callback(plugin_info->base_name, PLUGIN_PASS_MANAGER_SETUP,
+ NULL, &arm_pertask_ssp_rtl_pass_info);
+
+ return 0;
+}