[PATCH] riscv: Add STACKPROTECTOR supported

[guoren@kernel.org]

From: Guo Ren <guoren@linux.alibaba.com>

The -fstack-protector & -fstack-protector-strong features are from
gcc. The patch only add basic kernel support to stack-protector
feature and some arch could have its own solution such as
ARM64_PTR_AUTH.

After enabling STACKPROTECTOR and STACKPROTECTOR_STRONG, the .text
size is expanded from  0x7de066 to 0x81fb32 (only 5%) to add canary
checking code.

Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Palmer Dabbelt <palmerdabbelt@google.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Björn Töpel <bjorn.topel@gmail.com>
Cc: Greentime Hu <green.hu@gmail.com>
Cc: Atish Patra <atish.patra@wdc.com>
---
 arch/riscv/Kconfig                      |  1 +
 arch/riscv/include/asm/stackprotector.h | 29 +++++++++++++++++++++++++++++
 arch/riscv/kernel/process.c             |  6 ++++++
 3 files changed, 36 insertions(+)
 create mode 100644 arch/riscv/include/asm/stackprotector.h

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index f927a91..4b0e308 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -63,6 +63,7 @@ config RISCV
 	select HAVE_PERF_EVENTS
 	select HAVE_PERF_REGS
 	select HAVE_PERF_USER_STACK_DUMP
+	select HAVE_STACKPROTECTOR
 	select HAVE_SYSCALL_TRACEPOINTS
 	select IRQ_DOMAIN
 	select MODULES_USE_ELF_RELA if MODULES
diff --git a/arch/riscv/include/asm/stackprotector.h b/arch/riscv/include/asm/stackprotector.h
new file mode 100644
index 00000000..5962f88
--- /dev/null
+++ b/arch/riscv/include/asm/stackprotector.h
@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _ASM_RISCV_STACKPROTECTOR_H
+#define _ASM_RISCV_STACKPROTECTOR_H
+
+#include <linux/random.h>
+#include <linux/version.h>
+
+extern unsigned long __stack_chk_guard;
+
+/*
+ * 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. */
+	get_random_bytes(&canary, sizeof(canary));
+	canary ^= LINUX_VERSION_CODE;
+	canary &= CANARY_MASK;
+
+	current->stack_canary = canary;
+	__stack_chk_guard = current->stack_canary;
+}
+#endif /* _ASM_RISCV_STACKPROTECTOR_H */
diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index 824d117..6548929 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -24,6 +24,12 @@
 
 register unsigned long gp_in_global __asm__("gp");
 
+#ifdef CONFIG_STACKPROTECTOR
+#include <linux/stackprotector.h>
+unsigned long __stack_chk_guard __read_mostly;
+EXPORT_SYMBOL(__stack_chk_guard);
+#endif
+
 extern asmlinkage void ret_from_fork(void);
 extern asmlinkage void ret_from_kernel_thread(void);
 
-- 
2.7.4