[PATCH] arch/riscv: Add support for STACKLEAK gcc plugin

[Dao Lu]

This adds support for STACKLEAK gcc plugin to ricv by implementing
stackleak_check_alloca, based heavily on the arm64 version, and adding
the two helpers used by the stackleak common code:
current_top_of_stack() and on_thread_stack(). This also adds the missing
helper functions for riscv, on_stack() and on_task_stack().
Additionally, this disables the plugin for EFI stub code for riscv.

Signed-off-by: Dao Lu <daolu at rivosinc.com>
---
 arch/riscv/Kconfig                    |  1 +
 arch/riscv/include/asm/processor.h    | 18 ++++++++++++++++++
 arch/riscv/include/asm/stacktrace.h   | 27 +++++++++++++++++++++++++++
 arch/riscv/kernel/entry.S             |  3 +++
 drivers/firmware/efi/libstub/Makefile |  2 +-
 5 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index c22f58155948..22aa146acd25 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -80,6 +80,7 @@ config RISCV
 	select HAVE_ARCH_MMAP_RND_BITS if MMU
 	select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
 	select HAVE_ARCH_SECCOMP_FILTER
+	select HAVE_ARCH_STACKLEAK
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE if 64BIT && MMU
 	select ARCH_ENABLE_THP_MIGRATION if TRANSPARENT_HUGEPAGE
diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
index 21c8072dce17..3a7505ab7f58 100644
--- a/arch/riscv/include/asm/processor.h
+++ b/arch/riscv/include/asm/processor.h
@@ -85,6 +85,24 @@ int riscv_of_parent_hartid(struct device_node *node);
 extern void riscv_fill_hwcap(void);
 extern int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src);
 
+/*
+ * For CONFIG_GCC_PLUGIN_STACKLEAK
+ *
+ * These need to be macros because otherwise we get stuck in a nightmare
+ * of header definitions for the use of task_stack_page.
+ */
+
+struct stack_info {
+	unsigned long low;
+	unsigned long high;
+};
+
+/*
+ * The top of the current task's task stack
+ */
+#define current_top_of_stack()	((unsigned long)current->stack + THREAD_SIZE)
+#define on_thread_stack()	(on_task_stack(current, current_stack_pointer, 1, NULL))
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* _ASM_RISCV_PROCESSOR_H */
diff --git a/arch/riscv/include/asm/stacktrace.h b/arch/riscv/include/asm/stacktrace.h
index 3450c1912afd..afb66b677b6a 100644
--- a/arch/riscv/include/asm/stacktrace.h
+++ b/arch/riscv/include/asm/stacktrace.h
@@ -16,4 +16,31 @@ extern void notrace walk_stackframe(struct task_struct *task, struct pt_regs *re
 extern void dump_backtrace(struct pt_regs *regs, struct task_struct *task,
 			   const char *loglvl);
 
+static inline bool on_stack(unsigned long sp, unsigned long size,
+			    unsigned long low, unsigned long high,
+			    struct stack_info *info)
+{
+	if (!low)
+		return false;
+
+	if (sp < low || sp + size < sp || sp + size > high)
+		return false;
+
+	if (info) {
+		info->low = low;
+		info->high = high;
+	}
+	return true;
+}
+
+static inline bool on_task_stack(const struct task_struct *tsk,
+				 unsigned long sp, unsigned long size,
+				 struct stack_info *info)
+{
+	unsigned long low = (unsigned long)task_stack_page(tsk);
+	unsigned long high = low + THREAD_SIZE;
+
+	return on_stack(sp, size, low, high, info);
+}
+
 #endif /* _ASM_RISCV_STACKTRACE_H */
diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
index 2e5b88ca11ce..65d441cb560f 100644
--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -264,6 +264,9 @@ ret_from_exception:
 	bnez s0, resume_kernel
 
 resume_userspace:
+#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
+	call stackleak_erase
+#endif
 	/* Interrupts must be disabled here so flags are checked atomically */
 	REG_L s0, TASK_TI_FLAGS(tp) /* current_thread_info->flags */
 	andi s1, s0, _TIF_WORK_MASK
diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
index d0537573501e..5e1fc4f82883 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -25,7 +25,7 @@ cflags-$(CONFIG_ARM)		:= $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
 				   -fno-builtin -fpic \
 				   $(call cc-option,-mno-single-pic-base)
 cflags-$(CONFIG_RISCV)		:= $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
-				   -fpic
+				   -fpic $(DISABLE_STACKLEAK_PLUGIN)
 
 cflags-$(CONFIG_EFI_GENERIC_STUB) += -I$(srctree)/scripts/dtc/libfdt
 
-- 
2.25.1