[RFC PATCH] generic_entry: Add stackleak support

[guoren at kernel.org]

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

Make generic_entry supports basic STACKLEAK, and no arch custom
code is needed.

Signed-off-by: Guo Ren <guoren at linux.alibaba.com>
Signed-off-by: Guo Ren <guoren at kernel.org>
---
 drivers/firmware/efi/libstub/Makefile | 4 +++-
 include/linux/stackleak.h             | 3 +++
 kernel/entry/common.c                 | 5 +++++
 security/Kconfig.hardening            | 2 +-
 4 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
index d0537573501e..bb6ad37a9690 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -19,7 +19,7 @@ cflags-$(CONFIG_X86)		+= -m$(BITS) -D__KERNEL__ \
 # arm64 uses the full KBUILD_CFLAGS so it's necessary to explicitly
 # disable the stackleak plugin
 cflags-$(CONFIG_ARM64)		:= $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
-				   -fpie $(DISABLE_STACKLEAK_PLUGIN) \
+				   -fpie \
 				   $(call cc-option,-mbranch-protection=none)
 cflags-$(CONFIG_ARM)		:= $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
 				   -fno-builtin -fpic \
@@ -27,6 +27,8 @@ cflags-$(CONFIG_ARM)		:= $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
 cflags-$(CONFIG_RISCV)		:= $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
 				   -fpic
 
+cflags-$(CONFIG_GCC_PLUGIN_STACKLEAK) += $(DISABLE_STACKLEAK_PLUGIN)
+
 cflags-$(CONFIG_EFI_GENERIC_STUB) += -I$(srctree)/scripts/dtc/libfdt
 
 KBUILD_CFLAGS			:= $(cflags-y) -Os -DDISABLE_BRANCH_PROFILING \
diff --git a/include/linux/stackleak.h b/include/linux/stackleak.h
index c36e7a3b45e7..9890802a5868 100644
--- a/include/linux/stackleak.h
+++ b/include/linux/stackleak.h
@@ -76,8 +76,11 @@ static inline void stackleak_task_init(struct task_struct *t)
 # endif
 }
 
+void noinstr stackleak_erase(void);
+
 #else /* !CONFIG_GCC_PLUGIN_STACKLEAK */
 static inline void stackleak_task_init(struct task_struct *t) { }
+static inline void stackleak_erase(void) {}
 #endif
 
 #endif
diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index 063068a9ea9b..6acb1d6a1396 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -8,6 +8,7 @@
 #include <linux/livepatch.h>
 #include <linux/audit.h>
 #include <linux/tick.h>
+#include <linux/stackleak.h>
 
 #include "common.h"
 
@@ -194,6 +195,10 @@ static void exit_to_user_mode_prepare(struct pt_regs *regs)
 
 	lockdep_assert_irqs_disabled();
 
+#ifndef CONFIG_HAVE_ARCH_STACKLEAK
+	stackleak_erase();
+#endif
+
 	/* Flush pending rcuog wakeup before the last need_resched() check */
 	tick_nohz_user_enter_prepare();
 
diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening
index bd2aabb2c60f..3329482beb8d 100644
--- a/security/Kconfig.hardening
+++ b/security/Kconfig.hardening
@@ -152,7 +152,7 @@ config GCC_PLUGIN_STRUCTLEAK_VERBOSE
 config GCC_PLUGIN_STACKLEAK
 	bool "Poison kernel stack before returning from syscalls"
 	depends on GCC_PLUGINS
-	depends on HAVE_ARCH_STACKLEAK
+	depends on HAVE_ARCH_STACKLEAK || GENERIC_ENTRY
 	help
 	  This option makes the kernel erase the kernel stack before
 	  returning from system calls. This has the effect of leaving
-- 
2.36.1