[PATCH] riscv: cif: clear CFI lock status in start_thread

[Zong Li]

When libc locks the CFI status through the following prctl:
 - PR_LOCK_SHADOW_STACK_STATUS
 - PR_LOCK_INDIR_BR_LP_STATUS

A newly forked process will inherit the lock status if it
does not clear the lock bits. Since the lock bits remain
set, libc will later fail to enable the landing pad and
shadow stack.

Signed-off-by: Zong Li <zong.li@xxxxxxxxxx>
---
 arch/riscv/include/asm/usercfi.h |  8 ++++----
 arch/riscv/kernel/process.c      |  2 ++
 arch/riscv/kernel/usercfi.c      | 12 ++++++------
 3 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/arch/riscv/include/asm/usercfi.h b/arch/riscv/include/asm/usercfi.h
index f7fa9d602aae..c4ab11378308 100644
--- a/arch/riscv/include/asm/usercfi.h
+++ b/arch/riscv/include/asm/usercfi.h
@@ -39,7 +39,7 @@ void set_active_shstk(struct task_struct *task, unsigned long shstk_addr);
 bool is_shstk_enabled(struct task_struct *task);
 bool is_shstk_locked(struct task_struct *task);
 bool is_shstk_allocated(struct task_struct *task);
-void set_shstk_lock(struct task_struct *task);
+void set_shstk_lock(struct task_struct *task, bool lock);
 void set_shstk_status(struct task_struct *task, bool enable);
 unsigned long get_active_shstk(struct task_struct *task);
 int restore_user_shstk(struct task_struct *tsk, unsigned long shstk_ptr);
@@ -47,7 +47,7 @@ int save_user_shstk(struct task_struct *tsk, unsigned long *saved_shstk_ptr);
 bool is_indir_lp_enabled(struct task_struct *task);
 bool is_indir_lp_locked(struct task_struct *task);
 void set_indir_lp_status(struct task_struct *task, bool enable);
-void set_indir_lp_lock(struct task_struct *task);
+void set_indir_lp_lock(struct task_struct *task, bool lock);
 
 #define PR_SHADOW_STACK_SUPPORTED_STATUS_MASK (PR_SHADOW_STACK_ENABLE)
 
@@ -69,7 +69,7 @@ void set_indir_lp_lock(struct task_struct *task);
 
 #define is_shstk_allocated(task) false
 
-#define set_shstk_lock(task) do {} while (0)
+#define set_shstk_lock(task, lock) do {} while (0)
 
 #define set_shstk_status(task, enable) do {} while (0)
 
@@ -79,7 +79,7 @@ void set_indir_lp_lock(struct task_struct *task);
 
 #define set_indir_lp_status(task, enable) do {} while (0)
 
-#define set_indir_lp_lock(task) do {} while (0)
+#define set_indir_lp_lock(task, lock) do {} while (0)
 
 #define restore_user_shstk(tsk, shstk_ptr) -EINVAL
 
diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index 6b3648256a0f..36bac478f1e1 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -164,11 +164,13 @@ void start_thread(struct pt_regs *regs, unsigned long pc,
 	set_shstk_status(current, false);
 	set_shstk_base(current, 0, 0);
 	set_active_shstk(current, 0);
+	set_shstk_lock(current, false);
 	/*
 	 * disable indirect branch tracking on exec.
 	 * libc will enable it later via prctl.
 	 */
 	set_indir_lp_status(current, false);
+	set_indir_lp_lock(current, false);
 
 #ifdef CONFIG_64BIT
 	regs->status &= ~SR_UXL;
diff --git a/arch/riscv/kernel/usercfi.c b/arch/riscv/kernel/usercfi.c
index a8530e6afb1e..a101e317fe5e 100644
--- a/arch/riscv/kernel/usercfi.c
+++ b/arch/riscv/kernel/usercfi.c
@@ -74,9 +74,9 @@ void set_shstk_status(struct task_struct *task, bool enable)
 	csr_write(CSR_ENVCFG, task->thread.envcfg);
 }
 
-void set_shstk_lock(struct task_struct *task)
+void set_shstk_lock(struct task_struct *task, bool lock)
 {
-	task->thread_info.user_cfi_state.ubcfi_locked = 1;
+	task->thread_info.user_cfi_state.ubcfi_locked = lock;
 }
 
 bool is_indir_lp_enabled(struct task_struct *task)
@@ -104,9 +104,9 @@ void set_indir_lp_status(struct task_struct *task, bool enable)
 	csr_write(CSR_ENVCFG, task->thread.envcfg);
 }
 
-void set_indir_lp_lock(struct task_struct *task)
+void set_indir_lp_lock(struct task_struct *task, bool lock)
 {
-	task->thread_info.user_cfi_state.ufcfi_locked = 1;
+	task->thread_info.user_cfi_state.ufcfi_locked = lock;
 }
 /*
  * If size is 0, then to be compatible with regular stack we want it to be as big as
@@ -452,7 +452,7 @@ int arch_lock_shadow_stack_status(struct task_struct *task,
 	    !is_shstk_enabled(task) || arg != 0)
 		return -EINVAL;
 
-	set_shstk_lock(task);
+	set_shstk_lock(task, true);
 
 	return 0;
 }
@@ -502,7 +502,7 @@ int arch_lock_indir_br_lp_status(struct task_struct *task,
 	    !is_indir_lp_enabled(task) || arg != 0)
 		return -EINVAL;
 
-	set_indir_lp_lock(task);
+	set_indir_lp_lock(task, true);
 
 	return 0;
 }
-- 
2.43.7