[PATCH 2/6] riscv: cfi: clear CFI lock status in start_thread()

[Paul Walmsley]

From: Zong Li <zong.li@xxxxxxxxxx>

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

A newly execd address space 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>
Link: https://patch.msgid.link/20260323065640.4045713-1-zong.li@xxxxxxxxxx
[pjw@xxxxxxxxxx: ensure we unlock before changing state; cleaned up subject line]
Signed-off-by: Paul Walmsley <pjw@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 7495baae1e3c..f56966edbf5c 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 5957effab57c..b2df7f72241a 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -160,6 +160,7 @@ void start_thread(struct pt_regs *regs, unsigned long pc,
 	 * clear shadow stack state on exec.
 	 * libc will set it later via prctl.
 	 */
+	set_shstk_lock(current, false);
 	set_shstk_status(current, false);
 	set_shstk_base(current, 0, 0);
 	set_active_shstk(current, 0);
@@ -167,6 +168,7 @@ void start_thread(struct pt_regs *regs, unsigned long pc,
 	 * disable indirect branch tracking on exec.
 	 * libc will enable it later via prctl.
 	 */
+	set_indir_lp_lock(current, false);
 	set_indir_lp_status(current, false);
 
 #ifdef CONFIG_64BIT
diff --git a/arch/riscv/kernel/usercfi.c b/arch/riscv/kernel/usercfi.c
index 1adba746f164..9052171c1a8c 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;
 }