Commit a6ede084 authored by Zong Li's avatar Zong Li Committed by Paul Walmsley
Browse files

riscv: cfi: clear CFI lock status in start_thread() 



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: default avatarZong Li <zong.li@sifive.com>
Link: https://patch.msgid.link/20260323065640.4045713-1-zong.li@sifive.com


[pjw@kernel.org: ensure we unlock before changing state; cleaned up subject line]
Signed-off-by: default avatarPaul Walmsley <pjw@kernel.org>
parent a621d9cd

arch/riscv/include/asm/usercfi.h

+4 −4
Original line number Diff line number Diff line
@@ -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

arch/riscv/kernel/process.c

+2 −0
Original line number Diff line number Diff line
@@ -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

arch/riscv/kernel/usercfi.c

+6 −6
Original line number Diff line number Diff line
@@ -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;

}