Commit 8a9e22d2 authored by Deepak Gupta's avatar Deepak Gupta Committed by Paul Walmsley
Browse files

riscv: Implement indirect branch tracking prctls 



This patch adds a RISC-V implementation of the following prctls:
PR_SET_INDIR_BR_LP_STATUS, PR_GET_INDIR_BR_LP_STATUS and
PR_LOCK_INDIR_BR_LP_STATUS.

Reviewed-by: default avatarZong Li <zong.li@sifive.com>
Signed-off-by: default avatarDeepak Gupta <debug@rivosinc.com>
Tested-by: default avatarAndreas Korb <andreas.korb@aisec.fraunhofer.de>
Tested-by: default avatarValentin Haudiquet <valentin.haudiquet@canonical.com>
Link: https://patch.msgid.link/20251112-v5_user_cfi_series-v23-14-b55691eacf4f@rivosinc.com


[pjw@kernel.org: clean up patch description]
Signed-off-by: default avatarPaul Walmsley <pjw@kernel.org>
parent 5ca243f6

arch/riscv/include/asm/usercfi.h

+14 −0
Original line number Diff line number Diff line
@@ -16,6 +16,8 @@ struct kernel_clone_args; 
struct cfi_state {

	unsigned long ubcfi_en : 1; /* Enable for backward cfi. */

	unsigned long ubcfi_locked : 1;

	unsigned long ufcfi_en : 1; /* Enable for forward cfi. Note that ELP goes in sstatus */

	unsigned long ufcfi_locked : 1;

	unsigned long user_shdw_stk; /* Current user shadow stack pointer */

	unsigned long shdw_stk_base; /* Base address of shadow stack */

	unsigned long shdw_stk_size; /* size of shadow stack */
@@ -32,6 +34,10 @@ 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_status(struct task_struct *task, bool enable);

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);



#define PR_SHADOW_STACK_SUPPORTED_STATUS_MASK (PR_SHADOW_STACK_ENABLE)
@@ -57,6 +63,14 @@ void set_shstk_status(struct task_struct *task, bool enable); 


#define set_shstk_status(task, enable) do {} while (0)



#define is_indir_lp_enabled(task) false



#define is_indir_lp_locked(task) false



#define set_indir_lp_status(task, enable) do {} while (0)



#define set_indir_lp_lock(task) do {} while (0)



#endif /* CONFIG_RISCV_USER_CFI */



#endif /* __ASSEMBLER__ */

arch/riscv/kernel/entry.S

+4 −0
Original line number Diff line number Diff line
@@ -174,6 +174,10 @@ SYM_CODE_START(handle_exception) 
	 * or vector in kernel space.

	 */

	li t0, SR_SUM | SR_FS_VS

#ifdef CONFIG_64BIT

	li t1, SR_ELP

	or t0, t0, t1

#endif



	REG_L s0, TASK_TI_USER_SP(tp)

	csrrc s1, CSR_STATUS, t0

arch/riscv/kernel/process.c

+5 −0
Original line number Diff line number Diff line
@@ -163,6 +163,11 @@ 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);

	/*

	 * disable indirect branch tracking on exec.

	 * libc will enable it later via prctl.

	 */

	set_indir_lp_status(current, false);



#ifdef CONFIG_64BIT

	regs->status &= ~SR_UXL;

arch/riscv/kernel/usercfi.c

+79 −0
Original line number Diff line number Diff line
@@ -72,6 +72,35 @@ void set_shstk_lock(struct task_struct *task) 
	task->thread_info.user_cfi_state.ubcfi_locked = 1;

}



bool is_indir_lp_enabled(struct task_struct *task)

{

	return task->thread_info.user_cfi_state.ufcfi_en;

}



bool is_indir_lp_locked(struct task_struct *task)

{

	return task->thread_info.user_cfi_state.ufcfi_locked;

}



void set_indir_lp_status(struct task_struct *task, bool enable)

{

	if (!cpu_supports_indirect_br_lp_instr())

		return;



	task->thread_info.user_cfi_state.ufcfi_en = enable ? 1 : 0;



	if (enable)

		task->thread.envcfg |= ENVCFG_LPE;

	else

		task->thread.envcfg &= ~ENVCFG_LPE;



	csr_write(CSR_ENVCFG, task->thread.envcfg);

}



void set_indir_lp_lock(struct task_struct *task)

{

	task->thread_info.user_cfi_state.ufcfi_locked = 1;

}

/*

 * If size is 0, then to be compatible with regular stack we want it to be as big as

 * regular stack. Else PAGE_ALIGN it and return back
@@ -368,3 +397,53 @@ int arch_lock_shadow_stack_status(struct task_struct *task, 


	return 0;

}



int arch_get_indir_br_lp_status(struct task_struct *t, unsigned long __user *status)

{

	unsigned long fcfi_status = 0;



	if (!cpu_supports_indirect_br_lp_instr())

		return -EINVAL;



	/* indirect branch tracking is enabled on the task or not */

	fcfi_status |= (is_indir_lp_enabled(t) ? PR_INDIR_BR_LP_ENABLE : 0);



	return copy_to_user(status, &fcfi_status, sizeof(fcfi_status)) ? -EFAULT : 0;

}



int arch_set_indir_br_lp_status(struct task_struct *t, unsigned long status)

{

	bool enable_indir_lp = false;



	if (!cpu_supports_indirect_br_lp_instr())

		return -EINVAL;



	/* indirect branch tracking is locked and further can't be modified by user */

	if (is_indir_lp_locked(t))

		return -EINVAL;



	/* Reject unknown flags */

	if (status & ~PR_INDIR_BR_LP_ENABLE)

		return -EINVAL;



	enable_indir_lp = (status & PR_INDIR_BR_LP_ENABLE);

	set_indir_lp_status(t, enable_indir_lp);



	return 0;

}



int arch_lock_indir_br_lp_status(struct task_struct *task,

				 unsigned long arg)

{

	/*

	 * If indirect branch tracking is not supported or not enabled on task,

	 * nothing to lock here

	 */

	if (!cpu_supports_indirect_br_lp_instr() ||

	    !is_indir_lp_enabled(task) || arg != 0)

		return -EINVAL;



	set_indir_lp_lock(task);



	return 0;

}