@@ -16,7 +16,9 @@ struct kernel_clone_args;
struct cfi_status {
unsigned long ubcfi_en : 1; /* Enable for backward cfi. */
unsigned long ubcfi_locked : 1;
- unsigned long rsvd : ((sizeof(unsigned long) * 8) - 2);
+ unsigned long ufcfi_en : 1; /* Enable for forward cfi. Note that ELP goes in sstatus */
+ unsigned long ufcfi_locked : 1;
+ unsigned long rsvd : ((sizeof(unsigned long) * 8) - 4);
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 */
@@ -33,6 +35,10 @@ 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)
@@ -58,6 +64,14 @@ void set_shstk_status(struct task_struct *task, bool enable);
#define set_shstk_status(task, enable)
+#define is_indir_lp_enabled(task) false
+
+#define is_indir_lp_locked(task) false
+
+#define set_indir_lp_status(task, enable)
+
+#define set_indir_lp_lock(task)
+
#endif /* CONFIG_RISCV_USER_CFI */
#endif /* __ASSEMBLY__ */
@@ -143,7 +143,7 @@ SYM_CODE_START(handle_exception)
* Disable the FPU/Vector to detect illegal usage of floating point
* or vector in kernel space.
*/
- li t0, SR_SUM | SR_FS_VS
+ li t0, SR_SUM | SR_FS_VS | SR_ELP
REG_L s0, TASK_TI_USER_SP(tp)
csrrc s1, CSR_STATUS, t0
@@ -160,6 +160,11 @@ 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;
@@ -69,6 +69,32 @@ 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 ? true : false;
+}
+
+bool is_indir_lp_locked(struct task_struct *task)
+{
+ return task->thread_info.user_cfi_state.ufcfi_locked ? true : false;
+}
+
+void set_indir_lp_status(struct task_struct *task, bool enable)
+{
+ 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
@@ -369,3 +395,53 @@ 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) ? true : false;
+ 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;
+}
@@ -204,4 +204,8 @@ static inline bool cpu_mitigations_auto_nosmt(void)
}
#endif
+int arch_get_indir_br_lp_status(struct task_struct *t, unsigned long __user *status);
+int arch_set_indir_br_lp_status(struct task_struct *t, unsigned long status);
+int arch_lock_indir_br_lp_status(struct task_struct *t, unsigned long status);
+
#endif /* _LINUX_CPU_H_ */
@@ -353,4 +353,31 @@ struct prctl_mm_map {
*/
#define PR_LOCK_SHADOW_STACK_STATUS 76
+/*
+ * Get the current indirect branch tracking configuration for the current
+ * thread, this will be the value configured via PR_SET_INDIR_BR_LP_STATUS.
+ */
+#define PR_GET_INDIR_BR_LP_STATUS 77
+
+/*
+ * Set the indirect branch tracking configuration. PR_INDIR_BR_LP_ENABLE will
+ * enable cpu feature for user thread, to track all indirect branches and ensure
+ * they land on arch defined landing pad instruction.
+ * x86 - If enabled, an indirect branch must land on `ENDBRANCH` instruction.
+ * arch64 - If enabled, an indirect branch must land on `BTI` instruction.
+ * riscv - If enabled, an indirect branch must land on `lpad` instruction.
+ * PR_INDIR_BR_LP_DISABLE will disable feature for user thread and indirect
+ * branches will no more be tracked by cpu to land on arch defined landing pad
+ * instruction.
+ */
+#define PR_SET_INDIR_BR_LP_STATUS 78
+# define PR_INDIR_BR_LP_ENABLE (1UL << 0)
+
+/*
+ * Prevent further changes to the specified indirect branch tracking
+ * configuration. All bits may be locked via this call, including
+ * undefined bits.
+ */
+#define PR_LOCK_INDIR_BR_LP_STATUS 79
+
#endif /* _LINUX_PRCTL_H */
@@ -2336,6 +2336,21 @@ int __weak arch_lock_shadow_stack_status(struct task_struct *t, unsigned long st
return -EINVAL;
}
+int __weak arch_get_indir_br_lp_status(struct task_struct *t, unsigned long __user *status)
+{
+ return -EINVAL;
+}
+
+int __weak arch_set_indir_br_lp_status(struct task_struct *t, unsigned long status)
+{
+ return -EINVAL;
+}
+
+int __weak arch_lock_indir_br_lp_status(struct task_struct *t, unsigned long status)
+{
+ return -EINVAL;
+}
+
#define PR_IO_FLUSHER (PF_MEMALLOC_NOIO | PF_LOCAL_THROTTLE)
#ifdef CONFIG_ANON_VMA_NAME
@@ -2811,6 +2826,21 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
return -EINVAL;
error = arch_lock_shadow_stack_status(me, arg2);
break;
+ case PR_GET_INDIR_BR_LP_STATUS:
+ if (arg3 || arg4 || arg5)
+ return -EINVAL;
+ error = arch_get_indir_br_lp_status(me, (unsigned long __user *)arg2);
+ break;
+ case PR_SET_INDIR_BR_LP_STATUS:
+ if (arg3 || arg4 || arg5)
+ return -EINVAL;
+ error = arch_set_indir_br_lp_status(me, arg2);
+ break;
+ case PR_LOCK_INDIR_BR_LP_STATUS:
+ if (arg3 || arg4 || arg5)
+ return -EINVAL;
+ error = arch_lock_indir_br_lp_status(me, arg2);
+ break;
default:
trace_task_prctl_unknown(option, arg2, arg3, arg4, arg5);
error = -EINVAL;
Three architectures (x86, aarch64, riscv) have support for indirect branch tracking feature in a very similar fashion. On a very high level, indirect branch tracking is a CPU feature where CPU tracks branches which uses memory operand to perform control transfer in program. As part of this tracking on indirect branches, CPU goes in a state where it expects a landing pad instr on target and if not found then CPU raises some fault (architecture dependent) x86 landing pad instr - `ENDBRANCH` aarch64 landing pad instr - `BTI` riscv landing instr - `lpad` Given that three major arches have support for indirect branch tracking, This patch makes `prctl` for indirect branch tracking arch agnostic. To allow userspace to enable this feature for itself, following prtcls are defined: - PR_GET_INDIR_BR_LP_STATUS: Gets current configured status for indirect branch tracking. - PR_SET_INDIR_BR_LP_STATUS: Sets a configuration for indirect branch tracking. Following status options are allowed - PR_INDIR_BR_LP_ENABLE: Enables indirect branch tracking on user thread. - PR_INDIR_BR_LP_DISABLE; Disables indirect branch tracking on user thread. - PR_LOCK_INDIR_BR_LP_STATUS: Locks configured status for indirect branch tracking for user thread. Signed-off-by: Deepak Gupta <debug@rivosinc.com> Reviewed-by: Mark Brown <broonie@kernel.org> --- arch/riscv/include/asm/usercfi.h | 16 ++++++++- arch/riscv/kernel/entry.S | 2 +- arch/riscv/kernel/process.c | 5 +++ arch/riscv/kernel/usercfi.c | 76 ++++++++++++++++++++++++++++++++++++++++ include/linux/cpu.h | 4 +++ include/uapi/linux/prctl.h | 27 ++++++++++++++ kernel/sys.c | 30 ++++++++++++++++ 7 files changed, 158 insertions(+), 2 deletions(-)