[PATCH v3 19/29] riscv: Implements arch agnostic indirect branch tracking prctls

Deepak Gupta
2024-04-03T23:42:29Z

prctls implemented are:
PR_SET_INDIR_BR_LP_STATUS, PR_GET_INDIR_BR_LP_STATUS and
PR_LOCK_INDIR_BR_LP_STATUS.

Signed-off-by: Deepak Gupta <debug@rivosinc.com>
---
arch/riscv/include/asm/usercfi.h | 22 ++++++++-
arch/riscv/kernel/process.c | 5 +++
arch/riscv/kernel/usercfi.c | 76 ++++++++++++++++++++++++++++++++
3 files changed, 102 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/usercfi.h b/arch/riscv/include/asm/usercfi.h
index a168ae0fa5d8..8accdc8ec164 100644
--- a/arch/riscv/include/asm/usercfi.h
+++ b/arch/riscv/include/asm/usercfi.h
@@ -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 */
@@ -30,6 +32,9 @@ 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);
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);

#define PR_SHADOW_STACK_SUPPORTED_STATUS_MASK (PR_SHADOW_STACK_ENABLE)

@@ -72,6 +77,21 @@ static inline void set_shstk_status(struct task_struct *task, bool enable)

}

+static inline bool is_indir_lp_enabled(struct task_struct *task)
+{
+ return false;
+}
+
+static inline bool is_indir_lp_locked(struct task_struct *task)
+{
+ return false;
+}
+
+static inline void set_indir_lp_status(struct task_struct *task, bool enable)
+{
+
+}
+
#endif /* CONFIG_RISCV_USER_CFI */

#endif /* __ASSEMBLY__ */
diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index 3fb8b23f629b..ebed7589c51a 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -152,6 +152,11 @@ 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;
diff --git a/arch/riscv/kernel/usercfi.c b/arch/riscv/kernel/usercfi.c
index cdedf1f78b3e..13920b9d86f3 100644
--- a/arch/riscv/kernel/usercfi.c
+++ b/arch/riscv/kernel/usercfi.c
@@ -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_info.envcfg |= ENVCFG_LPE;
+ else
+ task->thread_info.envcfg &= ~ENVCFG_LPE;
+
+ csr_write(CSR_ENVCFG, task->thread_info.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
@@ -375,3 +401,53 @@ 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))
+ return -EINVAL;
+
+ set_indir_lp_lock(task);
+
+ return 0;
+}
--
2.43.2