[RFC PATCH 6/6] riscv: ptrace: Add hw breakpoint support

[Jesse Taube <jesse@rivosinc.com>]

Add ability to setup hw breakpoints to ptrace. Call defines a new
structure of (ulong[3]){bp_addr, bp_len, bp_type} with
bp_type being one of HW_BREAKPOINT_LEN_X and
bp_len being one of HW_BREAKPOINT_X with a value of
zero dissabling the breakpoint.

Signed-off-by: Jesse Taube <jesse@rivosinc.com>
---
 arch/riscv/include/asm/processor.h   |  4 ++
 arch/riscv/include/uapi/asm/ptrace.h |  3 +-
 arch/riscv/kernel/hw_breakpoint.c    | 14 ++++-
 arch/riscv/kernel/process.c          |  4 ++
 arch/riscv/kernel/ptrace.c           | 93 ++++++++++++++++++++++++++++
 5 files changed, 116 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
index 5f56eb9d114a..488d956a951f 100644
--- a/arch/riscv/include/asm/processor.h
+++ b/arch/riscv/include/asm/processor.h
@@ -12,6 +12,7 @@
 
 #include <vdso/processor.h>
 
+#include <asm/hw_breakpoint.h>
 #include <asm/ptrace.h>
 
 #define arch_get_mmap_end(addr, len, flags)			\
@@ -108,6 +109,9 @@ struct thread_struct {
 	struct __riscv_v_ext_state vstate;
 	unsigned long align_ctl;
 	struct __riscv_v_ext_state kernel_vstate;
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+	struct perf_event *ptrace_bps[RV_MAX_TRIGGERS];
+#endif
 #ifdef CONFIG_SMP
 	/* Flush the icache on migration */
 	bool force_icache_flush;
diff --git a/arch/riscv/include/uapi/asm/ptrace.h b/arch/riscv/include/uapi/asm/ptrace.h
index a38268b19c3d..a7998ed41913 100644
--- a/arch/riscv/include/uapi/asm/ptrace.h
+++ b/arch/riscv/include/uapi/asm/ptrace.h
@@ -14,7 +14,8 @@
 
 #define PTRACE_GETFDPIC_EXEC	0
 #define PTRACE_GETFDPIC_INTERP	1
-
+#define PTRACE_GETHBPREGS	2
+#define PTRACE_SETHBPREGS	3
 /*
  * User-mode register state for core dumps, ptrace, sigcontext
  *
diff --git a/arch/riscv/kernel/hw_breakpoint.c b/arch/riscv/kernel/hw_breakpoint.c
index 437fd82b9590..c58145464539 100644
--- a/arch/riscv/kernel/hw_breakpoint.c
+++ b/arch/riscv/kernel/hw_breakpoint.c
@@ -633,7 +633,19 @@ void arch_uninstall_hw_breakpoint(struct perf_event *event)
 		pr_warn("%s: Failed to uninstall trigger %d. error: %ld\n", __func__, i, ret.error);
 }
 
-void flush_ptrace_hw_breakpoint(struct task_struct *tsk) { }
+/*
+ * Release the user breakpoints used by ptrace
+ */
+void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
+{
+	int i;
+	struct thread_struct *t = &tsk->thread;
+
+	for (i = 0; i < dbtr_total_num; i++) {
+		unregister_hw_breakpoint(t->ptrace_bps[i]);
+		t->ptrace_bps[i] = NULL;
+	}
+}
 
 void hw_breakpoint_pmu_read(struct perf_event *bp) { }
 
diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
index 15d8f75902f8..9cf07ecfb523 100644
--- a/arch/riscv/kernel/process.c
+++ b/arch/riscv/kernel/process.c
@@ -9,6 +9,7 @@
 
 #include <linux/bitfield.h>
 #include <linux/cpu.h>
+#include <linux/hw_breakpoint.h>
 #include <linux/kernel.h>
 #include <linux/sched.h>
 #include <linux/sched/debug.h>
@@ -164,6 +165,7 @@ void start_thread(struct pt_regs *regs, unsigned long pc,
 
 void flush_thread(void)
 {
+	flush_ptrace_hw_breakpoint(current);
 #ifdef CONFIG_FPU
 	/*
 	 * Reset FPU state and context
@@ -218,6 +220,8 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 		set_bit(MM_CONTEXT_LOCK_PMLEN, &p->mm->context.flags);
 
 	memset(&p->thread.s, 0, sizeof(p->thread.s));
+	if (IS_ENABLED(CONFIG_HAVE_HW_BREAKPOINT))
+		memset(p->thread.ptrace_bps, 0, sizeof(p->thread.ptrace_bps));
 
 	/* p->thread holds context to be restored by __switch_to() */
 	if (unlikely(args->fn)) {
diff --git a/arch/riscv/kernel/ptrace.c b/arch/riscv/kernel/ptrace.c
index ea67e9fb7a58..b78cfb0f1c0e 100644
--- a/arch/riscv/kernel/ptrace.c
+++ b/arch/riscv/kernel/ptrace.c
@@ -9,11 +9,13 @@
 
 #include <asm/vector.h>
 #include <asm/ptrace.h>
+#include <asm/hw_breakpoint.h>
 #include <asm/syscall.h>
 #include <asm/thread_info.h>
 #include <asm/switch_to.h>
 #include <linux/audit.h>
 #include <linux/compat.h>
+#include <linux/hw_breakpoint.h>
 #include <linux/ptrace.h>
 #include <linux/elf.h>
 #include <linux/regset.h>
@@ -336,12 +338,103 @@ void ptrace_disable(struct task_struct *child)
 {
 }
 
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+static void ptrace_hbptriggered(struct perf_event *bp,
+				struct perf_sample_data *data,
+				struct pt_regs *regs)
+{
+	struct arch_hw_breakpoint *bkpt = counter_arch_bp(bp);
+	int num = 0;
+
+	force_sig_ptrace_errno_trap(num, (void __user *)bkpt->address);
+}
+
+/*
+ * idx selects the breakpoint index.
+ * Both PTRACE_GETHBPREGS and PTRACE_SETHBPREGS transfer three 32-bit words:
+ * address (0), length (1), type (2).
+ * Instruction breakpoint length is one of HW_BREAKPOINT_LEN_X or 0. 0 will
+ * disable the breakpoint.
+ * Instruction breakpoint type is one of HW_BREAKPOINT_X.
+ */
+
+static long ptrace_gethbpregs(struct task_struct *child, unsigned long idx,
+			      unsigned long __user *datap)
+{
+	struct perf_event *bp;
+	unsigned long user_data[3] = {0};
+
+	if (idx >= RV_MAX_TRIGGERS)
+		return -EINVAL;
+
+	bp = child->thread.ptrace_bps[idx];
+
+	if (!IS_ERR_OR_NULL(bp)) {
+		user_data[0] = bp->attr.bp_addr;
+		user_data[1] = bp->attr.disabled ? 0 : bp->attr.bp_len;
+		user_data[2] = bp->attr.bp_type;
+	}
+
+	if (copy_to_user(datap, user_data, sizeof(user_data)))
+		return -EFAULT;
+
+	return 0;
+}
+
+static long ptrace_sethbpregs(struct task_struct *child, unsigned long idx,
+			      unsigned long __user *datap)
+{
+	struct perf_event *bp;
+	struct perf_event_attr attr;
+	unsigned long user_data[3];
+
+	if (idx >= RV_MAX_TRIGGERS)
+		return -EINVAL;
+
+	if (copy_from_user(user_data, datap, sizeof(user_data)))
+		return -EFAULT;
+
+	bp = child->thread.ptrace_bps[idx];
+	if (IS_ERR_OR_NULL(bp))
+		attr = bp->attr;
+	else
+		ptrace_breakpoint_init(&attr);
+
+	attr.bp_addr = user_data[0];
+	attr.bp_len = user_data[1];
+	attr.bp_type = user_data[2];
+	attr.disabled = !attr.bp_len;
+
+	if (IS_ERR_OR_NULL(bp)) {
+		bp = register_user_hw_breakpoint(&attr, ptrace_hbptriggered, NULL,
+					   child);
+		if (IS_ERR(bp))
+			return PTR_ERR(bp);
+
+		child->thread.ptrace_bps[idx] = bp;
+		return 0;
+	} else {
+		return modify_user_hw_breakpoint(bp, &attr);
+	}
+}
+#endif
+
 long arch_ptrace(struct task_struct *child, long request,
 		 unsigned long addr, unsigned long data)
 {
 	long ret = -EIO;
+	unsigned long __user *datap = (unsigned long __user *) data;
 
 	switch (request) {
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+	case PTRACE_GETHBPREGS:
+		ret = ptrace_gethbpregs(child, addr, datap);
+		break;
+
+	case PTRACE_SETHBPREGS:
+		ret = ptrace_sethbpregs(child, addr, datap);
+		break;
+#endif
 	default:
 		ret = ptrace_request(child, request, addr, data);
 		break;
-- 
2.43.0