RISC-V: Implement ptrace regs and stack API

Needed for kprobes support. Copied and adapted from arm64 code.

Guo Ren fixup pt_regs type for linux-5.8-rc1.
Signed-off-by: Patrick Stählin <me@packi.ch>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Reviewed-by: Pekka Enberg <penberg@kernel.org>
Reviewed-by: Zong Li <zong.li@sifive.com>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/Kconfig

@@ -75,6 +75,7 @@ config RISCV
 	select HAVE_PERF_EVENTS
 	select HAVE_PERF_REGS
 	select HAVE_PERF_USER_STACK_DUMP
+	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_STACKPROTECTOR
 	select HAVE_SYSCALL_TRACEPOINTS
 	select IRQ_DOMAIN

arch/riscv/include/asm/ptrace.h

@@ -8,6 +8,7 @@
 
 #include <uapi/asm/ptrace.h>
 #include <asm/csr.h>
+#include <linux/compiler.h>
 
 #ifndef __ASSEMBLY__
 
@@ -60,6 +61,7 @@ struct pt_regs {
 
 #define user_mode(regs) (((regs)->status & SR_PP) == 0)
 
+#define MAX_REG_OFFSET offsetof(struct pt_regs, orig_a0)
 
 /* Helpers for working with the instruction pointer */
 static inline unsigned long instruction_pointer(struct pt_regs *regs)
@@ -85,6 +87,12 @@ static inline void user_stack_pointer_set(struct pt_regs *regs,
 	regs->sp =  val;
 }
 
+/* Valid only for Kernel mode traps. */
+static inline unsigned long kernel_stack_pointer(struct pt_regs *regs)
+{
+	return regs->sp;
+}
+
 /* Helpers for working with the frame pointer */
 static inline unsigned long frame_pointer(struct pt_regs *regs)
 {
@@ -101,6 +109,27 @@ static inline unsigned long regs_return_value(struct pt_regs *regs)
 	return regs->a0;
 }
 
+extern int regs_query_register_offset(const char *name);
+extern unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs,
+					       unsigned int n);
+
+/**
+ * regs_get_register() - get register value from its offset
+ * @regs:	pt_regs from which register value is gotten
+ * @offset:	offset of the register.
+ *
+ * regs_get_register returns the value of a register whose offset from @regs.
+ * The @offset is the offset of the register in struct pt_regs.
+ * If @offset is bigger than MAX_REG_OFFSET, this returns 0.
+ */
+static inline unsigned long regs_get_register(struct pt_regs *regs,
+					      unsigned int offset)
+{
+	if (unlikely(offset > MAX_REG_OFFSET))
+		return 0;
+
+	return *(unsigned long *)((unsigned long)regs + offset);
+}
 #endif /* __ASSEMBLY__ */
 
 #endif /* _ASM_RISCV_PTRACE_H */

arch/riscv/kernel/ptrace.c

@@ -114,6 +114,105 @@ const struct user_regset_view *task_user_regset_view(struct task_struct *task)
 	return &riscv_user_native_view;
 }
 
+struct pt_regs_offset {
+	const char *name;
+	int offset;
+};
+
+#define REG_OFFSET_NAME(r) {.name = #r, .offset = offsetof(struct pt_regs, r)}
+#define REG_OFFSET_END {.name = NULL, .offset = 0}
+
+static const struct pt_regs_offset regoffset_table[] = {
+	REG_OFFSET_NAME(epc),
+	REG_OFFSET_NAME(ra),
+	REG_OFFSET_NAME(sp),
+	REG_OFFSET_NAME(gp),
+	REG_OFFSET_NAME(tp),
+	REG_OFFSET_NAME(t0),
+	REG_OFFSET_NAME(t1),
+	REG_OFFSET_NAME(t2),
+	REG_OFFSET_NAME(s0),
+	REG_OFFSET_NAME(s1),
+	REG_OFFSET_NAME(a0),
+	REG_OFFSET_NAME(a1),
+	REG_OFFSET_NAME(a2),
+	REG_OFFSET_NAME(a3),
+	REG_OFFSET_NAME(a4),
+	REG_OFFSET_NAME(a5),
+	REG_OFFSET_NAME(a6),
+	REG_OFFSET_NAME(a7),
+	REG_OFFSET_NAME(s2),
+	REG_OFFSET_NAME(s3),
+	REG_OFFSET_NAME(s4),
+	REG_OFFSET_NAME(s5),
+	REG_OFFSET_NAME(s6),
+	REG_OFFSET_NAME(s7),
+	REG_OFFSET_NAME(s8),
+	REG_OFFSET_NAME(s9),
+	REG_OFFSET_NAME(s10),
+	REG_OFFSET_NAME(s11),
+	REG_OFFSET_NAME(t3),
+	REG_OFFSET_NAME(t4),
+	REG_OFFSET_NAME(t5),
+	REG_OFFSET_NAME(t6),
+	REG_OFFSET_NAME(status),
+	REG_OFFSET_NAME(badaddr),
+	REG_OFFSET_NAME(cause),
+	REG_OFFSET_NAME(orig_a0),
+	REG_OFFSET_END,
+};
+
+/**
+ * regs_query_register_offset() - query register offset from its name
+ * @name:	the name of a register
+ *
+ * regs_query_register_offset() returns the offset of a register in struct
+ * pt_regs from its name. If the name is invalid, this returns -EINVAL;
+ */
+int regs_query_register_offset(const char *name)
+{
+	const struct pt_regs_offset *roff;
+
+	for (roff = regoffset_table; roff->name != NULL; roff++)
+		if (!strcmp(roff->name, name))
+			return roff->offset;
+	return -EINVAL;
+}
+
+/**
+ * regs_within_kernel_stack() - check the address in the stack
+ * @regs:      pt_regs which contains kernel stack pointer.
+ * @addr:      address which is checked.
+ *
+ * regs_within_kernel_stack() checks @addr is within the kernel stack page(s).
+ * If @addr is within the kernel stack, it returns true. If not, returns false.
+ */
+static bool regs_within_kernel_stack(struct pt_regs *regs, unsigned long addr)
+{
+	return (addr & ~(THREAD_SIZE - 1))  ==
+		(kernel_stack_pointer(regs) & ~(THREAD_SIZE - 1));
+}
+
+/**
+ * regs_get_kernel_stack_nth() - get Nth entry of the stack
+ * @regs:	pt_regs which contains kernel stack pointer.
+ * @n:		stack entry number.
+ *
+ * regs_get_kernel_stack_nth() returns @n th entry of the kernel stack which
+ * is specified by @regs. If the @n th entry is NOT in the kernel stack,
+ * this returns 0.
+ */
+unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs, unsigned int n)
+{
+	unsigned long *addr = (unsigned long *)kernel_stack_pointer(regs);
+
+	addr += n;
+	if (regs_within_kernel_stack(regs, (unsigned long)addr))
+		return *addr;
+	else
+		return 0;
+}
+
 void ptrace_disable(struct task_struct *child)
 {
 	clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);