Uprobes need more advanced read, push, and pop userspace GCS
functionality. Implement those features using the existing gcsstr()
and copy_from_user().

Its important to note that GCS pages can be read by normal
instructions, but the hardware validates that pages used by GCS
specific operations, have a GCS privilege set. We aren't validating this
in load_user_gcs because it requires stabilizing the VMA over the read
which may fault.

Signed-off-by: Jeremy Linton <redacted>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
---
  arch/arm64/include/asm/gcs.h | 54 ++++++++++++++++++++++++++++++++++++
  1 file changed, 54 insertions(+)

diff --git a/arch/arm64/include/asm/gcs.h b/arch/arm64/include/asm/gcs.h
index e3b360c9dba4..bd9ff1dedcd9 100644
--- a/arch/arm64/include/asm/gcs.h
+++ b/arch/arm64/include/asm/gcs.h

@@ -116,6 +116,47 @@ static inline void put_user_gcs(unsigned long val, unsigned long __user *addr,
  	uaccess_ttbr0_disable();
  }
  
+static inline void push_user_gcs(unsigned long val, int *err)
+{
+	u64 gcspr = read_sysreg_s(SYS_GCSPR_EL0);
+
+	gcspr -= sizeof(u64);
+	put_user_gcs(val, (unsigned long __user *)gcspr, err);
+	if (!*err)
+		write_sysreg_s(gcspr, SYS_GCSPR_EL0);
+}
+
+/*
+ * Unlike put/push_user_gcs() above, get/pop_user_gsc() doesn't
+ * validate the GCS permission is set on the page being read.  This
+ * differs from how the hardware works when it consumes data stored at
+ * GCSPR. Callers should assure this is acceptable.
+ */
+static inline u64 get_user_gcs(unsigned long __user *addr, int *err)
+{
+	unsigned long ret;
+	u64 load = 0;
+
+	/* Ensure previous GCS operation are visible before we read the page */
+	gcsb_dsync();
+	ret = copy_from_user(&load, addr, sizeof(load));
+	if (ret != 0)
+		*err = ret;
+	return load;
+}
+
+static inline u64 pop_user_gcs(int *err)
+{
+	u64 gcspr = read_sysreg_s(SYS_GCSPR_EL0);
+	u64 read_val;
+
+	read_val = get_user_gcs((unsigned long __user *)gcspr, err);
+	if (!*err)
+		write_sysreg_s(gcspr + sizeof(u64), SYS_GCSPR_EL0);
+
+	return read_val;
+}
+
  #else
  
  static inline bool task_gcs_el0_enabled(struct task_struct *task)

@@ -126,6 +167,10 @@ static inline bool task_gcs_el0_enabled(struct task_struct *task)
  static inline void gcs_set_el0_mode(struct task_struct *task) { }
  static inline void gcs_free(struct task_struct *task) { }
  static inline void gcs_preserve_current_state(void) { }
+static inline void put_user_gcs(unsigned long val, unsigned long __user *addr,
+				int *err) { }
+static inline void push_user_gcs(unsigned long val, int *err) { }
+
  static inline unsigned long gcs_alloc_thread_stack(struct task_struct *tsk,
  						   const struct kernel_clone_args *args)
  {

@@ -136,6 +181,15 @@ static inline int gcs_check_locked(struct task_struct *task,
  {
  	return 0;
  }
+static inline u64 load_user_gcs(unsigned long __user *addr, int *err)
+{
+	*err = -EFAULT;
+	return 0;
+}