[PATCH v6 09/38] arm64/gcs: Provide copy_to_user_gcs()

[Mark Brown]

In order for EL1 to write to an EL0 GCS it must use the GCSSTTR instruction
rather than a normal STTR. Provide a copy_to_user_gcs() which does this.
Since it is not possible to store anything other than a 64 bit value the
interface is presented in terms of 64 bit values, using unsigned long
rather than u64 due to sparse.

Signed-off-by: Mark Brown <broonie at kernel.org>
---
 arch/arm64/include/asm/uaccess.h | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 22e10e79f56a..24aa804e95a7 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -445,6 +445,26 @@ static inline int gcssttr(unsigned long __user *addr, unsigned long val)
 	return err;
 }
 
+static inline int copy_to_user_gcs(unsigned long __user *addr,
+				   unsigned long *val,
+				   int count)
+{
+	int ret = -EFAULT;
+	int i;
+
+	if (access_ok((char __user *)addr, count * sizeof(u64))) {
+		uaccess_ttbr0_enable();
+		for (i = 0; i < count; i++) {
+			ret = gcssttr(addr++, *val++);
+			if (ret != 0)
+				break;
+		}
+		uaccess_ttbr0_disable();
+	}
+
+	return ret;
+}
+
 #endif /* CONFIG_ARM64_GCS */
 
 #endif /* __ASM_UACCESS_H */

-- 
2.30.2