MIPS: uaccess: Take EVA into account in [__]clear_user

__clear_user() (and clear_user() which uses it), always access the user
mode address space, which results in EVA store instructions when EVA is
enabled even if the current user address limit is KERNEL_DS.

Fix this by adding a new symbol __bzero_kernel for the normal kernel
address space bzero in EVA mode, and call that from __clear_user() if
eva_kernel_access().
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Markos Chandras <markos.chandras@imgtec.com>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: Leonid Yegoshin <leonid.yegoshin@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/10844/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/uaccess.h

@@ -1235,6 +1235,17 @@ __clear_user(void __user *addr, __kernel_size_t size)
 {
 	__kernel_size_t res;
 
+	if (eva_kernel_access()) {
+		__asm__ __volatile__(
+			"move\t$4, %1\n\t"
+			"move\t$5, $0\n\t"
+			"move\t$6, %2\n\t"
+			__MODULE_JAL(__bzero_kernel)
+			"move\t%0, $6"
+			: "=r" (res)
+			: "r" (addr), "r" (size)
+			: "$4", "$5", "$6", __UA_t0, __UA_t1, "$31");
+	} else {
 		might_fault();
 		__asm__ __volatile__(
 			"move\t$4, %1\n\t"
@@ -1245,6 +1256,7 @@ __clear_user(void __user *addr, __kernel_size_t size)
 			: "=r" (res)
 			: "r" (addr), "r" (size)
 			: "$4", "$5", "$6", __UA_t0, __UA_t1, "$31");
+	}
 
 	return res;
 }

arch/mips/kernel/mips_ksyms.c

@@ -17,6 +17,7 @@
 #include <asm/fpu.h>
 #include <asm/msa.h>
 
+extern void *__bzero_kernel(void *__s, size_t __count);
 extern void *__bzero(void *__s, size_t __count);
 extern long __strncpy_from_kernel_nocheck_asm(char *__to,
 					      const char *__from, long __len);
@@ -64,6 +65,7 @@ EXPORT_SYMBOL(__copy_from_user_eva);
 EXPORT_SYMBOL(__copy_in_user_eva);
 EXPORT_SYMBOL(__copy_to_user_eva);
 EXPORT_SYMBOL(__copy_user_inatomic_eva);
+EXPORT_SYMBOL(__bzero_kernel);
 #endif
 EXPORT_SYMBOL(__bzero);
 EXPORT_SYMBOL(__strncpy_from_kernel_nocheck_asm);

arch/mips/lib/memset.S

@@ -283,6 +283,8 @@ LEAF(memset)
 1:
 #ifndef CONFIG_EVA
 FEXPORT(__bzero)
+#else
+FEXPORT(__bzero_kernel)
 #endif
 	__BUILD_BZERO LEGACY_MODE