ARM: entry: provide uaccess assembly macro hooks

Provide hooks into the kernel entry and exit paths to permit control
of userspace visibility to the kernel.  The intended use is:

- on entry to kernel from user, uaccess_disable will be called to
  disable userspace visibility
- on exit from kernel to user, uaccess_enable will be called to
  enable userspace visibility
- on entry from a kernel exception, uaccess_save_and_disable will be
  called to save the current userspace visibility setting, and disable
  access
- on exit from a kernel exception, uaccess_restore will be called to
  restore the userspace visibility as it was before the exception
  occurred.

These hooks allows us to keep userspace visibility disabled for the
vast majority of the kernel, except for localised regions where we
want to explicitly access userspace.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 3 insertions, 0 deletions

diff --git a/arch/arm/kernel/entry-header.S b/arch/arm/kernel/entry-header.S
index d47b5161b029..0d22ad206d52 100644
--- a/arch/arm/kernel/entry-header.S
+++ b/arch/arm/kernel/entry-header.S
@@ -215,6 +215,7 @@
 	blne	trace_hardirqs_off
 #endif
 	.endif
+	uaccess_restore
 
 #ifndef CONFIG_THUMB2_KERNEL
 	@ ARM mode SVC restore
@@ -258,6 +259,7 @@
 	@ on the stack remains correct).
 	@
 	.macro  svc_exit_via_fiq
+	uaccess_restore
 #ifndef CONFIG_THUMB2_KERNEL
 	@ ARM mode restore
 	mov	r0, sp
@@ -287,6 +289,7 @@
 
 
 	.macro	restore_user_regs, fast = 0, offset = 0
+	uaccess_enable r1, isb=0
 #ifndef CONFIG_THUMB2_KERNEL
 	@ ARM mode restore
 	mov	r2, sp