ARM: 6384/1: Remove the domain switching on ARMv6k/v7 CPUs

This patch removes the domain switching functionality via the set_fs and
__switch_to functions on cores that have a TLS register.

Currently, the ioremap and vmalloc areas share the same level 1 page
tables and therefore have the same domain (DOMAIN_KERNEL). When the
kernel domain is modified from Client to Manager (via the __set_fs or in
the __switch_to function), the XN (eXecute Never) bit is overridden and
newer CPUs can speculatively prefetch the ioremap'ed memory.

Linux performs the kernel domain switching to allow user-specific
functions (copy_to/from_user, get/put_user etc.) to access kernel
memory. In order for these functions to work with the kernel domain set
to Client, the patch modifies the LDRT/STRT and related instructions to
the LDR/STR ones.

The user pages access rights are also modified for kernel read-only
access rather than read/write so that the copy-on-write mechanism still
works. CPU_USE_DOMAINS gets disabled only if the hardware has a TLS register
(CPU_32v6K is defined) since writing the TLS value to the high vectors page
isn't possible.

The user addresses passed to the kernel are checked by the access_ok()
function so that they do not point to the kernel space.

Tested-by: Anton Vorontsov <cbouatmailru@gmail.com>
Cc: Tony Lindgren <tony@atomide.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 2 insertions, 2 deletions

diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index c09e3573c5de..35f3f20d6731 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -735,7 +735,7 @@ ENTRY(__switch_to)
  THUMB( stmia   ip!, {r4 - sl, fp}         )    @ Store most regs on stack
  THUMB( str     sp, [ip], #4               )
  THUMB( str     lr, [ip], #4               )
-#ifdef CONFIG_MMU
+#ifdef CONFIG_CPU_USE_DOMAINS
         ldr     r6, [r2, #TI_CPU_DOMAIN]
 #endif
         set_tls r3, r4, r5
@@ -744,7 +744,7 @@ ENTRY(__switch_to)
         ldr     r8, =__stack_chk_guard
         ldr     r7, [r7, #TSK_STACK_CANARY]
 #endif
-#ifdef CONFIG_MMU
+#ifdef CONFIG_CPU_USE_DOMAINS
         mcr     p15, 0, r6, c3, c0, 0           @ Set domain register
 #endif
         mov     r5, r0