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, 7 insertions, 6 deletions

diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
index 062b58c029ab..4e84d09c9c1b 100644
--- a/arch/arm/include/asm/assembler.h
+++ b/arch/arm/include/asm/assembler.h
@@ -18,6 +18,7 @@
 #endif
 
 #include <asm/ptrace.h>
+#include <asm/domain.h>
 
 /*
  * Endian independent macros for shifting bytes within registers.
@@ -206,12 +207,12 @@
  */
 #ifdef CONFIG_THUMB2_KERNEL
 
-        .macro  usraccoff, instr, reg, ptr, inc, off, cond, abort
+        .macro  usraccoff, instr, reg, ptr, inc, off, cond, abort, t=T()
 9999:
         .if     \inc == 1
-        \instr\cond\()bt \reg, [\ptr, #\off]
+        \instr\cond\()b\()\t\().w \reg, [\ptr, #\off]
         .elseif \inc == 4
-        \instr\cond\()t \reg, [\ptr, #\off]
+        \instr\cond\()\t\().w \reg, [\ptr, #\off]
         .else
         .error  "Unsupported inc macro argument"
         .endif
@@ -246,13 +247,13 @@
 
 #else   /* !CONFIG_THUMB2_KERNEL */
 
-        .macro  usracc, instr, reg, ptr, inc, cond, rept, abort
+        .macro  usracc, instr, reg, ptr, inc, cond, rept, abort, t=T()
         .rept   \rept
 9999:
         .if     \inc == 1
-        \instr\cond\()bt \reg, [\ptr], #\inc
+        \instr\cond\()b\()\t \reg, [\ptr], #\inc
         .elseif \inc == 4
-        \instr\cond\()t \reg, [\ptr], #\inc
+        \instr\cond\()\t \reg, [\ptr], #\inc
         .else
         .error  "Unsupported inc macro argument"
         .endif