arm/syscalls: Optimize address limit check

Disable the generic address limit check in favor of an architecture
specific optimized implementation. The generic implementation using
pending work flags did not work well with ARM and alignment faults.

The address limit is checked on each syscall return path to user-mode
path as well as the irq user-mode return function. If the address limit
was changed, a function is called to report data corruption (stopping
the kernel or process based on configuration).

The address limit check has to be done before any pending work because
they can reset the address limit and the process is killed using a
SIGKILL signal. For example the lkdtm address limit check does not work
because the signal to kill the process will reset the user-mode address
limit.

Signed-off-by: Thomas Garnier <thgarnie@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Tested-by: Kees Cook <keescook@chromium.org>
Tested-by: Leonard Crestez <leonard.crestez@nxp.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Pratyush Anand <panand@redhat.com>
Cc: Dave Martin <Dave.Martin@arm.com>
Cc: Will Drewry <wad@chromium.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: David Howells <dhowells@redhat.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-api@vger.kernel.org
Cc: Yonghong Song <yhs@fb.com>
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/1504798247-48833-4-git-send-email-keescook@chromium.org

2 files changed, 18 insertions, 0 deletions

diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index 0b60adf4a5d9..99c908226065 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -12,6 +12,7 @@
 #include <asm/unistd.h>
 #include <asm/ftrace.h>
 #include <asm/unwind.h>
+#include <asm/memory.h>
 #ifdef CONFIG_AEABI
 #include <asm/unistd-oabi.h>
 #endif
@@ -48,10 +49,14 @@ ret_fast_syscall:
  UNWIND(.fnstart        )
  UNWIND(.cantunwind     )
         disable_irq_notrace                     @ disable interrupts
+        ldr     r2, [tsk, #TI_ADDR_LIMIT]
+        cmp     r2, #TASK_SIZE
+        blne    addr_limit_check_failed
         ldr     r1, [tsk, #TI_FLAGS]            @ re-check for syscall tracing
         tst     r1, #_TIF_SYSCALL_WORK | _TIF_WORK_MASK
         bne     fast_work_pending
 
+
         /* perform architecture specific actions before user return */
         arch_ret_to_user r1, lr
 
@@ -74,6 +79,9 @@ ret_fast_syscall:
  UNWIND(.cantunwind     )
         str     r0, [sp, #S_R0 + S_OFF]!        @ save returned r0
         disable_irq_notrace                     @ disable interrupts
+        ldr     r2, [tsk, #TI_ADDR_LIMIT]
+        cmp     r2, #TASK_SIZE
+        blne    addr_limit_check_failed
         ldr     r1, [tsk, #TI_FLAGS]            @ re-check for syscall tracing
         tst     r1, #_TIF_SYSCALL_WORK | _TIF_WORK_MASK
         beq     no_work_pending
@@ -106,6 +114,9 @@ ENTRY(ret_to_user)
 ret_slow_syscall:
         disable_irq_notrace                     @ disable interrupts
 ENTRY(ret_to_user_from_irq)
+        ldr     r2, [tsk, #TI_ADDR_LIMIT]
+        cmp     r2, #TASK_SIZE
+        blne    addr_limit_check_failed
         ldr     r1, [tsk, #TI_FLAGS]
         tst     r1, #_TIF_WORK_MASK
         bne     slow_work_pending
diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
index 5814298ef0b7..b67ae12503f3 100644
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -14,6 +14,7 @@
 #include <linux/uaccess.h>
 #include <linux/tracehook.h>
 #include <linux/uprobes.h>
+#include <linux/syscalls.h>
 
 #include <asm/elf.h>
 #include <asm/cacheflush.h>
@@ -673,3 +674,9 @@ struct page *get_signal_page(void)
 
         return page;
 }
+
+/* Defer to generic check */
+asmlinkage void addr_limit_check_failed(void)
+{
+        addr_limit_user_check();
+}