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 <[email protected]>
Signed-off-by: Kees Cook <[email protected]>
Tested-by: Kees Cook <[email protected]>
Tested-by: Leonard Crestez <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Cc: Pratyush Anand <[email protected]>
Cc: Dave Martin <[email protected]>
Cc: Will Drewry <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Russell King <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: David Howells <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Al Viro <[email protected]>
Cc: [email protected]
Cc: Yonghong Song <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]

Author: thgarnie

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

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();
+}