[PATCH v2 4/4] arm64/syscalls: Specific usage of verify_pre_usermode_state

[Thomas Garnier <thgarnie@google.com>]

Implement specific usage of verify_pre_usermode_state for user-mode
returns for arm64.
---
Based on next-20170308
---
 arch/arm64/Kconfig        |  1 +
 arch/arm64/kernel/entry.S | 15 +++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 896eba61e5ed..da54774838d8 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -24,6 +24,7 @@ config ARM64
 	select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
 	select ARCH_WANT_FRAME_POINTERS
 	select ARCH_HAS_UBSAN_SANITIZE_ALL
+	select ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE
 	select ARM_AMBA
 	select ARM_ARCH_TIMER
 	select ARM_GIC
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 43512d4d7df2..eca392ae63e9 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -737,6 +737,19 @@ ENTRY(cpu_switch_to)
 	ret
 ENDPROC(cpu_switch_to)
 
+#ifdef CONFIG_BUG_ON_DATA_CORRUPTION
+.macro VERIFY_PRE_USERMODE_STATE
+	bl	verify_pre_usermode_state
+.endm
+#else
+/* Similar to set_fs(USER_DS) in verify_pre_usermode_state without a warning. */
+.macro VERIFY_PRE_USERMODE_STATE
+	mov	x1, #TASK_SIZE_64
+	str	x1, [tsk, #TSK_TI_ADDR_LIMIT]
+.endm
+#endif
+
+
 /*
  * This is the fast syscall return path.  We do as little as possible here,
  * and this includes saving x0 back into the kernel stack.
@@ -744,6 +757,7 @@ ENDPROC(cpu_switch_to)
 ret_fast_syscall:
 	disable_irq				// disable interrupts
 	str	x0, [sp, #S_X0]			// returned x0
+	VERIFY_PRE_USERMODE_STATE
 	ldr	x1, [tsk, #TSK_TI_FLAGS]	// re-check for syscall tracing
 	and	x2, x1, #_TIF_SYSCALL_WORK
 	cbnz	x2, ret_fast_syscall_trace
@@ -771,6 +785,7 @@ work_pending:
  */
 ret_to_user:
 	disable_irq				// disable interrupts
+	VERIFY_PRE_USERMODE_STATE
 	ldr	x1, [tsk, #TSK_TI_FLAGS]
 	and	x2, x1, #_TIF_WORK_MASK
 	cbnz	x2, work_pending
-- 
2.12.0.246.ga2ecc84866-goog