[kernel-hardening] [PATCH v4 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-20170322
---
 arch/arm64/Kconfig        |  1 +
 arch/arm64/kernel/entry.S | 25 +++++++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index f2b0b528037d..0e86d87259f4 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..685b43771ac9 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -744,6 +744,10 @@ ENDPROC(cpu_switch_to)
 ret_fast_syscall:
 	disable_irq				// disable interrupts
 	str	x0, [sp, #S_X0]			// returned x0
+	ldr	x2, [tsk, #TSK_TI_ADDR_LIMIT]	// check addr limit change
+	mov	x1, #TASK_SIZE_64
+	cmp	x2, x1
+	b.ne	addr_limit_fail
 	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 +775,11 @@ work_pending:
  */
 ret_to_user:
 	disable_irq				// disable interrupts
+	ldr	x2, [tsk, #TSK_TI_ADDR_LIMIT]	// check addr limit change
+	mov	x1, #TASK_SIZE_64
+	cmp	x2, x1
+	b.ne	addr_limit_fail
+
 	ldr	x1, [tsk, #TSK_TI_FLAGS]
 	and	x2, x1, #_TIF_WORK_MASK
 	cbnz	x2, work_pending
@@ -779,6 +788,22 @@ finish_ret_to_user:
 	kernel_exit 0
 ENDPROC(ret_to_user)
 
+addr_limit_fail:
+#ifdef CONFIG_BUG_ON_DATA_CORRUPTION
+	stp	x0, lr, [sp,#-16]!
+	bl	verify_pre_usermode_state
+	ldp	x0, lr, [sp],#16
+#else
+	/*
+	 * Similar to set_fs(USER_DS) in verify_pre_usermode_state without a
+	 * warning.
+	 */
+	mov	x2, #TASK_SIZE_64
+	str	x2, [tsk, #TSK_TI_ADDR_LIMIT]
+	ALTERNATIVE(nop, SET_PSTATE_UAO(0), ARM64_HAS_UAO, CONFIG_ARM64_UAO)
+#endif
+	ret	lr
+
 /*
  * This is how we return from a fork.
  */
-- 
2.12.1.500.gab5fba24ee-goog