[kernel-hardening] [PATCH v3 4/4] arm64/syscalls: Specific usage of verify_pre_usermode_state

Thomas Garnier
2017-03-11T00:05:01Z

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 | 25 +++++++++++++++++++++++++
2 files changed, 26 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..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.
*/
--
2.12.0.246.ga2ecc84866-goog