[kernel-hardening] [PATCH v3 3/4] arm/syscalls: Specific usage of verify_pre_usermode_state

Thomas Garnier
2017-03-11T00:05:00Z

Implement specific usage of verify_pre_usermode_state for user-mode
returns for arm.
---
Based on next-20170308
---
arch/arm/Kconfig | 1 +
arch/arm/include/asm/domain.h | 3 +++
arch/arm/kernel/entry-common.S | 32 +++++++++++++++++++++++++++++++-
3 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 0d4e71b42c77..704fd8f197fa 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -12,6 +12,7 @@ config ARM
select ARCH_HAVE_CUSTOM_GPIO_H
select ARCH_HAS_GCOV_PROFILE_ALL
select ARCH_MIGHT_HAVE_PC_PARPORT
+ select ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE
select ARCH_OPTIONAL_KERNEL_RWX if ARCH_HAS_STRICT_KERNEL_RWX
select ARCH_OPTIONAL_KERNEL_RWX_DEFAULT if CPU_V7
select ARCH_SUPPORTS_ATOMIC_RMW
diff --git a/arch/arm/include/asm/domain.h b/arch/arm/include/asm/domain.h
index 99d9f630d6b6..fd1cd24ca9fe 100644
--- a/arch/arm/include/asm/domain.h
+++ b/arch/arm/include/asm/domain.h
@@ -58,6 +58,9 @@
#define domain_mask(dom) ((3) << (2 * (dom)))
#define domain_val(dom,type) ((type) << (2 * (dom)))

+#define DOMAIN_KERNEL_MASK domain_mask(DOMAIN_KERNEL)
+#define DOMAIN_CLIENT_VALUE domain_val(DOMAIN_KERNEL, DOMAIN_CLIENT)
+
#ifdef CONFIG_CPU_SW_DOMAIN_PAN
#define DACR_INIT \
(domain_val(DOMAIN_USER, DOMAIN_NOACCESS) | \
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index eb5cd77bf1d8..8d9bfe9ff313 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
@@ -27,7 +28,6 @@

#include "entry-header.S"

-
.align 5
#if !(IS_ENABLED(CONFIG_TRACE_IRQFLAGS) || IS_ENABLED(CONFIG_CONTEXT_TRACKING))
/*
@@ -40,9 +40,12 @@ ret_fast_syscall:
UNWIND(.fnstart )
UNWIND(.cantunwind )
disable_irq_notrace @ disable interrupts
+ ldr r2, [tsk, #TI_ADDR_LIMIT]
ldr r1, [tsk, #TI_FLAGS] @ re-check for syscall tracing
tst r1, #_TIF_SYSCALL_WORK | _TIF_WORK_MASK
bne fast_work_pending
+ cmp r2, #TASK_SIZE
+ blne addr_limit_fail

/* perform architecture specific actions before user return */
arch_ret_to_user r1, lr
@@ -66,6 +69,7 @@ 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]
ldr r1, [tsk, #TI_FLAGS] @ re-check for syscall tracing
tst r1, #_TIF_SYSCALL_WORK | _TIF_WORK_MASK
beq no_work_pending
@@ -82,6 +86,7 @@ slow_work_pending:
mov r2, why @ 'syscall'
bl do_work_pending
cmp r0, #0
+ ldreq r2, [tsk, #TI_ADDR_LIMIT]
beq no_work_pending
movlt scno, #(__NR_restart_syscall - __NR_SYSCALL_BASE)
ldmia sp, {r0 - r6} @ have to reload r0 - r6
@@ -99,9 +104,12 @@ ret_slow_syscall:
disable_irq_notrace @ disable interrupts
ENTRY(ret_to_user_from_irq)
ldr r1, [tsk, #TI_FLAGS]
+ ldr r2, [tsk, #TI_ADDR_LIMIT]
tst r1, #_TIF_WORK_MASK
bne slow_work_pending
no_work_pending:
+ cmp r2, #TASK_SIZE
+ blne addr_limit_fail
asm_trace_hardirqs_on save = 0

/* perform architecture specific actions before user return */
@@ -125,6 +133,28 @@ ENTRY(ret_from_fork)
b ret_slow_syscall
ENDPROC(ret_from_fork)

+addr_limit_fail:
+#ifdef CONFIG_BUG_ON_DATA_CORRUPTION
+ stmfd sp!, {r0, lr}
+ bl verify_pre_usermode_state
+ ldmfd sp!, {r0, lr}
+#else
+ /*
+ * Similar to set_fs(USER_DS) in verify_pre_usermode_state without a
+ * warning.
+ */
+ mov r2, #TASK_SIZE
+ str r2, [tsk, #TI_ADDR_LIMIT]
+#ifdef CONFIG_CPU_USE_DOMAINS
+ /* Switch domain like modify_domain(DOMAIN_KERNEL, DOMAIN_CLIENT) */
+ mrc p15, 0, r2, c3, c0, 0 @ Get domain register
+ bic r2, r2, #DOMAIN_KERNEL_MASK @ Clear the domain part
+ orr r2, r2, #DOMAIN_CLIENT_VALUE @ Enforce DOMAIN_CLIENT
+ mcr p15, 0, r2, c3, c0, 0 @ Set domain register
+#endif
+#endif
+ ret lr
+
/*=============================================================================
* SWI handler
*-----------------------------------------------------------------------------
--
2.12.0.246.ga2ecc84866-goog