Disable the generic pre-usermode check in favor of an optimized
implementation. This patch adds specific checks on user-mode return path
to make it faster and smaller.
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 generic handler is called to stop the kernel on an
explicit check.
Signed-off-by: Thomas Garnier <thgarnie@xxxxxxxxxx>
---
Based on next-20170410
---
arch/arm/Kconfig | 1 +
arch/arm/kernel/entry-common.S | 10 +++++++++-
2 files changed, 10 insertions(+), 1 deletion(-)
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index b0e8c9763e94..af0992debfd2 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/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index eb5cd77bf1d8..c8a8ba5c22ad 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 address_limit_check_failed
/* 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 address_limit_check_failed
asm_trace_hardirqs_on save = 0
/* perform architecture specific actions before user return */
--
2.12.2.715.g7642488e1d-goog
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