[PATCH 7/7] ARM: Move thread_info into task_struct (v7 only)

Keith Packard
2021-09-07T22:00:58Z

This avoids many stack overflow attacks which modified the thread_info
structure by moving that into the task_struct as is done is almost all
other architectures.

This depends on having 'current' stored in the TPIDRPRW register as
that allows us to find thread_info and task_struct once the
thread_info cannot be located using the kernel stack pointer.

Signed-off-by: Keith Packard <keithpac@amazon.com>
---
arch/arm/Kconfig | 1 +
arch/arm/include/asm/assembler.h | 4 ++++
arch/arm/include/asm/thread_info.h | 12 +++++++++++-
arch/arm/kernel/asm-offsets.c | 4 ++++
arch/arm/kernel/entry-armv.S | 4 ++++
arch/arm/vfp/vfpmodule.c | 9 +++++++++
6 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 414fe23fd5ac..5846b4f5444b 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -128,6 +128,7 @@ config ARM
select RTC_LIB
select SET_FS
select SYS_SUPPORTS_APM_EMULATION
+ select THREAD_INFO_IN_TASK if CURRENT_POINTER_IN_TPIDRPRW
# Above selects are sorted alphabetically; please add new ones
# according to that. Thanks.
help
diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
index ea12fe3bb589..b23d2b87184a 100644
--- a/arch/arm/include/asm/assembler.h
+++ b/arch/arm/include/asm/assembler.h
@@ -203,10 +203,14 @@
* Get current thread_info.
*/
.macro get_thread_info, rd
+#ifdef CONFIG_THREAD_INFO_IN_TASK
+ mrc p15, 0, \rd, c13, c0, 4
+#else
ARM( mov \rd, sp, lsr #THREAD_SIZE_ORDER + PAGE_SHIFT )
THUMB( mov \rd, sp )
THUMB( lsr \rd, \rd, #THREAD_SIZE_ORDER + PAGE_SHIFT )
mov \rd, \rd, lsl #THREAD_SIZE_ORDER + PAGE_SHIFT
+#endif
.endm

/*
diff --git a/arch/arm/include/asm/thread_info.h b/arch/arm/include/asm/thread_info.h
index 70d4cbc49ae1..6b67703ca16a 100644
--- a/arch/arm/include/asm/thread_info.h
+++ b/arch/arm/include/asm/thread_info.h
@@ -55,8 +55,10 @@ struct thread_info {
unsigned long flags; /* low level flags */
int preempt_count; /* 0 => preemptable, <0 => bug */
mm_segment_t addr_limit; /* address limit */
+#ifndef CONFIG_THREAD_INFO_IN_TASK
struct task_struct *task; /* main task structure */
__u32 cpu; /* cpu */
+#endif
__u32 cpu_domain; /* cpu domain */
#ifdef CONFIG_STACKPROTECTOR_PER_TASK
unsigned long stack_canary;
@@ -75,14 +77,21 @@ struct thread_info {
#endif
};

+#ifdef CONFIG_THREAD_INFO_IN_TASK
+#define INIT_THREAD_INFO_TASK(tsk)
+#else
+#define INIT_THREAD_INFO_TASK(tsk) .task = &tsk,
+#endif
+
#define INIT_THREAD_INFO(tsk) \
{ \
- .task = &tsk, \
+ INIT_THREAD_INFO_TASK(tsk) \
.flags = 0, \
.preempt_count = INIT_PREEMPT_COUNT, \
.addr_limit = KERNEL_DS, \
}

+#ifndef CONFIG_THREAD_INFO_IN_TASK
/*
* how to get the thread information struct from C
*/
@@ -93,6 +102,7 @@ static inline struct thread_info *current_thread_info(void)
return (struct thread_info *)
(current_stack_pointer & ~(THREAD_SIZE - 1));
}
+#endif

#define thread_saved_pc(tsk) \
((unsigned long)(task_thread_info(tsk)->cpu_context.pc))
diff --git a/arch/arm/kernel/asm-offsets.c b/arch/arm/kernel/asm-offsets.c
index 70993af22d80..2a6745f7423e 100644
--- a/arch/arm/kernel/asm-offsets.c
+++ b/arch/arm/kernel/asm-offsets.c
@@ -44,8 +44,12 @@ int main(void)
DEFINE(TI_FLAGS, offsetof(struct thread_info, flags));
DEFINE(TI_PREEMPT, offsetof(struct thread_info, preempt_count));
DEFINE(TI_ADDR_LIMIT, offsetof(struct thread_info, addr_limit));
+#ifdef CONFIG_THREAD_INFO_IN_TASK
+ DEFINE(TI_CPU, offsetof(struct task_struct, cpu));
+#else
DEFINE(TI_TASK, offsetof(struct thread_info, task));
DEFINE(TI_CPU, offsetof(struct thread_info, cpu));
+#endif
DEFINE(TI_CPU_DOMAIN, offsetof(struct thread_info, cpu_domain));
DEFINE(TI_CPU_SAVE, offsetof(struct thread_info, cpu_context));
DEFINE(TI_USED_CP, offsetof(struct thread_info, used_cp));
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index db3947ee9c3e..5ae687c8c7b8 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -762,9 +762,13 @@ ENTRY(__switch_to)
#endif
switch_tls r1, r4, r5, r3, r7
#ifdef CONFIG_CURRENT_POINTER_IN_TPIDRPRW
+#ifdef CONFIG_THREAD_INFO_IN_TASK
+ set_current r2
+#else
ldr r7, [r2, #TI_TASK]
set_current r7
#endif
+#endif
#if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_SMP)
ldr r7, [r2, #TI_TASK]
ldr r8, =__stack_chk_guard
diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c
index d7a3818da671..84a691da59fa 100644
--- a/arch/arm/vfp/vfpmodule.c
+++ b/arch/arm/vfp/vfpmodule.c
@@ -158,7 +158,12 @@ static void vfp_thread_copy(struct thread_info *thread)
*/
static int vfp_notifier(struct notifier_block *self, unsigned long cmd, void *v)
{
+#ifdef CONFIG_THREAD_INFO_IN_TASK
+ struct task_struct *tsk = v;
+ struct thread_info *thread = &tsk->thread_info;
+#else
struct thread_info *thread = v;
+#endif
u32 fpexc;
#ifdef CONFIG_SMP
unsigned int cpu;
@@ -169,7 +174,11 @@ static int vfp_notifier(struct notifier_block *self, unsigned long cmd, void *v)
fpexc = fmrx(FPEXC);

#ifdef CONFIG_SMP
+#ifdef CONFIG_THREAD_INFO_IN_TASK
+ cpu = tsk->cpu;
+#else
cpu = thread->cpu;
+#endif

/*
* On SMP, if VFP is enabled, save the old state in
--
2.33.0