Some functions are called from handwritten assembly, and therefore don't
have their arguments' metadata fully set up by the instrumentation code.
Mark them with __no_sanitize_memory to avoid false positives from
spreading further.
Certain functions perform task switching, so that the value of |current|
is different as they proceed. Because KMSAN state pointer is only read
once at the beginning of the function, touching it after |current| has
changed may be dangerous.
Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
To: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Marco Elver <elver@xxxxxxxxxx>
Cc: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
---
v3:
- removed TODOs from comments
v4:
- updated the comments, dropped __no_sanitize_memory from idle_cpu(),
sched_init(), profile_tick()
- split away the uprobes part as requested by Andrey Konovalov
Change-Id: I684d23dac5a22eb0a4cea71993cb934302b17cea
---
arch/x86/entry/common.c | 2 ++
arch/x86/include/asm/irq_regs.h | 2 ++
arch/x86/include/asm/syscall_wrapper.h | 2 ++
arch/x86/kernel/apic/apic.c | 3 +++
arch/x86/kernel/dumpstack_64.c | 5 +++++
arch/x86/kernel/process_64.c | 5 +++++
arch/x86/kernel/traps.c | 13 +++++++++++--
kernel/sched/core.c | 22 ++++++++++++++++++++++
8 files changed, 52 insertions(+), 2 deletions(-)
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index ec167d8c41cbd..5c3d0f3a14c37 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -280,6 +280,8 @@ __visible inline void syscall_return_slowpath(struct pt_regs *regs)
}
#ifdef CONFIG_X86_64
+/* Tell KMSAN to not instrument this function and to initialize |regs|. */
+__no_sanitize_memory
__visible void do_syscall_64(unsigned long nr, struct pt_regs *regs)
{
struct thread_info *ti;
diff --git a/arch/x86/include/asm/irq_regs.h b/arch/x86/include/asm/irq_regs.h
index 187ce59aea28e..a6fc1641e2861 100644
--- a/arch/x86/include/asm/irq_regs.h
+++ b/arch/x86/include/asm/irq_regs.h
@@ -14,6 +14,8 @@
DECLARE_PER_CPU(struct pt_regs *, irq_regs);
+/* Tell KMSAN to return an initialized struct pt_regs. */
+__no_sanitize_memory
static inline struct pt_regs *get_irq_regs(void)
{
return __this_cpu_read(irq_regs);
diff --git a/arch/x86/include/asm/syscall_wrapper.h b/arch/x86/include/asm/syscall_wrapper.h
index e2389ce9bf58a..098b1a8d6bc41 100644
--- a/arch/x86/include/asm/syscall_wrapper.h
+++ b/arch/x86/include/asm/syscall_wrapper.h
@@ -196,6 +196,8 @@ struct pt_regs;
ALLOW_ERROR_INJECTION(__x64_sys##name, ERRNO); \
static long __se_sys##name(__MAP(x,__SC_LONG,__VA_ARGS__)); \
static inline long __do_sys##name(__MAP(x,__SC_DECL,__VA_ARGS__));\
+ /* Tell KMSAN to initialize |regs|. */ \
+ __no_sanitize_memory \
asmlinkage long __x64_sys##name(const struct pt_regs *regs) \
{ \
return __se_sys##name(SC_X86_64_REGS_TO_ARGS(x,__VA_ARGS__));\
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 5f973fed3c9ff..1f0250f14e462 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1127,6 +1127,9 @@ static void local_apic_timer_interrupt(void)
* [ if a single-CPU system runs an SMP kernel then we call the local
* interrupt as well. Thus we cannot inline the local irq ... ]
*/
+
+/* Tell KMSAN to initialize |regs|. */
+__no_sanitize_memory
__visible void __irq_entry smp_apic_timer_interrupt(struct pt_regs *regs)
{
struct pt_regs *old_regs = set_irq_regs(regs);
diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
index 87b97897a8810..3d1691f81cada 100644
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -150,6 +150,11 @@ static bool in_irq_stack(unsigned long *stack, struct stack_info *info)
return true;
}
+/*
+ * This function may touch stale uninitialized values on stack. Do not
+ * instrument it with KMSAN to avoid false positives.
+ */
+__no_sanitize_memory
int get_stack_info(unsigned long *stack, struct task_struct *task,
struct stack_info *info, unsigned long *visit_mask)
{
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index ffd497804dbc3..5e8c6767e9916 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -424,6 +424,11 @@ void compat_start_thread(struct pt_regs *regs, u32 new_ip, u32 new_sp)
* Kprobes not supported here. Set the probe on schedule instead.
* Function graph tracer not supported too.
*/
+/*
+ * Avoid touching KMSAN state or reporting anything here, as __switch_to() does
+ * weird things with tasks.
+ */
+__no_sanitize_memory
__visible __notrace_funcgraph struct task_struct *
__switch_to(struct task_struct *prev_p, struct task_struct *next_p)
{
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index d54cffdc7cac2..917268aee054e 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -638,7 +638,11 @@ NOKPROBE_SYMBOL(do_int3);
* Help handler running on a per-cpu (IST or entry trampoline) stack
* to switch to the normal thread stack if the interrupted code was in
* user mode. The actual stack switch is done in entry_64.S
+ *
*/
+
+/* This function switches the registers - don't instrument it with KMSAN. */
+__no_sanitize_memory
asmlinkage __visible notrace struct pt_regs *sync_regs(struct pt_regs *eregs)
{
struct pt_regs *regs = (struct pt_regs *)this_cpu_read(cpu_current_top_of_stack) - 1;
@@ -654,6 +658,11 @@ struct bad_iret_stack {
};
asmlinkage __visible notrace
+/*
+ * Dark magic happening here, let's not instrument this function.
+ * Also avoid copying any metadata by using raw __memmove().
+ */
+__no_sanitize_memory
struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s)
{
/*
@@ -668,10 +677,10 @@ struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s)
(struct bad_iret_stack *)this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;
/* Copy the IRET target to the new stack. */
- memmove(&new_stack->regs.ip, (void *)s->regs.sp, 5*8);
+ __memmove(&new_stack->regs.ip, (void *)s->regs.sp, 5*8);
/* Copy the remainder of the stack from the current stack. */
- memmove(new_stack, s, offsetof(struct bad_iret_stack, regs.ip));
+ __memmove(new_stack, s, offsetof(struct bad_iret_stack, regs.ip));
BUG_ON(!user_mode(&new_stack->regs));
return new_stack;
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 1a5937936ac75..bb1b659c12f6a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -471,6 +471,11 @@ void wake_q_add_safe(struct wake_q_head *head, struct task_struct *task)
put_task_struct(task);
}
+/*
+ * Context switch here may lead to KMSAN task state corruption. Disable KMSAN
+ * instrumentation.
+ */
+__no_sanitize_memory
void wake_up_q(struct wake_q_head *head)
{
struct wake_q_node *node = head->first;
@@ -3217,6 +3222,12 @@ prepare_task_switch(struct rq *rq, struct task_struct *prev,
* past. prev == current is still correct but we need to recalculate this_rq
* because prev may have moved to another CPU.
*/
+
+/*
+ * Context switch here may lead to KMSAN task state corruption. Disable KMSAN
+ * instrumentation.
+ */
+__no_sanitize_memory
static struct rq *finish_task_switch(struct task_struct *prev)
__releases(rq->lock)
{
@@ -4052,6 +4063,12 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
*
* WARNING: must be called with preemption disabled!
*/
+
+/*
+ * Context switch here may lead to KMSAN task state corruption. Disable KMSAN
+ * instrumentation.
+ */
+__no_sanitize_memory
static void __sched notrace __schedule(bool preempt)
{
struct task_struct *prev, *next;
@@ -6789,6 +6806,11 @@ static inline int preempt_count_equals(int preempt_offset)
return (nested == preempt_offset);
}
+/*
+ * This function might be called from code that is not instrumented with KMSAN.
+ * Nevertheless, treat its arguments as initialized.
+ */
+__no_sanitize_memory
void __might_sleep(const char *file, int line, int preempt_offset)
{
/*
--
2.25.1.696.g5e7596f4ac-goog
