[PATCH RFC v2 19/25] kmsan: disable instrumentation of certain functions

[glider@google.com]

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@google.com>
To: Alexander Potapenko <glider@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Vegard Nossum <vegard.nossum@oracle.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: linux-mm@kvack.org
---

Change-Id: I684d23dac5a22eb0a4cea71993cb934302b17cea
---
 arch/x86/entry/common.c                |  1 +
 arch/x86/include/asm/irq_regs.h        |  1 +
 arch/x86/include/asm/syscall_wrapper.h |  1 +
 arch/x86/kernel/apic/apic.c            |  2 ++
 arch/x86/kernel/dumpstack_64.c         |  1 +
 arch/x86/kernel/process_64.c           |  5 +++++
 arch/x86/kernel/traps.c                | 12 ++++++++++--
 arch/x86/kernel/uprobes.c              |  7 ++++++-
 kernel/profile.c                       |  1 +
 kernel/sched/core.c                    | 11 +++++++++++
 10 files changed, 39 insertions(+), 3 deletions(-)

diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index 3f8e22615812..0dd5b2acb355 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -275,6 +275,7 @@ __visible inline void syscall_return_slowpath(struct pt_regs *regs)
 }
 
 #ifdef CONFIG_X86_64
+__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 187ce59aea28..d65a00bd6f02 100644
--- a/arch/x86/include/asm/irq_regs.h
+++ b/arch/x86/include/asm/irq_regs.h
@@ -14,6 +14,7 @@
 
 DECLARE_PER_CPU(struct pt_regs *, irq_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 e046a405743d..43910ce1b53b 100644
--- a/arch/x86/include/asm/syscall_wrapper.h
+++ b/arch/x86/include/asm/syscall_wrapper.h
@@ -159,6 +159,7 @@
 	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__));\
+	__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 9e2dd2b296cd..43a1edd919ea 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1118,6 +1118,8 @@ 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 ... ]
  */
+/* TODO(glider): |regs| is uninitialized, so is |*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 753b8cfe8b8a..ba883d282a43 100644
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -143,6 +143,7 @@ static bool in_irq_stack(unsigned long *stack, struct stack_info *info)
 	return true;
 }
 
+__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 af64519b2695..27649ee3dbf8 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -500,6 +500,11 @@ 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.
  */
+/*
+ * TODO(glider): __switch_to() does weird things with tasks, don't report
+ * anything here (also avoid touching the KMSAN state).
+ */
+__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 4bb0f8447112..a94282d1f60b 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -618,7 +618,10 @@ 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;
@@ -634,6 +637,11 @@ 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)
 {
 	/*
@@ -648,10 +656,10 @@ 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/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 8cd745ef8c7b..bcd4bf5a909f 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -8,6 +8,7 @@
  *	Jim Keniston
  */
 #include <linux/kernel.h>
+#include <linux/kmsan-checks.h>
 #include <linux/sched.h>
 #include <linux/ptrace.h>
 #include <linux/uprobes.h>
@@ -997,9 +998,13 @@ int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
 int arch_uprobe_exception_notify(struct notifier_block *self, unsigned long val, void *data)
 {
 	struct die_args *args = data;
-	struct pt_regs *regs = args->regs;
+	struct pt_regs *regs;
 	int ret = NOTIFY_DONE;
 
+	kmsan_unpoison_shadow(args, sizeof(*args));
+	regs = args->regs;
+	if (regs)
+		kmsan_unpoison_shadow(regs, sizeof(*regs));
 	/* We are only interested in userspace traps */
 	if (regs && !user_mode(regs))
 		return NOTIFY_DONE;
diff --git a/kernel/profile.c b/kernel/profile.c
index af7c94bf5fa1..835a5b66d1a4 100644
--- a/kernel/profile.c
+++ b/kernel/profile.c
@@ -399,6 +399,7 @@ void profile_hits(int type, void *__pc, unsigned int nr_hits)
 }
 EXPORT_SYMBOL_GPL(profile_hits);
 
+__no_sanitize_memory
 void profile_tick(int type)
 {
 	struct pt_regs *regs = get_irq_regs();
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index dd05a378631a..951d19d217d7 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -475,6 +475,8 @@ void wake_q_add_safe(struct wake_q_head *head, struct task_struct *task)
 		put_task_struct(task);
 }
 
+/* TODO(glider): context switching here. */
+__no_sanitize_memory
 void wake_up_q(struct wake_q_head *head)
 {
 	struct wake_q_node *node = head->first;
@@ -3180,6 +3182,8 @@ 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.
  */
+/* TODO(glider): |current| changes here. */
+__no_sanitize_memory
 static struct rq *finish_task_switch(struct task_struct *prev)
 	__releases(rq->lock)
 {
@@ -3986,6 +3990,8 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
  *
  * WARNING: must be called with preemption disabled!
  */
+/* TODO(glider): |current| changes here. */
+__no_sanitize_memory
 static void __sched notrace __schedule(bool preempt)
 {
 	struct task_struct *prev, *next;
@@ -4605,6 +4611,8 @@ int task_prio(const struct task_struct *p)
  *
  * Return: 1 if the CPU is currently idle. 0 otherwise.
  */
+/* TODO(glider): nothing to report here. */
+__no_sanitize_memory
 int idle_cpu(int cpu)
 {
 	struct rq *rq = cpu_rq(cpu);
@@ -6544,6 +6552,7 @@ static struct kmem_cache *task_group_cache __read_mostly;
 DECLARE_PER_CPU(cpumask_var_t, load_balance_mask);
 DECLARE_PER_CPU(cpumask_var_t, select_idle_mask);
 
+__no_sanitize_memory
 void __init sched_init(void)
 {
 	unsigned long ptr = 0;
@@ -6716,6 +6725,8 @@ static inline int preempt_count_equals(int preempt_offset)
 	return (nested == preempt_offset);
 }
 
+/* TODO(glider): the args are most certainly initialized. */
+__no_sanitize_memory
 void __might_sleep(const char *file, int line, int preempt_offset)
 {
 	/*
-- 
2.24.0.rc0.303.g954a862665-goog