On Wed, Mar 25, 2020 at 5:14 PM <glider@xxxxxxxxxx> wrote:
>
> 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.
I think that whenever a patch touches some subsystem, we need to
mention that in the commit title. This patch touches mostly x86, so
"kmsan, x86: ..." or something like that. This will probably make x86
maintainers more involved.
>
> 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
>
