Re: [PATCH v4 16/45] kmsan: handle task creation and exiting

[Alexander Potapenko <glider@xxxxxxxxxx>]

On Tue, Jul 12, 2022 at 3:18 PM Marco Elver <elver@xxxxxxxxxx> wrote:
>
> On Fri, 1 Jul 2022 at 16:24, 'Alexander Potapenko' via kasan-dev
> <kasan-dev@xxxxxxxxxxxxxxxx> wrote:
> >
> > Tell KMSAN that a new task is created, so the tool creates a backing
> > metadata structure for that task.
> >
> > Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
> > ---
> > v2:
> >  -- move implementation of kmsan_task_create() and kmsan_task_exit() here
> >
> > v4:
> >  -- change sizeof(type) to sizeof(*ptr)
> >
> > Link: https://linux-review.googlesource.com/id/I0f41c3a1c7d66f7e14aabcfdfc7c69addb945805
> > ---
> >  include/linux/kmsan.h | 17 +++++++++++++++++
> >  kernel/exit.c         |  2 ++
> >  kernel/fork.c         |  2 ++
> >  mm/kmsan/core.c       | 10 ++++++++++
> >  mm/kmsan/hooks.c      | 19 +++++++++++++++++++
> >  mm/kmsan/kmsan.h      |  2 ++
> >  6 files changed, 52 insertions(+)
> >
> > diff --git a/include/linux/kmsan.h b/include/linux/kmsan.h
> > index fd76cea338878..b71e2032222e9 100644
> > --- a/include/linux/kmsan.h
> > +++ b/include/linux/kmsan.h
> > @@ -16,6 +16,7 @@
> >
> >  struct page;
> >  struct kmem_cache;
> > +struct task_struct;
> >
> >  #ifdef CONFIG_KMSAN
> >
> > @@ -42,6 +43,14 @@ struct kmsan_ctx {
> >         bool allow_reporting;
> >  };
> >
> > +void kmsan_task_create(struct task_struct *task);
> > +
> > +/**
> > + * kmsan_task_exit() - Notify KMSAN that a task has exited.
> > + * @task: task about to finish.
> > + */
> > +void kmsan_task_exit(struct task_struct *task);
> > +
> >  /**
> >   * kmsan_alloc_page() - Notify KMSAN about an alloc_pages() call.
> >   * @page:  struct page pointer returned by alloc_pages().
> > @@ -163,6 +172,14 @@ void kmsan_iounmap_page_range(unsigned long start, unsigned long end);
> >
> >  #else
> >
> > +static inline void kmsan_task_create(struct task_struct *task)
> > +{
> > +}
> > +
> > +static inline void kmsan_task_exit(struct task_struct *task)
> > +{
> > +}
> > +
> >  static inline int kmsan_alloc_page(struct page *page, unsigned int order,
> >                                    gfp_t flags)
> >  {
> > diff --git a/kernel/exit.c b/kernel/exit.c
> > index f072959fcab7f..1784b7a741ddd 100644
> > --- a/kernel/exit.c
> > +++ b/kernel/exit.c
> > @@ -60,6 +60,7 @@
> >  #include <linux/writeback.h>
> >  #include <linux/shm.h>
> >  #include <linux/kcov.h>
> > +#include <linux/kmsan.h>
> >  #include <linux/random.h>
> >  #include <linux/rcuwait.h>
> >  #include <linux/compat.h>
> > @@ -741,6 +742,7 @@ void __noreturn do_exit(long code)
> >         WARN_ON(tsk->plug);
> >
> >         kcov_task_exit(tsk);
> > +       kmsan_task_exit(tsk);
> >
> >         coredump_task_exit(tsk);
> >         ptrace_event(PTRACE_EVENT_EXIT, code);
> > diff --git a/kernel/fork.c b/kernel/fork.c
> > index 9d44f2d46c696..6dfca6f00ec82 100644
> > --- a/kernel/fork.c
> > +++ b/kernel/fork.c
> > @@ -37,6 +37,7 @@
> >  #include <linux/fdtable.h>
> >  #include <linux/iocontext.h>
> >  #include <linux/key.h>
> > +#include <linux/kmsan.h>
> >  #include <linux/binfmts.h>
> >  #include <linux/mman.h>
> >  #include <linux/mmu_notifier.h>
> > @@ -1026,6 +1027,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
> >         tsk->worker_private = NULL;
> >
> >         kcov_task_init(tsk);
> > +       kmsan_task_create(tsk);
> >         kmap_local_fork(tsk);
> >
> >  #ifdef CONFIG_FAULT_INJECTION
> > diff --git a/mm/kmsan/core.c b/mm/kmsan/core.c
> > index 16fb8880a9c6d..7eabed03ed10b 100644
> > --- a/mm/kmsan/core.c
> > +++ b/mm/kmsan/core.c
> > @@ -44,6 +44,16 @@ bool kmsan_enabled __read_mostly;
> >   */
> >  DEFINE_PER_CPU(struct kmsan_ctx, kmsan_percpu_ctx);
> >
> > +void kmsan_internal_task_create(struct task_struct *task)
> > +{
> > +       struct kmsan_ctx *ctx = &task->kmsan_ctx;
> > +       struct thread_info *info = current_thread_info();
> > +
> > +       __memset(ctx, 0, sizeof(*ctx));
> > +       ctx->allow_reporting = true;
> > +       kmsan_internal_unpoison_memory(info, sizeof(*info), false);
> > +}
> > +
> >  void kmsan_internal_poison_memory(void *address, size_t size, gfp_t flags,
> >                                   unsigned int poison_flags)
> >  {
> > diff --git a/mm/kmsan/hooks.c b/mm/kmsan/hooks.c
> > index 052e17b7a717d..43a529569053d 100644
> > --- a/mm/kmsan/hooks.c
> > +++ b/mm/kmsan/hooks.c
> > @@ -26,6 +26,25 @@
> >   * skipping effects of functions like memset() inside instrumented code.
> >   */
> >
> > +void kmsan_task_create(struct task_struct *task)
> > +{
> > +       kmsan_enter_runtime();
> > +       kmsan_internal_task_create(task);
> > +       kmsan_leave_runtime();
> > +}
> > +EXPORT_SYMBOL(kmsan_task_create);
> > +
> > +void kmsan_task_exit(struct task_struct *task)
> > +{
> > +       struct kmsan_ctx *ctx = &task->kmsan_ctx;
> > +
> > +       if (!kmsan_enabled || kmsan_in_runtime())
> > +               return;
> > +
> > +       ctx->allow_reporting = false;
> > +}
> > +EXPORT_SYMBOL(kmsan_task_exit);
>
> Why are these EXPORT_SYMBOL? Will they be used from some kernel module?

You're right, most of them will not. Will fix.