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

[Marco Elver <elver@xxxxxxxxxx>]

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?