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

Alexander Potapenko
2022-08-02T15:49:30Z

On Tue, Jul 12, 2022 at 3:18 PM Marco Elver <elver@google.com> wrote:
>
> On Fri, 1 Jul 2022 at 16:24, 'Alexander Potapenko' via kasan-dev
> <kasan-dev@googlegroups.com> 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@google.com>
> > ---
> > 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.