diff mbox series

[12/32] kmsan: Allow disabling KMSAN checks for the current task

Message ID 20231115203401.2495875-13-iii@linux.ibm.com (mailing list archive)
State Superseded
Headers show
Series kmsan: Enable on s390 | expand

Commit Message

Ilya Leoshkevich Nov. 15, 2023, 8:30 p.m. UTC 
Like for KASAN, it's useful to temporarily disable KMSAN checks around,
e.g., redzone accesses. Introduce kmsan_disable_current() and
kmsan_enable_current(), which are similar to their KASAN counterparts.

Even though it's not strictly necessary, make them reentrant, in order
to match the KASAN behavior. Repurpose the allow_reporting field for
this.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 Documentation/dev-tools/kmsan.rst |  4 ++--
 include/linux/kmsan-checks.h      | 12 ++++++++++++
 include/linux/kmsan_types.h       |  2 +-
 mm/kmsan/core.c                   |  2 +-
 mm/kmsan/hooks.c                  | 14 +++++++++++++-
 mm/kmsan/report.c                 |  6 +++---
 6 files changed, 32 insertions(+), 8 deletions(-)

Comments

Alexander Potapenko Nov. 16, 2023, 8:56 a.m. UTC | #1 
On Wed, Nov 15, 2023 at 9:34 PM Ilya Leoshkevich <iii@linux.ibm.com> wrote:
>
> Like for KASAN, it's useful to temporarily disable KMSAN checks around,
> e.g., redzone accesses.

This example is incorrect, because KMSAN does not have redzones.
You are calling these functions from "mm: slub: Let KMSAN access
metadata", which mentiones redzones in kfree(), but the description is
still somewhat unclear.
Can you provide more insight about what is going on? Maybe we can fix
those accesses instead of disabling KMSAN?
Ilya Leoshkevich Nov. 16, 2023, 9:17 a.m. UTC | #2 
On Thu, 2023-11-16 at 09:56 +0100, Alexander Potapenko wrote:
> On Wed, Nov 15, 2023 at 9:34 PM Ilya Leoshkevich <iii@linux.ibm.com>
> wrote:
> > 
> > Like for KASAN, it's useful to temporarily disable KMSAN checks
> > around,
> > e.g., redzone accesses.
> 
> This example is incorrect, because KMSAN does not have redzones.
> You are calling these functions from "mm: slub: Let KMSAN access
> metadata", which mentiones redzones in kfree(), but the description
> is
> still somewhat unclear.
> Can you provide more insight about what is going on? Maybe we can fix
> those accesses instead of disabling KMSAN?

It's about SLUB redzones, which appear when compiling with
CONFIG_DEBUG_SLAB.

I think that from KMSAN's point of view they should be considered
poisoned, but then the question is what to do with functions that check
them. I noticed that there was special handling for KASAN there
already, so I figured that the best solution would be to do the same
thing for KMSAN.
diff mbox series

Patch

diff --git a/Documentation/dev-tools/kmsan.rst b/Documentation/dev-tools/kmsan.rst
index 323eedad53cd..022a823f5f1b 100644
--- a/Documentation/dev-tools/kmsan.rst
+++ b/Documentation/dev-tools/kmsan.rst
@@ -338,11 +338,11 @@  Per-task KMSAN state
 ~~~~~~~~~~~~~~~~~~~~
 
 Every task_struct has an associated KMSAN task state that holds the KMSAN
-context (see above) and a per-task flag disallowing KMSAN reports::
+context (see above) and a per-task counter disallowing KMSAN reports::
 
   struct kmsan_context {
     ...
-    bool allow_reporting;
+    unsigned int depth;
     struct kmsan_context_state cstate;
     ...
   }
diff --git a/include/linux/kmsan-checks.h b/include/linux/kmsan-checks.h
index 5218973f0ad0..bab2603685f7 100644
--- a/include/linux/kmsan-checks.h
+++ b/include/linux/kmsan-checks.h
@@ -72,6 +72,10 @@  void kmsan_copy_to_user(void __user *to, const void *from, size_t to_copy,
  */
 void kmsan_memmove_metadata(void *dst, const void *src, size_t n);
 
+void kmsan_enable_current(void);
+
+void kmsan_disable_current(void);
+
 #else
 
 static inline void kmsan_poison_memory(const void *address, size_t size,
@@ -92,6 +96,14 @@  static inline void kmsan_memmove_metadata(void *dst, const void *src, size_t n)
 {
 }
 
+static inline void kmsan_enable_current(void)
+{
+}
+
+static inline void kmsan_disable_current(void)
+{
+}
+
 #endif
 
 #endif /* _LINUX_KMSAN_CHECKS_H */
diff --git a/include/linux/kmsan_types.h b/include/linux/kmsan_types.h
index 8bfa6c98176d..27bb146ece95 100644
--- a/include/linux/kmsan_types.h
+++ b/include/linux/kmsan_types.h
@@ -29,7 +29,7 @@  struct kmsan_context_state {
 struct kmsan_ctx {
 	struct kmsan_context_state cstate;
 	int kmsan_in_runtime;
-	bool allow_reporting;
+	unsigned int depth;
 };
 
 #endif /* _LINUX_KMSAN_TYPES_H */
diff --git a/mm/kmsan/core.c b/mm/kmsan/core.c
index c19f47af0424..b8767378cf8a 100644
--- a/mm/kmsan/core.c
+++ b/mm/kmsan/core.c
@@ -43,7 +43,7 @@  void kmsan_internal_task_create(struct task_struct *task)
 	struct thread_info *info = current_thread_info();
 
 	__memset(ctx, 0, sizeof(*ctx));
-	ctx->allow_reporting = true;
+	ctx->depth = 0;
 	kmsan_internal_unpoison_memory(info, sizeof(*info), false);
 }
 
diff --git a/mm/kmsan/hooks.c b/mm/kmsan/hooks.c
index 4d477a0a356c..7b5814412e9f 100644
--- a/mm/kmsan/hooks.c
+++ b/mm/kmsan/hooks.c
@@ -44,7 +44,7 @@  void kmsan_task_exit(struct task_struct *task)
 	if (!kmsan_enabled || kmsan_in_runtime())
 		return;
 
-	ctx->allow_reporting = false;
+	ctx->depth++;
 }
 
 void kmsan_slab_alloc(struct kmem_cache *s, void *object, gfp_t flags)
@@ -434,3 +434,15 @@  void kmsan_check_memory(const void *addr, size_t size)
 					   REASON_ANY);
 }
 EXPORT_SYMBOL(kmsan_check_memory);
+
+void kmsan_enable_current(void)
+{
+	current->kmsan_ctx.depth--;
+}
+EXPORT_SYMBOL(kmsan_enable_current);
+
+void kmsan_disable_current(void)
+{
+	current->kmsan_ctx.depth++;
+}
+EXPORT_SYMBOL(kmsan_disable_current);
diff --git a/mm/kmsan/report.c b/mm/kmsan/report.c
index c79d3b0d2d0d..edcf53ca428e 100644
--- a/mm/kmsan/report.c
+++ b/mm/kmsan/report.c
@@ -158,12 +158,12 @@  void kmsan_report(depot_stack_handle_t origin, void *address, int size,
 
 	if (!kmsan_enabled)
 		return;
-	if (!current->kmsan_ctx.allow_reporting)
+	if (current->kmsan_ctx.depth)
 		return;
 	if (!origin)
 		return;
 
-	current->kmsan_ctx.allow_reporting = false;
+	current->kmsan_ctx.depth++;
 	ua_flags = user_access_save();
 	raw_spin_lock(&kmsan_report_lock);
 	pr_err("=====================================================\n");
@@ -216,5 +216,5 @@  void kmsan_report(depot_stack_handle_t origin, void *address, int size,
 	if (panic_on_kmsan)
 		panic("kmsan.panic set ...\n");
 	user_access_restore(ua_flags);
-	current->kmsan_ctx.allow_reporting = true;
+	current->kmsan_ctx.depth--;
 }