[PATCH v5 11/37] kmsan: Allow disabling KMSAN checks for the current task

[Ilya Leoshkevich <iii@linux.ibm.com>]

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.

Make them reentrant in order to handle memory allocations in interrupt
context. Repurpose the allow_reporting field for this.

Reviewed-by: Alexander Potapenko <glider@google.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 Documentation/dev-tools/kmsan.rst | 11 +++++++++--
 include/linux/kmsan.h             | 24 ++++++++++++++++++++++++
 include/linux/kmsan_types.h       |  2 +-
 mm/kmsan/core.c                   |  1 -
 mm/kmsan/hooks.c                  | 18 +++++++++++++++---
 mm/kmsan/report.c                 |  7 ++++---
 tools/objtool/check.c             |  2 ++
 7 files changed, 55 insertions(+), 10 deletions(-)

diff --git a/Documentation/dev-tools/kmsan.rst b/Documentation/dev-tools/kmsan.rst
index 323eedad53cd..6a48d96c5c85 100644
--- a/Documentation/dev-tools/kmsan.rst
+++ b/Documentation/dev-tools/kmsan.rst
@@ -110,6 +110,13 @@ in the Makefile. Think of this as applying ``__no_sanitize_memory`` to every
 function in the file or directory. Most users won't need KMSAN_SANITIZE, unless
 their code gets broken by KMSAN (e.g. runs at early boot time).
 
+KMSAN checks can also be temporarily disabled for the current task using
+``kmsan_disable_current()`` and ``kmsan_enable_current()`` calls. Each
+``kmsan_enable_current()`` call must be preceded by a
+``kmsan_disable_current()`` call; these call pairs may be nested. One needs to
+be careful with these calls, keeping the regions short and preferring other
+ways to disable instrumentation, where possible.
+
 Support
 =======
 
@@ -338,11 +345,11 @@ 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.h b/include/linux/kmsan.h
index fe6c2212bdb1..23de1b3d6aee 100644
--- a/include/linux/kmsan.h
+++ b/include/linux/kmsan.h
@@ -239,6 +239,22 @@ void kmsan_unpoison_entry_regs(const struct pt_regs *regs);
  */
 void *kmsan_get_metadata(void *addr, bool is_origin);
 
+/*
+ * kmsan_enable_current(): Enable KMSAN for the current task.
+ *
+ * Each kmsan_enable_current() current call must be preceded by a
+ * kmsan_disable_current() call. These call pairs may be nested.
+ */
+void kmsan_enable_current(void);
+
+/*
+ * kmsan_disable_current(): Disable KMSAN for the current task.
+ *
+ * Each kmsan_disable_current() current call must be followed by a
+ * kmsan_enable_current() call. These call pairs may be nested.
+ */
+void kmsan_disable_current(void);
+
 #else
 
 static inline void kmsan_init_shadow(void)
@@ -338,6 +354,14 @@ static inline void kmsan_unpoison_entry_regs(const struct pt_regs *regs)
 {
 }
 
+static inline void kmsan_enable_current(void)
+{
+}
+
+static inline void kmsan_disable_current(void)
+{
+}
+
 #endif
 
 #endif /* _LINUX_KMSAN_H */
diff --git a/include/linux/kmsan_types.h b/include/linux/kmsan_types.h
index 929287981afe..dfc59918b3c0 100644
--- a/include/linux/kmsan_types.h
+++ b/include/linux/kmsan_types.h
@@ -31,7 +31,7 @@ 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 95f859e38c53..81b22220711a 100644
--- a/mm/kmsan/core.c
+++ b/mm/kmsan/core.c
@@ -43,7 +43,6 @@ 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;
 	kmsan_internal_unpoison_memory(info, sizeof(*info), false);
 }
 
diff --git a/mm/kmsan/hooks.c b/mm/kmsan/hooks.c
index b408714f9ba3..267d0afa2e8b 100644
--- a/mm/kmsan/hooks.c
+++ b/mm/kmsan/hooks.c
@@ -39,12 +39,10 @@ void kmsan_task_create(struct task_struct *task)
 
 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;
+	kmsan_disable_current();
 }
 
 void kmsan_slab_alloc(struct kmem_cache *s, void *object, gfp_t flags)
@@ -424,3 +422,17 @@ void kmsan_check_memory(const void *addr, size_t size)
 					   REASON_ANY);
 }
 EXPORT_SYMBOL(kmsan_check_memory);
+
+void kmsan_enable_current(void)
+{
+	KMSAN_WARN_ON(current->kmsan_ctx.depth == 0);
+	current->kmsan_ctx.depth--;
+}
+EXPORT_SYMBOL(kmsan_enable_current);
+
+void kmsan_disable_current(void)
+{
+	current->kmsan_ctx.depth++;
+	KMSAN_WARN_ON(current->kmsan_ctx.depth == 0);
+}
+EXPORT_SYMBOL(kmsan_disable_current);
diff --git a/mm/kmsan/report.c b/mm/kmsan/report.c
index c79d3b0d2d0d..92e73ec61435 100644
--- a/mm/kmsan/report.c
+++ b/mm/kmsan/report.c
@@ -8,6 +8,7 @@
  */
 
 #include <linux/console.h>
+#include <linux/kmsan.h>
 #include <linux/moduleparam.h>
 #include <linux/stackdepot.h>
 #include <linux/stacktrace.h>
@@ -158,12 +159,12 @@ 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;
+	kmsan_disable_current();
 	ua_flags = user_access_save();
 	raw_spin_lock(&kmsan_report_lock);
 	pr_err("=====================================================\n");
@@ -216,5 +217,5 @@ 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;
+	kmsan_enable_current();
 }
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 0a33d9195b7a..01237d167223 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1202,6 +1202,8 @@ static const char *uaccess_safe_builtin[] = {
 	"__sanitizer_cov_trace_switch",
 	/* KMSAN */
 	"kmsan_copy_to_user",
+	"kmsan_disable_current",
+	"kmsan_enable_current",
 	"kmsan_report",
 	"kmsan_unpoison_entry_regs",
 	"kmsan_unpoison_memory",
-- 
2.45.1