[PATCH v3 36/46] objtool: kmsan: list KMSAN API functions as uaccess-safe

[Alexander Potapenko]

KMSAN inserts API function calls in a lot of places (function entries
and exits, local variables, memory accesses), so they may get called
from the uaccess regions as well.

KMSAN API functions are used to update the metadata (shadow/origin pages)
for kernel memory accesses. The metadata pages for kernel pointers are
also located in the kernel memory, so touching them is not a problem.
For userspace pointers, no metadata is allocated.

If an API function is supposed to read or modify the metadata, it does so
for kernel pointers and ignores userspace pointers.
If an API function is supposed to return a pair of metadata pointers for
the instrumentation to use (like all __msan_metadata_ptr_for_TYPE_SIZE()
functions do), it returns the allocated metadata for kernel pointers and
special dummy buffers residing in the kernel memory for userspace
pointers.

As a result, none of KMSAN API functions perform userspace accesses, but
since they might be called from UACCESS regions they use
user_access_save/restore().

Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
---
v3:
 -- updated the patch description

Link: https://linux-review.googlesource.com/id/I242bc9816273fecad4ea3d977393784396bb3c35
---
 tools/objtool/check.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index bd0c2c828940a..44825a96adc7c 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1008,6 +1008,25 @@ static const char *uaccess_safe_builtin[] = {
 	"__sanitizer_cov_trace_cmp4",
 	"__sanitizer_cov_trace_cmp8",
 	"__sanitizer_cov_trace_switch",
+	/* KMSAN */
+	"kmsan_copy_to_user",
+	"kmsan_report",
+	"kmsan_unpoison_memory",
+	"__msan_chain_origin",
+	"__msan_get_context_state",
+	"__msan_instrument_asm_store",
+	"__msan_metadata_ptr_for_load_1",
+	"__msan_metadata_ptr_for_load_2",
+	"__msan_metadata_ptr_for_load_4",
+	"__msan_metadata_ptr_for_load_8",
+	"__msan_metadata_ptr_for_load_n",
+	"__msan_metadata_ptr_for_store_1",
+	"__msan_metadata_ptr_for_store_2",
+	"__msan_metadata_ptr_for_store_4",
+	"__msan_metadata_ptr_for_store_8",
+	"__msan_metadata_ptr_for_store_n",
+	"__msan_poison_alloca",
+	"__msan_warning",
 	/* UBSAN */
 	"ubsan_type_mismatch_common",
 	"__ubsan_handle_type_mismatch",
-- 
2.36.0.rc2.479.g8af0fa9b8e-goog