[PATCH v2 5/6] lib: sbi_sse: fix shared memory double-fetch in sse_write_attrs

[liutong]

sse_write_attrs() reads attribute values from S-mode shared memory in
two passes: first to validate, then to apply. Since the shared memory
remains writable by S-mode between the two reads, the values used for
application may differ from what was validated.

This allows S-mode to bypass validation by modifying shared memory
contents between the two passes, potentially setting unauthorized SSE
event attributes in M-mode.

Fix this by snapshotting the shared memory data into a local buffer
and performing both validation and application against that snapshot.

Fixes: c8cdf01d8f3a ("lib: sbi: Add support for Supervisor Software Events extension")
Signed-off-by: liutong <liutong at iscas.ac.cn>
---

Previously sent as [PATCH v2].
Changes in v2:
- Added Fixes tag
- Consolidated into patch series

 lib/sbi/sbi_sse.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/lib/sbi/sbi_sse.c b/lib/sbi/sbi_sse.c
index 818afb87..94b333c5 100644
--- a/lib/sbi/sbi_sse.c
+++ b/lib/sbi/sbi_sse.c
@@ -1064,25 +1064,27 @@ static int sse_write_attrs(struct sbi_sse_event *e, uint32_t base_attr_id,
 	unsigned long attr = 0, val;
 	uint32_t id, end_id = base_attr_id + attr_count;
 	unsigned long *attrs = (unsigned long *)input_phys;
+	unsigned long local_attrs[SBI_SSE_ATTR_MAX];
 
 	sbi_hart_protection_map_range(input_phys, sizeof(unsigned long) * attr_count);
 
+	copy_attrs(local_attrs, attrs, attr_count);
+
+	sbi_hart_protection_unmap_range(input_phys, sizeof(unsigned long) * attr_count);
+
 	for (id = base_attr_id; id < end_id; id++) {
-		val = attrs[attr++];
+		val = local_attrs[attr++];
 		ret = sse_event_set_attr_check(e, id, val);
 		if (ret)
-			goto out;
+			return ret;
 	}
 
 	attr = 0;
 	for (id = base_attr_id; id < end_id; id++) {
-		val = attrs[attr++];
+		val = local_attrs[attr++];
 		sse_event_set_attr(e, id, val);
 	}
 
-out:
-	sbi_hart_protection_unmap_range(input_phys, sizeof(unsigned long) * attr_count);
-
 	return ret;
 }
 
-- 
2.34.1