[PATCH v2] lib: sbi_dbtr: fix shared memory double-fetch in install_trig

[liutong]

sbi_dbtr_install_trig() reads trigger configuration from S-mode shared
memory in two separate loops: first to validate, then to install. Since
the shared memory remains writable by S-mode between the two reads, the
data used for installation may differ from what was validated.

Fix this by merging validation and installation into a single pass.
Each entry is copied to a local variable before use, so S-mode cannot
modify the data between validation and installation. On validation
failure, all previously installed triggers are rolled back.

Also add a bounds check on trig_count against RV_MAX_TRIGGERS.

Additionally, fix a redundant read in dbtr_trigger_setup() where tdata1
was read from the message pointer a second time instead of using the
value already saved in trig->tdata1.

Signed-off-by: liutong <liutong at iscas.ac.cn>
---
Changes in v2:
 - Replace full-array stack snapshot (local_data[RV_MAX_TRIGGERS], 1KB)
   with per-entry local copy (single struct, 32B) to reduce M-mode
   stack usage
 - Merge validation and installation into a single pass with rollback
   on failure, instead of two separate passes over the snapshot

 lib/sbi/sbi_dbtr.c | 66 ++++++++++++++++++++++------------------------
 1 file changed, 32 insertions(+), 34 deletions(-)

diff --git a/lib/sbi/sbi_dbtr.c b/lib/sbi/sbi_dbtr.c
index 8bcb4312..efd9a7e7 100644
--- a/lib/sbi/sbi_dbtr.c
+++ b/lib/sbi/sbi_dbtr.c
@@ -308,7 +308,7 @@ static void dbtr_trigger_setup(struct sbi_dbtr_trigger *trig,
 	trig->tdata2 = lle_to_cpu(recv->tdata2);
 	trig->tdata3 = lle_to_cpu(recv->tdata3);
 
-	tdata1 = lle_to_cpu(recv->tdata1);
+	tdata1 = trig->tdata1;
 
 	trig->state = 0;
 
@@ -582,12 +582,14 @@ int sbi_dbtr_read_trig(unsigned long smode,
 int sbi_dbtr_install_trig(unsigned long smode,
 			  unsigned long trig_count, unsigned long *out)
 {
+	struct sbi_dbtr_data_msg local;
 	void *shmem_base = NULL;
 	union sbi_dbtr_shmem_entry *entry;
-	struct sbi_dbtr_data_msg *recv;
 	struct sbi_dbtr_id_msg *xmit;
 	unsigned long ctrl;
 	struct sbi_dbtr_trigger *trig;
+	struct sbi_dbtr_trigger *installed[RV_MAX_TRIGGERS];
+	int num_installed = 0;
 	struct sbi_dbtr_hart_triggers_state *hs = NULL;
 
 	hs = dbtr_thishart_state_ptr();
@@ -597,58 +599,54 @@ int sbi_dbtr_install_trig(unsigned long smode,
 	if (sbi_dbtr_shmem_disabled(hs))
 		return SBI_ERR_NO_SHMEM;
 
-	shmem_base = hart_shmem_base(hs);
-	sbi_hart_protection_map_range((unsigned long)shmem_base,
-				      trig_count * sizeof(*entry));
-
-	/* Check requested triggers configuration */
-	for_each_trig_entry(shmem_base, trig_count, typeof(*entry), entry) {
-		recv = (struct sbi_dbtr_data_msg *)(&entry->data);
-		ctrl = recv->tdata1;
-
-		if (!dbtr_trigger_supported(TDATA1_GET_TYPE(ctrl))) {
-			*out = _idx;
-			sbi_hart_protection_unmap_range((unsigned long)shmem_base,
-							trig_count * sizeof(*entry));
-			return SBI_ERR_FAILED;
-		}
-
-		if (!dbtr_trigger_valid(TDATA1_GET_TYPE(ctrl), ctrl)) {
-			*out = _idx;
-			sbi_hart_protection_unmap_range((unsigned long)shmem_base,
-							trig_count * sizeof(*entry));
-			return SBI_ERR_FAILED;
-		}
-	}
+	if (trig_count > RV_MAX_TRIGGERS)
+		return SBI_ERR_INVALID_PARAM;
 
 	if (hs->available_trigs < trig_count) {
 		*out = hs->available_trigs;
-		sbi_hart_protection_unmap_range((unsigned long)shmem_base,
-					       trig_count * sizeof(*entry));
 		return SBI_ERR_FAILED;
 	}
 
-	/* Install triggers */
+	shmem_base = hart_shmem_base(hs);
+	sbi_hart_protection_map_range((unsigned long)shmem_base,
+				      trig_count * sizeof(*entry));
+
 	for_each_trig_entry(shmem_base, trig_count, typeof(*entry), entry) {
 		/*
-		 * Since we have already checked if enough triggers are
-		 * available, trigger allocation must succeed.
+		 * Snapshot one entry from shared memory so that S-mode
+		 * cannot modify it between validation and installation.
 		 */
-		trig = sbi_alloc_trigger();
+		local = entry->data;
+		ctrl = lle_to_cpu(local.tdata1);
 
-		recv = (struct sbi_dbtr_data_msg *)(&entry->data);
+		if (!dbtr_trigger_supported(TDATA1_GET_TYPE(ctrl)) ||
+		    !dbtr_trigger_valid(TDATA1_GET_TYPE(ctrl), ctrl)) {
+			*out = _idx;
+			goto rollback;
+		}
+
+		trig = sbi_alloc_trigger();
 		xmit = (struct sbi_dbtr_id_msg *)(&entry->id);
 
-		dbtr_trigger_setup(trig,  recv);
+		dbtr_trigger_setup(trig, &local);
 		dbtr_trigger_enable(trig);
 		xmit->idx = cpu_to_lle(trig->index);
-
+		installed[num_installed++] = trig;
 	}
 
 	sbi_hart_protection_unmap_range((unsigned long)shmem_base,
 					trig_count * sizeof(*entry));
 
 	return SBI_SUCCESS;
+
+rollback:
+	while (num_installed--) {
+		dbtr_trigger_clear(installed[num_installed]);
+		sbi_free_trigger(installed[num_installed]);
+	}
+	sbi_hart_protection_unmap_range((unsigned long)shmem_base,
+					trig_count * sizeof(*entry));
+	return SBI_ERR_FAILED;
 }
 
 int sbi_dbtr_uninstall_trig(unsigned long trig_idx_base,
-- 
2.34.1