[PATCH v2] riscv: Safely remove entries from relocation list

[Charlie Jenkins <charlie@rivosinc.com>]

Use the safe versions of list and hlist iteration to safely remove
entries from the module relocation lists. To allow mutliple threads to
load modules concurrently, move relocation list pointers onto the stack
rather than using global variables.

Fixes: 8fd6c5142395 ("riscv: Add remaining module relocations")
Reported-by: Ron Economos <re@w6rz.net>
Closes: https://lore.kernel.org/linux-riscv/444de86a-7e7c-4de7-5d1d-c1c40eefa4ba@w6rz.net
Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
---
Changes in v2:
- Support linking modules concurrently across threads.
- Link to v1: https://lore.kernel.org/r/20231120-module_linking_freeing-v1-1-fff81d7289fc@rivosinc.com
---
 arch/riscv/kernel/module.c | 76 +++++++++++++++++++++++++++++++---------------
 1 file changed, 51 insertions(+), 25 deletions(-)

diff --git a/arch/riscv/kernel/module.c b/arch/riscv/kernel/module.c
index 56a8c78e9e21..f53e82b70dff 100644
--- a/arch/riscv/kernel/module.c
+++ b/arch/riscv/kernel/module.c
@@ -40,14 +40,17 @@ struct relocation_handlers {
 				  long buffer);
 };
 
-unsigned int initialize_relocation_hashtable(unsigned int num_relocations);
-void process_accumulated_relocations(struct module *me);
+unsigned int
+initialize_relocation_hashtable(unsigned int num_relocations,
+				struct hlist_head **relocation_hashtable,
+				struct list_head *used_buckets_list);
+void process_accumulated_relocations(struct module *me,
+				     struct hlist_head **relocation_hashtable,
+				     struct list_head *used_buckets_list);
 int add_relocation_to_accumulate(struct module *me, int type, void *location,
-				 unsigned int hashtable_bits, Elf_Addr v);
-
-struct hlist_head *relocation_hashtable;
-
-struct list_head used_buckets_list;
+				 unsigned int hashtable_bits, Elf_Addr v,
+				struct hlist_head **relocation_hashtable,
+				struct list_head *used_buckets_list);
 
 /*
  * The auipc+jalr instruction pair can reach any PC-relative offset
@@ -604,7 +607,9 @@ static const struct relocation_handlers reloc_handlers[] = {
 	/* 192-255 nonstandard ABI extensions  */
 };
 
-void process_accumulated_relocations(struct module *me)
+void process_accumulated_relocations(struct module *me,
+				     struct hlist_head **relocation_hashtable,
+				     struct list_head *used_buckets_list)
 {
 	/*
 	 * Only ADD/SUB/SET/ULEB128 should end up here.
@@ -624,18 +629,25 @@ void process_accumulated_relocations(struct module *me)
 	 *	- Each relocation entry for a location address
 	 */
 	struct used_bucket *bucket_iter;
+	struct used_bucket *bucket_iter_tmp;
 	struct relocation_head *rel_head_iter;
+	struct hlist_node *rel_head_iter_tmp;
 	struct relocation_entry *rel_entry_iter;
+	struct relocation_entry *rel_entry_iter_tmp;
 	int curr_type;
 	void *location;
 	long buffer;
 
-	list_for_each_entry(bucket_iter, &used_buckets_list, head) {
-		hlist_for_each_entry(rel_head_iter, bucket_iter->bucket, node) {
+	list_for_each_entry_safe(bucket_iter, bucket_iter_tmp,
+				 used_buckets_list, head) {
+		hlist_for_each_entry_safe(rel_head_iter, rel_head_iter_tmp,
+					  bucket_iter->bucket, node) {
 			buffer = 0;
 			location = rel_head_iter->location;
-			list_for_each_entry(rel_entry_iter,
-					    rel_head_iter->rel_entry, head) {
+			list_for_each_entry_safe(rel_entry_iter,
+						 rel_entry_iter_tmp,
+						 rel_head_iter->rel_entry,
+						 head) {
 				curr_type = rel_entry_iter->type;
 				reloc_handlers[curr_type].reloc_handler(
 					me, &buffer, rel_entry_iter->value);
@@ -648,11 +660,13 @@ void process_accumulated_relocations(struct module *me)
 		kfree(bucket_iter);
 	}
 
-	kfree(relocation_hashtable);
+	kfree(*relocation_hashtable);
 }
 
 int add_relocation_to_accumulate(struct module *me, int type, void *location,
-				 unsigned int hashtable_bits, Elf_Addr v)
+				 unsigned int hashtable_bits, Elf_Addr v,
+				struct hlist_head **relocation_hashtable,
+				struct list_head *used_buckets_list)
 {
 	struct relocation_entry *entry;
 	struct relocation_head *rel_head;
@@ -667,7 +681,7 @@ int add_relocation_to_accumulate(struct module *me, int type, void *location,
 
 	hash = hash_min((uintptr_t)location, hashtable_bits);
 
-	current_head = &relocation_hashtable[hash];
+	current_head = &((*relocation_hashtable)[hash]);
 
 	/* Find matching location (if any) */
 	bool found = false;
@@ -693,7 +707,7 @@ int add_relocation_to_accumulate(struct module *me, int type, void *location,
 				kmalloc(sizeof(struct used_bucket), GFP_KERNEL);
 			INIT_LIST_HEAD(&bucket->head);
 			bucket->bucket = current_head;
-			list_add(&bucket->head, &used_buckets_list);
+			list_add(&bucket->head, used_buckets_list);
 		}
 		hlist_add_head(&rel_head->node, current_head);
 	}
@@ -704,7 +718,10 @@ int add_relocation_to_accumulate(struct module *me, int type, void *location,
 	return 0;
 }
 
-unsigned int initialize_relocation_hashtable(unsigned int num_relocations)
+unsigned int
+initialize_relocation_hashtable(unsigned int num_relocations,
+				struct hlist_head **relocation_hashtable,
+				struct list_head *used_buckets_list)
 {
 	/* Can safely assume that bits is not greater than sizeof(long) */
 	unsigned long hashtable_size = roundup_pow_of_two(num_relocations);
@@ -720,12 +737,12 @@ unsigned int initialize_relocation_hashtable(unsigned int num_relocations)
 
 	hashtable_size <<= should_double_size;
 
-	relocation_hashtable = kmalloc_array(hashtable_size,
-					     sizeof(*relocation_hashtable),
-					     GFP_KERNEL);
-	__hash_init(relocation_hashtable, hashtable_size);
+	*relocation_hashtable = kmalloc_array(hashtable_size,
+					      sizeof(*relocation_hashtable),
+					      GFP_KERNEL);
+	__hash_init(*relocation_hashtable, hashtable_size);
 
-	INIT_LIST_HEAD(&used_buckets_list);
+	INIT_LIST_HEAD(used_buckets_list);
 
 	return hashtable_bits;
 }
@@ -742,7 +759,13 @@ int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
 	Elf_Addr v;
 	int res;
 	unsigned int num_relocations = sechdrs[relsec].sh_size / sizeof(*rel);
-	unsigned int hashtable_bits = initialize_relocation_hashtable(num_relocations);
+	struct hlist_head *relocation_hashtable;
+	struct list_head used_buckets_list;
+	unsigned int hashtable_bits;
+
+	hashtable_bits = initialize_relocation_hashtable(num_relocations,
+							 &relocation_hashtable,
+							 &used_buckets_list);
 
 	pr_debug("Applying relocate section %u to %u\n", relsec,
 	       sechdrs[relsec].sh_info);
@@ -823,14 +846,17 @@ int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
 		}
 
 		if (reloc_handlers[type].accumulate_handler)
-			res = add_relocation_to_accumulate(me, type, location, hashtable_bits, v);
+			res = add_relocation_to_accumulate(
+				me, type, location, hashtable_bits, v,
+				&relocation_hashtable, &used_buckets_list);
 		else
 			res = handler(me, location, v);
 		if (res)
 			return res;
 	}
 
-	process_accumulated_relocations(me);
+	process_accumulated_relocations(me, &relocation_hashtable,
+					&used_buckets_list);
 
 	return 0;
 }

---
base-commit: 98b1cc82c4affc16f5598d4fa14b1858671b2263
change-id: 20231120-module_linking_freeing-2b5a3b255b5e
-- 
- Charlie