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riscv: Safely remove entries from relocation list
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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: 8fd6c51 ("riscv: Add remaining module relocations")
Reported-by: Ron Economos <[email protected]>
Closes: https://lore.kernel.org/linux-riscv/[email protected]
Signed-off-by: Charlie Jenkins <[email protected]>
Tested-by: Björn Töpel <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Palmer Dabbelt <[email protected]>
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@charlie-rivos @palmer-dabbelt
charlie-rivos authored and palmer-dabbelt committed Dec 4, 2023
1 parent b85ea95 commit d8792a5
Showing 1 changed file with 82 additions and 28 deletions.
110 changes: 82 additions & 28 deletions arch/riscv/kernel/module.c
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Original file line number Diff line number Diff line change
Expand Up @@ -40,15 +40,6 @@ struct relocation_handlers {
long buffer);
};

unsigned int initialize_relocation_hashtable(unsigned int num_relocations);
void process_accumulated_relocations(struct module *me);
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;

/*
* The auipc+jalr instruction pair can reach any PC-relative offset
* in the range [-2^31 - 2^11, 2^31 - 2^11)
Expand Down Expand Up @@ -604,7 +595,10 @@ static const struct relocation_handlers reloc_handlers[] = {
/* 192-255 nonstandard ABI extensions */
};

void process_accumulated_relocations(struct module *me)
static 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.
Expand All @@ -624,18 +618,25 @@ 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);
Expand All @@ -648,11 +649,14 @@ 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)
static 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)
{
struct relocation_entry *entry;
struct relocation_head *rel_head;
Expand All @@ -661,6 +665,10 @@ int add_relocation_to_accumulate(struct module *me, int type, void *location,
unsigned long hash;

entry = kmalloc(sizeof(*entry), GFP_KERNEL);

if (!entry)
return -ENOMEM;

INIT_LIST_HEAD(&entry->head);
entry->type = type;
entry->value = v;
Expand All @@ -669,7 +677,10 @@ int add_relocation_to_accumulate(struct module *me, int type, void *location,

current_head = &relocation_hashtable[hash];

/* Find matching location (if any) */
/*
* Search for the relocation_head for the relocations that happen at the
* provided location
*/
bool found = false;
struct relocation_head *rel_head_iter;

Expand All @@ -681,19 +692,45 @@ int add_relocation_to_accumulate(struct module *me, int type, void *location,
}
}

/*
* If there has not yet been any relocations at the provided location,
* create a relocation_head for that location and populate it with this
* relocation_entry.
*/
if (!found) {
rel_head = kmalloc(sizeof(*rel_head), GFP_KERNEL);

if (!rel_head) {
kfree(entry);
return -ENOMEM;
}

rel_head->rel_entry =
kmalloc(sizeof(struct list_head), GFP_KERNEL);

if (!rel_head->rel_entry) {
kfree(entry);
kfree(rel_head);
return -ENOMEM;
}

INIT_LIST_HEAD(rel_head->rel_entry);
rel_head->location = location;
INIT_HLIST_NODE(&rel_head->node);
if (!current_head->first) {
bucket =
kmalloc(sizeof(struct used_bucket), GFP_KERNEL);

if (!bucket) {
kfree(entry);
kfree(rel_head);
kfree(rel_head->rel_entry);
return -ENOMEM;
}

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);
}
Expand All @@ -704,7 +741,9 @@ int add_relocation_to_accumulate(struct module *me, int type, void *location,
return 0;
}

unsigned int initialize_relocation_hashtable(unsigned int num_relocations)
static unsigned int
initialize_relocation_hashtable(unsigned int num_relocations,
struct hlist_head **relocation_hashtable)
{
/* Can safely assume that bits is not greater than sizeof(long) */
unsigned long hashtable_size = roundup_pow_of_two(num_relocations);
Expand All @@ -720,12 +759,13 @@ 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);
if (!*relocation_hashtable)
return -ENOMEM;

INIT_LIST_HEAD(&used_buckets_list);
__hash_init(*relocation_hashtable, hashtable_size);

return hashtable_bits;
}
Expand All @@ -742,7 +782,17 @@ 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);

if (hashtable_bits < 0)
return hashtable_bits;

INIT_LIST_HEAD(&used_buckets_list);

pr_debug("Applying relocate section %u to %u\n", relsec,
sechdrs[relsec].sh_info);
Expand Down Expand Up @@ -823,14 +873,18 @@ 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;
}
Expand Down

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