kasan: remove atomic accesses to stack ring entries

Remove the atomic accesses to entry fields in save_stack_info and
kasan_complete_mode_report_info for tag-based KASAN modes.

These atomics are not required, as the read/write lock prevents the
entries from being read (in kasan_complete_mode_report_info) while being
written (in save_stack_info) and the try_cmpxchg prevents the same entry
from being rewritten (in save_stack_info) in the unlikely case of wrapping
during writing.

Link: https://lkml.kernel.org/r/29f59126d9845c5257b6c29cd7ad113b16f19f47.1700502145.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Marco Elver <elver@google.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/kasan/report_tags.c b/mm/kasan/report_tags.c
index 8b8bfdb..78abdcd 100644 (file)
--- a/mm/kasan/report_tags.c
+++ b/mm/kasan/report_tags.c
@@ -31,10 +31,6 @@ void kasan_complete_mode_report_info(struct kasan_report_info *info)
        unsigned long flags;
        u64 pos;
        struct kasan_stack_ring_entry *entry;
-       void *ptr;
-       u32 pid;
-       depot_stack_handle_t stack;
-       bool is_free;
        bool alloc_found = false, free_found = false;
 
        if ((!info->cache || !info->object) && !info->bug_type) {
@@ -61,18 +57,11 @@ void kasan_complete_mode_report_info(struct kasan_report_info *info)
 
                entry = &stack_ring.entries[i % stack_ring.size];
 
-               /* Paired with smp_store_release() in save_stack_info(). */
-               ptr = (void *)smp_load_acquire(&entry->ptr);
-
-               if (kasan_reset_tag(ptr) != info->object ||
-                   get_tag(ptr) != get_tag(info->access_addr))
+               if (kasan_reset_tag(entry->ptr) != info->object ||
+                   get_tag(entry->ptr) != get_tag(info->access_addr))
                        continue;
 
-               pid = READ_ONCE(entry->pid);
-               stack = READ_ONCE(entry->stack);
-               is_free = READ_ONCE(entry->is_free);
-
-               if (is_free) {
+               if (entry->is_free) {
                        /*
                         * Second free of the same object.
                         * Give up on trying to find the alloc entry.
@@ -80,8 +69,8 @@ void kasan_complete_mode_report_info(struct kasan_report_info *info)
                        if (free_found)
                                break;
 
-                       info->free_track.pid = pid;
-                       info->free_track.stack = stack;
+                       info->free_track.pid = entry->pid;
+                       info->free_track.stack = entry->stack;
                        free_found = true;
 
                        /*
@@ -95,8 +84,8 @@ void kasan_complete_mode_report_info(struct kasan_report_info *info)
                        if (alloc_found)
                                break;
 
-                       info->alloc_track.pid = pid;
-                       info->alloc_track.stack = stack;
+                       info->alloc_track.pid = entry->pid;
+                       info->alloc_track.stack = entry->stack;
                        alloc_found = true;
 
                        /*

diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c
index 4fd3212..b6c017e 100644 (file)
--- a/mm/kasan/tags.c
+++ b/mm/kasan/tags.c
@@ -121,15 +121,12 @@ next:
        if (!try_cmpxchg(&entry->ptr, &old_ptr, STACK_RING_BUSY_PTR))
                goto next; /* Busy slot. */
 
-       WRITE_ONCE(entry->size, cache->object_size);
-       WRITE_ONCE(entry->pid, current->pid);
-       WRITE_ONCE(entry->stack, stack);
-       WRITE_ONCE(entry->is_free, is_free);
+       entry->size = cache->object_size;
+       entry->pid = current->pid;
+       entry->stack = stack;
+       entry->is_free = is_free;
 
-       /*
-        * Paired with smp_load_acquire() in kasan_complete_mode_report_info().
-        */
-       smp_store_release(&entry->ptr, (s64)object);
+       entry->ptr = object;
 
        read_unlock_irqrestore(&stack_ring.lock, flags);
 }