linux-kernel - [PATCH v5 2/2] regmap: warn users about uninitialized flat cache

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20251023135032.229511-3-sander@svanheule.net>
Date: Thu, 23 Oct 2025 15:50:32 +0200
From: Sander Vanheule <sander@...nheule.net>
To: Mark Brown <broonie@...nel.org>,
	linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Danilo Krummrich <dakr@...nel.org>,
	Sander Vanheule <sander@...nheule.net>
Subject: [PATCH v5 2/2] regmap: warn users about uninitialized flat cache

The standard flat cache did not contain any validity info, so the cache
was always considered to be entirely valid. Multiple mechanisms exist to
initialize the cache on regmap init (defaults, raw defaults, HW init),
but not all drivers are using one of these. As a result, their
implementation might currently depend on the zero-initialized cache or
contain other workarounds.

When reading an uninitialized value from the flat cache, warn the user,
but maintain the current behavior. This will allow developers to switch
to a sparse (flat) cache independently.

Signed-off-by: Sander Vanheule <sander@...nheule.net>
---
Changes since v4:
- Use one line for the log message
- Use dev_warn_once() with test_bit() to avoid log flooding with offset
  register spaces

Changes since v3:
- New patch: emit a warning for the flat cache on suspicious registers
---
 drivers/base/regmap/regcache-flat.c | 18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

diff --git a/drivers/base/regmap/regcache-flat.c b/drivers/base/regmap/regcache-flat.c
index 1ca308916d5a..29934878ced6 100644
--- a/drivers/base/regmap/regcache-flat.c
+++ b/drivers/base/regmap/regcache-flat.c
@@ -91,6 +91,11 @@ static int regcache_flat_read(struct regmap *map,
 	struct regcache_flat_data *cache = map->cache;
 	unsigned int index = regcache_flat_get_index(map, reg);
 
+	/* legacy behavior: ignore validity, but warn the user */
+	if (unlikely(!test_bit(index, cache->valid)))
+		dev_warn_once(map->dev,
+			"using zero-initialized flat cache, this may cause unexpected behavior");
+
 	*value = cache->data[index];
 
 	return 0;
@@ -116,17 +121,6 @@ static int regcache_flat_write(struct regmap *map, unsigned int reg,
 	struct regcache_flat_data *cache = map->cache;
 	unsigned int index = regcache_flat_get_index(map, reg);
 
-	cache->data[index] = value;
-
-	return 0;
-}
-
-static int regcache_flat_sparse_write(struct regmap *map, unsigned int reg,
-				      unsigned int value)
-{
-	struct regcache_flat_data *cache = map->cache;
-	unsigned int index = regcache_flat_get_index(map, reg);
-
 	cache->data[index] = value;
 	__set_bit(index, cache->valid);
 
@@ -160,6 +154,6 @@ struct regcache_ops regcache_flat_sparse_ops = {
 	.init = regcache_flat_init,
 	.exit = regcache_flat_exit,
 	.read = regcache_flat_sparse_read,
-	.write = regcache_flat_sparse_write,
+	.write = regcache_flat_write,
 	.drop = regcache_flat_drop,
 };
-- 
2.51.0