Re: [PATCH] net/mlx4_core: Avoid impossible mlx4_db_alloc() order value

On Tue, Feb 11, 2025 at 6:22 AM Tariq Toukan [off-list ref] wrote:

On 11/02/2025 2:01, Justin Stitt wrote:

quoted

On Mon, Feb 10, 2025 at 09:45:05AM -0800, Kees Cook wrote:

quoted

GCC can see that the value range for "order" is capped, but this leads
it to consider that it might be negative, leading to a false positive
warning (with GCC 15 with -Warray-bounds -fdiagnostics-details):

../drivers/net/ethernet/mellanox/mlx4/alloc.c:691:47: error: array subscript -1 is below array bounds of 'long unsigned int *[2]' [-Werror=array-bounds=]
   691 |                 i = find_first_bit(pgdir->bits[o], MLX4_DB_PER_PAGE >> o);
       |                                    ~~~~~~~~~~~^~~
   'mlx4_alloc_db_from_pgdir': events 1-2
   691 |                 i = find_first_bit(pgdir->bits[o], MLX4_DB_PER_PAGE >> o);                        |                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
       |                     |                         |                                                   |                     |                         (2) out of array bounds here
       |                     (1) when the condition is evaluated to true                             In file included from ../drivers/net/ethernet/mellanox/mlx4/mlx4.h:53,
                  from ../drivers/net/ethernet/mellanox/mlx4/alloc.c:42:
../include/linux/mlx4/device.h:664:33: note: while referencing 'bits'
   664 |         unsigned long          *bits[2];
       |                                 ^~~~

Switch the argument to unsigned int, which removes the compiler needing
to consider negative values.

Signed-off-by: Kees Cook <kees@kernel.org>
---
Cc: Tariq Toukan <tariqt@nvidia.com>
Cc: Andrew Lunn <andrew+netdev@lunn.ch>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <redacted>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Yishai Hadas <yishaih@nvidia.com>
Cc: netdev@vger.kernel.org
Cc: linux-rdma@vger.kernel.org
---
  drivers/net/ethernet/mellanox/mlx4/alloc.c | 6 +++---
  include/linux/mlx4/device.h                | 2 +-
  2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx4/alloc.c b/drivers/net/ethernet/mellanox/mlx4/alloc.c
index b330020dc0d6..f2bded847e61 100644
--- a/drivers/net/ethernet/mellanox/mlx4/alloc.c
+++ b/drivers/net/ethernet/mellanox/mlx4/alloc.c

@@ -682,9 +682,9 @@ static struct mlx4_db_pgdir *mlx4_alloc_db_pgdir(struct device *dma_device)
  }

  static int mlx4_alloc_db_from_pgdir(struct mlx4_db_pgdir *pgdir,
-                                struct mlx4_db *db, int order)
+                                struct mlx4_db *db, unsigned int order)
  {
-    int o;
+    unsigned int o;
     int i;

     for (o = order; o <= 1; ++o) {

   ^ Knowing now that @order can only be 0 or 1 can this for loop (and
   goto) be dropped entirely?

Maybe I'm missing something...
Can you please explain why you think this can be dropped?

I meant "rewritten to use two if statements" instead of "dropped". I
think "replaced" or "refactored" was the word I wanted.

quoted

   The code is already short and sweet so I don't feel strongly either
   way.

quoted

@@ -712,7 +712,7 @@ static int mlx4_alloc_db_from_pgdir(struct mlx4_db_pgdir *pgdir,
     return 0;
  }

-int mlx4_db_alloc(struct mlx4_dev *dev, struct mlx4_db *db, int order)
+int mlx4_db_alloc(struct mlx4_dev *dev, struct mlx4_db *db, unsigned int order)
  {
     struct mlx4_priv *priv = mlx4_priv(dev);
     struct mlx4_db_pgdir *pgdir;

diff --git a/include/linux/mlx4/device.h b/include/linux/mlx4/device.h
index 27f42f713c89..86f0f2a25a3d 100644
--- a/include/linux/mlx4/device.h
+++ b/include/linux/mlx4/device.h

@@ -1135,7 +1135,7 @@ int mlx4_write_mtt(struct mlx4_dev *dev, struct mlx4_mtt *mtt,
  int mlx4_buf_write_mtt(struct mlx4_dev *dev, struct mlx4_mtt *mtt,
                    struct mlx4_buf *buf);

-int mlx4_db_alloc(struct mlx4_dev *dev, struct mlx4_db *db, int order);
+int mlx4_db_alloc(struct mlx4_dev *dev, struct mlx4_db *db, unsigned int order);
  void mlx4_db_free(struct mlx4_dev *dev, struct mlx4_db *db);

  int mlx4_alloc_hwq_res(struct mlx4_dev *dev, struct mlx4_hwq_resources *wqres,
--

2.34.1

Justin