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Date:   Mon, 24 Sep 2018 20:19:24 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     linux-block <linux-block@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sunvdc: Remove VLA usage

On Wed, Sep 5, 2018 at 5:09 PM, Kees Cook <keescook@...omium.org> wrote:
> In the quest to remove all stack VLA usage from the kernel[1], this
> moves the math for cookie calculation into macros and allocates a fixed
> size array for the maximum number of cookies and adds a runtime sanity check.
> (Note that the size was always fixed, but just hidden from the compiler.)
>
> [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
>
> Signed-off-by: Kees Cook <keescook@...omium.org>

Friendly ping. Jens, can you take this?

Thanks!

-Kees

> ---
>  drivers/block/sunvdc.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/block/sunvdc.c b/drivers/block/sunvdc.c
> index 5ca56bfae63c..f68e9baffad7 100644
> --- a/drivers/block/sunvdc.c
> +++ b/drivers/block/sunvdc.c
> @@ -36,6 +36,10 @@ MODULE_VERSION(DRV_MODULE_VERSION);
>  #define VDC_TX_RING_SIZE       512
>  #define VDC_DEFAULT_BLK_SIZE   512
>
> +#define MAX_XFER_BLKS          (128 * 1024)
> +#define MAX_XFER_SIZE          (MAX_XFER_BLKS / VDC_DEFAULT_BLK_SIZE)
> +#define MAX_RING_COOKIES       ((MAX_XFER_BLKS / PAGE_SIZE) + 2)
> +
>  #define WAITING_FOR_LINK_UP    0x01
>  #define WAITING_FOR_TX_SPACE   0x02
>  #define WAITING_FOR_GEN_CMD    0x04
> @@ -450,7 +454,7 @@ static int __send_request(struct request *req)
>  {
>         struct vdc_port *port = req->rq_disk->private_data;
>         struct vio_dring_state *dr = &port->vio.drings[VIO_DRIVER_TX_RING];
> -       struct scatterlist sg[port->ring_cookies];
> +       struct scatterlist sg[MAX_RING_COOKIES];
>         struct vdc_req_entry *rqe;
>         struct vio_disk_desc *desc;
>         unsigned int map_perm;
> @@ -458,6 +462,9 @@ static int __send_request(struct request *req)
>         u64 len;
>         u8 op;
>
> +       if (WARN_ON(port->ring_cookies > MAX_RING_COOKIES))
> +               return -EINVAL;
> +
>         map_perm = LDC_MAP_SHADOW | LDC_MAP_DIRECT | LDC_MAP_IO;
>
>         if (rq_data_dir(req) == READ) {
> @@ -984,9 +991,8 @@ static int vdc_port_probe(struct vio_dev *vdev, const struct vio_device_id *id)
>                 goto err_out_free_port;
>
>         port->vdisk_block_size = VDC_DEFAULT_BLK_SIZE;
> -       port->max_xfer_size = ((128 * 1024) / port->vdisk_block_size);
> -       port->ring_cookies = ((port->max_xfer_size *
> -                              port->vdisk_block_size) / PAGE_SIZE) + 2;
> +       port->max_xfer_size = MAX_XFER_SIZE;
> +       port->ring_cookies = MAX_RING_COOKIES;
>
>         err = vio_ldc_alloc(&port->vio, &vdc_ldc_cfg, port);
>         if (err)
> --
> 2.17.1
>
>
> --
> Kees Cook
> Pixel Security



-- 
Kees Cook
Pixel Security

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