[SeaBIOS] [SEABIOS] [PATCH 1/1] nvme: fix I/O queue length calculation overflow

[Kevin O'Connor]

On Sun, Aug 12, 2018 at 03:42:40PM -0500, Matt DeVillier wrote:
> Commit cd47172 changed the I/O queue length calculation to use the
> Maximum Queue Entries Supported (MQES) value from the capabilities
> register, plus one, with a maximum value of NVME_PAGE_SIZE.
> 
> An unintended effect from this is that a MQES value of 0xFFFF yields
> a length of zero, resulting in the queue allocation failing. Fix this
> by checking for a zero length when checking that the length exceeds
> NVME_PAGE_SIZE, and setting to NVME_PAGE_SIZE.
> 
> TEST: build/boot on a Purism Librem13v2 with a MyDigitalSSD BPX NVMe
> drive, which reports a MQES of 0xFFFF. Verify NVMe drive present in
> boot menu and OS boots successfully.
> 
> Signed-off-by: Matt DeVillier <matt.devillier at gmail.com>
> ---
>  src/hw/nvme.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/src/hw/nvme.c b/src/hw/nvme.c
> index e6d739d..c2d6863 100644
> --- a/src/hw/nvme.c
> +++ b/src/hw/nvme.c
> @@ -319,7 +319,7 @@ nvme_create_io_cq(struct nvme_ctrl *ctrl, struct
> nvme_cq *cq, u16 q_idx)
>      int rc;
>      struct nvme_sqe *cmd_create_cq;
>      u16 length = 1 + (ctrl->reg->cap & 0xffff);
> -    if (length > NVME_PAGE_SIZE / sizeof(struct nvme_cqe))
> +    if (length == 0 || length > NVME_PAGE_SIZE / sizeof(struct nvme_cqe))
>          length = NVME_PAGE_SIZE / sizeof(struct nvme_cqe);

Thanks.  Instead of changing the if statement, could we just change
length here to a u32 to avoid this issue?

> 
>      rc = nvme_init_cq(ctrl, cq, q_idx, length);
> @@ -363,7 +363,7 @@ nvme_create_io_sq(struct nvme_ctrl *ctrl, struct
> nvme_sq *sq, u16 q_idx, struct
>      int rc;
>      struct nvme_sqe *cmd_create_sq;
>      u16 length = 1 + (ctrl->reg->cap & 0xffff);
> -    if (length > NVME_PAGE_SIZE / sizeof(struct nvme_cqe))
> +    if (length == 0 || length > NVME_PAGE_SIZE / sizeof(struct nvme_cqe))
>          length = NVME_PAGE_SIZE / sizeof(struct nvme_cqe);
> 
>      rc = nvme_init_sq(ctrl, sq, q_idx, length, cq);
> -- 
> 2.17.1

-Kevin