Re: [PATCH net] net: ena: fix shift-out-of-bounds in exponential backoff

[Leon Romanovsky <leon@kernel.org>]

On Mon, Jul 10, 2023 at 06:36:21PM -0700, Krister Johansen wrote:
> The ENA adapters on our instances occasionally reset.  Once recently
> logged a UBSAN failure to console in the process:
> 
>   UBSAN: shift-out-of-bounds in build/linux/drivers/net/ethernet/amazon/ena/ena_com.c:540:13
>   shift exponent 32 is too large for 32-bit type 'unsigned int'
>   CPU: 28 PID: 70012 Comm: kworker/u72:2 Kdump: loaded not tainted 5.15.117
>   Hardware name: Amazon EC2 c5d.9xlarge/, BIOS 1.0 10/16/2017
>   Workqueue: ena ena_fw_reset_device [ena]
>   Call Trace:
>   <TASK>
>   dump_stack_lvl+0x4a/0x63
>   dump_stack+0x10/0x16
>   ubsan_epilogue+0x9/0x36
>   __ubsan_handle_shift_out_of_bounds.cold+0x61/0x10e
>   ? __const_udelay+0x43/0x50
>   ena_delay_exponential_backoff_us.cold+0x16/0x1e [ena]
>   wait_for_reset_state+0x54/0xa0 [ena]
>   ena_com_dev_reset+0xc8/0x110 [ena]
>   ena_down+0x3fe/0x480 [ena]
>   ena_destroy_device+0xeb/0xf0 [ena]
>   ena_fw_reset_device+0x30/0x50 [ena]
>   process_one_work+0x22b/0x3d0
>   worker_thread+0x4d/0x3f0
>   ? process_one_work+0x3d0/0x3d0
>   kthread+0x12a/0x150
>   ? set_kthread_struct+0x50/0x50
>   ret_from_fork+0x22/0x30
>   </TASK>
> 
> Apparently, the reset delays are getting so large they can trigger a
> UBSAN panic.
> 
> Looking at the code, the current timeout is capped at 5000us.  Using a
> base value of 100us, the current code will overflow after (1<<29).  Even
> at values before 32, this function wraps around, perhaps
> unintentionally.
> 
> Cap the value of the exponent used for this backoff at (1<<16) which is
> larger than currently necessary, but large enough to support bigger
> values in the future.
> 
> Cc: stable@vger.kernel.org
> Fixes: 4bb7f4cf60e3 ("net: ena: reduce driver load time")
> Signed-off-by: Krister Johansen <kjlx@templeofstupid.com>
> ---
>  drivers/net/ethernet/amazon/ena/ena_com.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/net/ethernet/amazon/ena/ena_com.c b/drivers/net/ethernet/amazon/ena/ena_com.c
> index 451c3a1b6255..633b321d7fdd 100644
> --- a/drivers/net/ethernet/amazon/ena/ena_com.c
> +++ b/drivers/net/ethernet/amazon/ena/ena_com.c
> @@ -35,6 +35,8 @@
>  
>  #define ENA_REGS_ADMIN_INTR_MASK 1
>  
> +#define ENA_MAX_BACKOFF_DELAY_EXP 16U
> +
>  #define ENA_MIN_ADMIN_POLL_US 100
>  
>  #define ENA_MAX_ADMIN_POLL_US 5000
> @@ -536,6 +538,7 @@ static int ena_com_comp_status_to_errno(struct ena_com_admin_queue *admin_queue,
>  
>  static void ena_delay_exponential_backoff_us(u32 exp, u32 delay_us)
>  {
> +	exp = min_t(u32, exp, ENA_MAX_BACKOFF_DELAY_EXP);

Thanks,
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>