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Date: Mon, 21 Mar 2016 12:09:24 -0400
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Subject: Re: [PATCH v2] drm/radeon: evergreen_hpd_init()/_fini(): fix HPD IRQ bitset
From: Alex Deucher <alexdeucher@gmail.com>
To: Nicolai Stange <nicstange@gmail.com>
Cc: David Airlie <airlied@linux.ie>, Alex Deucher <alexander.deucher@amd.com>,
        =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Maling list - DRI developers 
	<dri-devel@lists.freedesktop.org>
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On Mon, Mar 21, 2016 at 8:10 AM, Nicolai Stange <nicstange@gmail.com> wrote:
> The values of all but the RADEON_HPD_NONE members of the radeon_hpd_id
> enum transform 1:1 into bit positions within the 'enabled' bitset as
> assembled by evergreen_hpd_init():
>
>   enabled |= 1 << radeon_connector->hpd.hpd;
>
> However, if ->hpd.hpd happens to equal RADEON_HPD_NONE == 0xff, UBSAN
> reports
>
>   UBSAN: Undefined behaviour in drivers/gpu/drm/radeon/evergreen.c:1867:16
>   shift exponent 255 is too large for 32-bit type 'int'
>   [...]
>   Call Trace:
>    [<ffffffff818c4d35>] dump_stack+0xbc/0x117
>    [<ffffffff818c4c79>] ? _atomic_dec_and_lock+0x169/0x169
>    [<ffffffff819411bb>] ubsan_epilogue+0xd/0x4e
>    [<ffffffff81941cbc>] __ubsan_handle_shift_out_of_bounds+0x1fb/0x254
>    [<ffffffffa0ba7f2e>] ? atom_execute_table+0x3e/0x50 [radeon]
>    [<ffffffff81941ac1>] ? __ubsan_handle_load_invalid_value+0x158/0x158
>    [<ffffffffa0b87700>] ? radeon_get_pll_use_mask+0x130/0x130 [radeon]
>    [<ffffffff81219930>] ? wake_up_klogd_work_func+0x60/0x60
>    [<ffffffff8121a35e>] ? vprintk_default+0x3e/0x60
>    [<ffffffffa0c603c4>] evergreen_hpd_init+0x274/0x2d0 [radeon]
>    [<ffffffffa0c603c4>] ? evergreen_hpd_init+0x274/0x2d0 [radeon]
>    [<ffffffffa0bd196e>] radeon_modeset_init+0x8ce/0x18d0 [radeon]
>    [<ffffffffa0b71d86>] radeon_driver_load_kms+0x186/0x350 [radeon]
>    [<ffffffffa03b6b16>] drm_dev_register+0xc6/0x100 [drm]
>    [<ffffffffa03bc8c4>] drm_get_pci_dev+0xe4/0x490 [drm]
>    [<ffffffff814b83f0>] ? kfree+0x220/0x370
>    [<ffffffffa0b687c2>] radeon_pci_probe+0x112/0x140 [radeon]
>    [...]
>   =====================================================================
>   radeon 0000:01:00.0: No connectors reported connected with modes
>
> At least on x86, there should be no user-visible impact as there
>
>   1 << 0xff == 1 << (0xff & 31) == 1 << 31
>
> holds and 31 > RADEON_MAX_HPD_PINS. Thus, this patch is a cosmetic one.
>
> All of the above applies analogously to evergreen_hpd_fini().
>
> Silence UBSAN by checking ->hpd.hpd for RADEON_HPD_NONE before oring it
> into the 'enabled' bitset in evergreen_hpd_init() or the 'disabled' bitset
> in evergreen_hpd_fini() respectively.
>
> Signed-off-by: Nicolai Stange <nicstange@gmail.com>

Can you please fix all instances of this?  This same pattern is
repeated in various asic families.

Alex


> ---
>  Applicable to linux-next-20160321.
>
>  Changes to v1:
>  - Turn commit message's impact part into a non-impact part.
>
>  drivers/gpu/drm/radeon/evergreen.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/radeon/evergreen.c b/drivers/gpu/drm/radeon/evergreen.c
> index 76c4bdf..6360717 100644
> --- a/drivers/gpu/drm/radeon/evergreen.c
> +++ b/drivers/gpu/drm/radeon/evergreen.c
> @@ -1864,7 +1864,8 @@ void evergreen_hpd_init(struct radeon_device *rdev)
>                         break;
>                 }
>                 radeon_hpd_set_polarity(rdev, radeon_connector->hpd.hpd);
> -               enabled |= 1 << radeon_connector->hpd.hpd;
> +               if (radeon_connector->hpd.hpd != RADEON_HPD_NONE)
> +                       enabled |= 1 << radeon_connector->hpd.hpd;
>         }
>         radeon_irq_kms_enable_hpd(rdev, enabled);
>  }
> @@ -1907,7 +1908,8 @@ void evergreen_hpd_fini(struct radeon_device *rdev)
>                 default:
>                         break;
>                 }
> -               disabled |= 1 << radeon_connector->hpd.hpd;
> +               if (radeon_connector->hpd.hpd != RADEON_HPD_NONE)
> +                       disabled |= 1 << radeon_connector->hpd.hpd;
>         }
>         radeon_irq_kms_disable_hpd(rdev, disabled);
>  }
> --
> 2.7.3
>
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