linux-kernel - Re: [PATCH] media: chips-media: wave5: fix panic on decoding DECODED_IDX_FLAG

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Message-ID: <42c1c5e14a30730bc140b6791f25e55d434aa4e3.camel@ndufresne.ca>
Date:   Fri, 01 Dec 2023 15:18:42 -0500
From:   Nicolas Dufresne <nicolas@...fresne.ca>
To:     Mattijs Korpershoek <mkorpershoek@...libre.com>,
        Nas Chung <nas.chung@...psnmedia.com>,
        Jackson Lee <jackson.lee@...psnmedia.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>
Cc:     Guillaume La Roque <glaroque@...libre.com>,
        Brandon Brnich <b-brnich@...com>,
        Sebastian Fricke <sebastian.fricke@...labora.com>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: chips-media: wave5: fix panic on decoding
 DECODED_IDX_FLAG_SKIP

Hi Mattijs,

Le mercredi 29 novembre 2023 à 11:37 +0100, Mattijs Korpershoek a écrit :
> The display frame region information received from the vpu also
> contains the frame display index: info->index_frame_display.
> 
> This index, being a s32, can be negative when a skip option is passed.
> In that case, its value is DECODED_IDX_FLAG_SKIP (-2).
> 
> When disp_idx == -2, the following exception occurs:
> 
> [ 1530.782246][ T1900] Hardware name: Texas Instruments AM62P5 SK (DT)
> [ 1530.788501][ T1900] pstate: a0400005 (NzCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> [ 1530.796144][ T1900] pc : wave5_vpu_dec_get_output_info+0x300/0x308 [wave5]
> [ 1530.803060][ T1900] lr : wave5_vpu_dec_get_output_info+0x80/0x308 [wave5]
> [ 1530.809873][ T1900] sp : ffffffc00b85bc00
> [ 1530.813872][ T1900] x29: ffffffc00b85bc00 x28: 0000000000000000 x27: 0000000000000001
> [ 1530.821695][ T1900] x26: 00000000fffffffd x25: 00000000ffffffff x24: ffffff8812820000
> [ 1530.829516][ T1900] x23: ffffff88199f7840 x22: ffffff8873f5e000 x21: ffffffc00b85bc58
> [ 1530.837336][ T1900] x20: 0000000000000000 x19: ffffff88199f7920 x18: ffffffc00a899030
> [ 1530.845156][ T1900] x17: 00000000529c6ef0 x16: 00000000529c6ef0 x15: 0000000000198487
> [ 1530.852975][ T1900] x14: ffffffc009f2b650 x13: 0000000000058016 x12: 0000000005000000
> [ 1530.860795][ T1900] x11: 0000000000000000 x10: 0000000000000000 x9 : 0000000000000000
> [ 1530.868615][ T1900] x8 : 0000000000000000 x7 : 0000000000000000 x6 : 0000000000004086
> [ 1530.876434][ T1900] x5 : 0000000000000001 x4 : ffffffc001454b94 x3 : ffffffc001454d94
> [ 1530.884256][ T1900] x2 : ffffffc00b8201d0 x1 : 0000000000000020 x0 : 0000000000000000
> [ 1530.892087][ T1900] Call trace:
> [ 1530.895225][ T1900]  wave5_vpu_dec_get_output_info+0x300/0x308 [wave5]
> [ 1530.901788][ T1900]  wave5_vpu_dec_finish_decode+0x6c/0x3dc [wave5]
> [ 1530.908081][ T1900]  wave5_vpu_irq_thread+0x140/0x168 [wave5]
> [ 1530.913856][ T1900]  irq_thread_fn+0x44/0xa4
> [ 1530.918154][ T1900]  irq_thread+0x15c/0x288
> [ 1530.922330][ T1900]  kthread+0x104/0x1d4
> [ 1530.926247][ T1900]  ret_from_fork+0x10/0x20
> [ 1530.930520][ T1900] Code: 2a1f03ea 2a1f03eb 35ffef2c 17ffff74 (d42aa240)
> [ 1530.937296][ T1900] ---[ end trace 0000000000000000 ]---
> [ 1530.942596][ T1900] Kernel panic - not syncing: BRK handler: Fatal exception
> [ 1530.949629][ T1900] SMP: stopping secondary CPUs
> [ 1530.954244][ T1900] Kernel Offset: disabled
> [ 1530.958415][ T1900] CPU features: 0x00,00000000,00800184,0000421b
> [ 1530.964496][ T1900] Memory Limit: none
> 
> Move the disp_info assignment after testing that the index is positive
> to avoid the exception.
> 
> Fixes: 45d1a2b93277 ("media: chips-media: wave5: Add vpuapi layer")
> Signed-off-by: Mattijs Korpershoek <mkorpershoek@...libre.com>
> ---
>  drivers/media/platform/chips-media/wave5/wave5-vpuapi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/media/platform/chips-media/wave5/wave5-vpuapi.c b/drivers/media/platform/chips-media/wave5/wave5-vpuapi.c
> index 86b3993722db..1a3efb638dde 100644
> --- a/drivers/media/platform/chips-media/wave5/wave5-vpuapi.c
> +++ b/drivers/media/platform/chips-media/wave5/wave5-vpuapi.c
> @@ -508,8 +508,8 @@ int wave5_vpu_dec_get_output_info(struct vpu_instance *inst, struct dec_output_i
>  	info->rc_decoded = rect_info;
>  
>  	disp_idx = info->index_frame_display;
> -	disp_info = &p_dec_info->dec_out_info[disp_idx];
>  	if (info->index_frame_display >= 0 && info->index_frame_display < WAVE5_MAX_FBS) {
> +		disp_info = &p_dec_info->dec_out_info[disp_idx];

I could not reproduce the crash, it probably depends on the compiler version and
compiler options. This negative index should normally generate a pointer, even
if that points to bad location. I'd like to understand how that lead to a crash.
If you have further information on this, I really like to get to the bottom on
these subjects.

Meanwhile, this fix is obviously correct, we should not do that unless we have a
valid index.

Reviewed-by: Nicolas Dufresne <nicolas.dufresne@...labora.com>

>  		if (info->index_frame_display != info->index_frame_decoded) {
>  			/*
>  			 * when index_frame_decoded < 0, and index_frame_display >= 0
> 
> ---
> base-commit: a00b3f296eac3d43328615c3113e1a74143fc67a
> change-id: 20231129-wave5-panic-82ea2d30042f
> 
> Best regards,