linux-kernel - Re: [PATCH 05/13] media: mgb4: protect driver against spectre

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <97cdc438-5699-4ab5-8c18-5fe39fe7e101@gpxsee.org>
Date: Fri, 18 Oct 2024 13:21:33 +0200
From: Martin Tůma <tumic@...see.org>
To: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Cc: Hans Verkuil <hverkuil@...all.nl>,
 Martin Tuma <martin.tuma@...iteqautomotive.com>,
 linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
 stable@...r.kernel.org
Subject: Re: [PATCH 05/13] media: mgb4: protect driver against spectre

Hi,

On 18. 10. 24 6:32 dop., Mauro Carvalho Chehab wrote:
> Em Wed, 16 Oct 2024 13:59:18 +0200
> Martin Tůma <tumic@...see.org> escreveu:
> 
>> On 16. 10. 24 12:22 odp., Mauro Carvalho Chehab wrote:
>>> Frequency range is set from sysfs via frequency_range_store(),
>>> being vulnerable to spectre, as reported by smatch:
>>>
>>> 	drivers/media/pci/mgb4/mgb4_cmt.c:231 mgb4_cmt_set_vin_freq_range() warn: potential spectre issue 'cmt_vals_in' [r]
>>> 	drivers/media/pci/mgb4/mgb4_cmt.c:238 mgb4_cmt_set_vin_freq_range() warn: possible spectre second half.  'reg_set'
>>>
>>> Fix it.
>>>
>>> Fixes: 0ab13674a9bd ("media: pci: mgb4: Added Digiteq Automotive MGB4 driver")
>>> Cc: stable@...r.kernel.org
>>> Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
>>> ---
>>>    drivers/media/pci/mgb4/mgb4_cmt.c | 2 ++
>>>    1 file changed, 2 insertions(+)
>>>
>>> diff --git a/drivers/media/pci/mgb4/mgb4_cmt.c b/drivers/media/pci/mgb4/mgb4_cmt.c
>>> index 70dc78ef193c..a25b68403bc6 100644
>>> --- a/drivers/media/pci/mgb4/mgb4_cmt.c
>>> +++ b/drivers/media/pci/mgb4/mgb4_cmt.c
>>> @@ -227,6 +227,8 @@ void mgb4_cmt_set_vin_freq_range(struct mgb4_vin_dev *vindev,
>>>    	u32 config;
>>>    	size_t i;
>>>    
>>> +	freq_range = array_index_nospec(freq_range, ARRAY_SIZE(cmt_vals_in));
>>> +
>>>    	addr = cmt_addrs_in[vindev->config->id];
>>>    	reg_set = cmt_vals_in[freq_range];
>>>      
>>
>> I still do not fully understand the exact vulnerability here, but the
>> patch should definitely not do any harm, so I'm ok with it even if it's
>> real purpose would only be to silence the smatch warning :-)
> 
> With Spectre, just checking if freq_range is between 0 and the
> size of the array is not enough, as malicious code could use CPU
> speculative logic to retrieve data from memory outside the limits
> of the array.
> 
> As freq_range is specified by the user via sysfs attribute
> frequency_range, it is subject to Spectre v1 attack as described
> at Documentation/admin-guide/hw-vuln/spectre.rst.
> 

I do know the general theory about the "spectre bounds check 
fix/workaround", what I was referring is this part in the documentation:

"Such speculative memory accesses can leave side effects, creating side 
channels which leak information to the attacker."

I do not see/understand the exact "information leak" that could happen 
here on this particular place. But as already stated in the original 
answer, I don't have to understand everything ;-)

M.

> Silencing smatch is a plus.
> 
>>
>> Reviewed-by: Martin Tůma <martin.tuma@...iteqautomotive.com>
> 
> Thanks!
> 
> Thanks,
> Mauro
>