linux-kernel - Re: [PATCH][next] cgroup: Avoid -Wstringop-overflow warnings

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Message-ID: <e1c07dd0-e6bf-ca9c-107a-97c5043b1bc7@embeddedor.com>
Date:   Tue, 15 Aug 2023 13:04:32 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>
Cc:     cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] cgroup: Avoid -Wstringop-overflow warnings

Hi all,

I wonder if you have any suggestions on how to address this issue. As it seems that
my last attempt caused some boot failures[1][2].

At first, I thought that the right way to fix this was through a similar fix as this
one[3]. But it seems I'm missing something else that I cannot determine yet.

These -Wstringop-overflow warnings are mostly the last ones remaining before we can
finally enable this compiler option, globally.

Any help or advice on how to properly address this is greatly appreciated. :)

Thanks!
--
Gustavo

[1] https://lore.kernel.org/linux-hardening/726aae97-755d-9806-11d4-2fb21aa93428@arm.com/
[2] https://lore.kernel.org/linux-hardening/361c2f87-1424-f452-912f-0e4a339f5c46@kernel.org/
[3] https://git.kernel.org/linus/d20d30ebb199


On 6/14/23 19:18, Gustavo A. R. Silva wrote:
> Address the following -Wstringop-overflow warnings seen when
> built with ARM architecture and aspeed_g4_defconfig configuration
> (notice that under this configuration CGROUP_SUBSYS_COUNT == 0):
> kernel/cgroup/cgroup.c:1208:16: warning: 'find_existing_css_set' accessing 4 bytes in a region of size 0 [-Wstringop-overflow=]
> kernel/cgroup/cgroup.c:1258:15: warning: 'css_set_hash' accessing 4 bytes in a region of size 0 [-Wstringop-overflow=]
> kernel/cgroup/cgroup.c:6089:18: warning: 'css_set_hash' accessing 4 bytes in a region of size 0 [-Wstringop-overflow=]
> kernel/cgroup/cgroup.c:6153:18: warning: 'css_set_hash' accessing 4 bytes in a region of size 0 [-Wstringop-overflow=]
> 
> These changes are based on commit d20d30ebb199 ("cgroup: Avoid compiler
> warnings with no subsystems").
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
>   kernel/cgroup/cgroup.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> index cd497b90e11a..1ee76e62eb98 100644
> --- a/kernel/cgroup/cgroup.c
> +++ b/kernel/cgroup/cgroup.c
> @@ -1200,6 +1200,9 @@ static struct css_set *find_css_set(struct css_set *old_cset,
>   	unsigned long key;
>   	int ssid;
>   
> +	if (!CGROUP_HAS_SUBSYS_CONFIG)
> +		return NULL;
> +
>   	lockdep_assert_held(&cgroup_mutex);
>   
>   	/* First see if we already have a cgroup group that matches
> @@ -6045,6 +6048,9 @@ int __init cgroup_init(void)
>   	struct cgroup_subsys *ss;
>   	int ssid;
>   
> +	if (!CGROUP_HAS_SUBSYS_CONFIG)
> +		return -EINVAL;
> +
>   	BUILD_BUG_ON(CGROUP_SUBSYS_COUNT > 16);
>   	BUG_ON(cgroup_init_cftypes(NULL, cgroup_base_files));
>   	BUG_ON(cgroup_init_cftypes(NULL, cgroup_psi_files));