From: Luis Chamberlain <mcgrof@kernel.org>
To: Joey Jiao <quic_jiangenj@quicinc.com>
Cc: linux-modules@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4] module: Add CONFIG_MODULE_DISABLE_INIT_FREE option
Date: Thu, 12 Oct 2023 09:56:18 -0700 [thread overview]
Message-ID: <ZSglMlKdvhpNq2Vy@bombadil.infradead.org> (raw)
In-Reply-To: <20231012014720.19748-1-quic_jiangenj@quicinc.com>
On Thu, Oct 12, 2023 at 07:17:19AM +0530, Joey Jiao wrote:
>
> +config MODULE_DISABLE_INIT_FREE
> + bool "Disable freeing of init sections"
> + default n
> + help
> + By default, kernel will free init sections after module being fully
> + loaded.
> +
> + MODULE_DISABLE_INIT_FREE allows users to prevent the freeing of init
> + sections. This option is particularly helpful for syzkaller fuzzing,
> + ensuring that the module consistently loads into the same address
> + across reboots.
How and why does not free'ing init help with syzkaller exactly? I don't
see the relationship between not free'ing init and ensuring th emodule
loads into the same address. There could be many things which could
incur an address gets allocated from a module at another location which
a module can take. I cannot fathom how this simple toggle could ensure
modules following the address allocations accross reboots. That seems
like odd chance, not something actually deterministic.
> +
> endif # MODULES
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index 98fedfdb8db5..0f242b7b29fe 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -2593,7 +2593,8 @@ static noinline int do_init_module(struct module *mod)
> * be cleaned up needs to sync with the queued work - ie
> * rcu_barrier()
> */
> - if (llist_add(&freeinit->node, &init_free_list))
> + if (llist_add(&freeinit->node, &init_free_list) &&
> + !IS_ENABLED(CONFIG_MODULE_DISABLE_INIT_FREE))
> schedule_work(&init_free_wq);
prev parent reply other threads:[~2023-10-12 16:56 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-12 1:47 [PATCH v4] module: Add CONFIG_MODULE_DISABLE_INIT_FREE option Joey Jiao
2023-10-12 16:56 ` Luis Chamberlain [this message]
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