Re: [RFC PATCH] kernel/module: have the callers of set_memory_*() check the return value

From: Tianlin Li <tli@digitalocean.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: kernel-hardening@lists.openwall.com,
	Kees Cook <keescook@chromium.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ingo Molnar <mingo@redhat.com>,
	Russell King <linux@armlinux.org.uk>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, Greentime Hu <green.hu@gmail.com>,
	Vincent Chen <deanbo422@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Borislav Petkov <bp@alien8.de>, "H . Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org, Jessica Yu <jeyu@kernel.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Jiri Kosina <jikos@kernel.org>, Miroslav Benes <mbenes@suse.cz>,
	Petr Mladek <pmladek@suse.com>,
	Joe Lawrence <joe.lawrence@redhat.com>
Subject: Re: [RFC PATCH] kernel/module: have the callers of set_memory_*() check the return value
Date: Tue, 19 Nov 2019 15:54:44 -0600	[thread overview]
Message-ID: <16D5632C-27F1-4B9C-9255-A0B67582623D@digitalocean.com> (raw)
In-Reply-To: <20191119213854.GP3079@worktop.programming.kicks-ass.net>

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> On Nov 19, 2019, at 3:38 PM, Peter Zijlstra <peterz@infradead.org> wrote:
> 
> On Tue, Nov 19, 2019 at 09:51:49AM -0600, Tianlin Li wrote:
>> Right now several architectures allow their set_memory_*() family of 
>> functions to fail, but callers may not be checking the return values. We 
>> need to fix the callers and add the __must_check attribute. They also may
>> not provide any level of atomicity, in the sense that the memory 
>> protections may be left incomplete on failure. This issue likely has a few 
>> steps on effects architectures[1]:
>> 1)Have all callers of set_memory_*() helpers check the return value.
>> 2)Add __much_check to all set_memory_*() helpers so that new uses do not 
>> ignore the return value.
>> 3)Add atomicity to the calls so that the memory protections aren't left in 
>> a partial state.
>> 
>> Ideally, the failure of set_memory_*() should be passed up the call stack, 
>> and callers should examine the failure and deal with it. But currently, 
>> some callers just have void return type.
>> 
>> We need to fix the callers to handle the return all the way to the top of 
>> stack, and it will require a large series of patches to finish all the three 
>> steps mentioned above. I start with kernel/module, and will move onto other 
>> subsystems. I am not entirely sure about the failure modes for each caller. 
>> So I would like to get some comments before I move forward. This single 
>> patch is just for fixing the return value of set_memory_*() function in 
>> kernel/module, and also the related callers. Any feedback would be greatly 
>> appreciated.
> 
> Please have a look here:
> 
>  https://lkml.kernel.org/r/20191111131252.921588318@infradead.org <https://lkml.kernel.org/r/20191111131252.921588318@infradead.org>
> 
> Much of the code you're patching is slated for removal.
> 
> Josh also has patches reworking KLP and there's some ARM64 patches
> pending at which point we can also delete module_disable_ro().
Thanks for the information. I will check the code. 

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