linux-kernel - Re: [PATCH v3 6/9] module: switch to execmem API for remapping as RW and restoring ROX

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Message-ID: <099b8e0b-2c64-482f-8c22-32afc5b21beb@suse.com>
Date: Tue, 28 Jan 2025 11:31:36 +0100
From: Petr Pavlu <petr.pavlu@...e.com>
To: Mike Rapoport <rppt@...nel.org>
Cc: x86@...nel.org, Andrew Morton <akpm@...ux-foundation.org>,
 Andy Lutomirski <luto@...nel.org>,
 Anton Ivanov <anton.ivanov@...bridgegreys.com>,
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 "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
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 <samitolvanen@...gle.com>, Shuah Khan <shuah@...nel.org>,
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Subject: Re: [PATCH v3 6/9] module: switch to execmem API for remapping as RW
 and restoring ROX

On 1/28/25 11:00, Mike Rapoport wrote:
> On Mon, Jan 27, 2025 at 01:50:31PM +0100, Petr Pavlu wrote:
>> On 1/26/25 08:47, Mike Rapoport wrote:
>>> From: "Mike Rapoport (Microsoft)" <rppt@...nel.org>
>>>
>>> Instead of using writable copy for module text sections, temporarily remap
>>> the memory allocated from execmem's ROX cache as writable and restore its
>>> ROX permissions after the module is formed.
>>>
>>> This will allow removing nasty games with writable copy in alternatives
>>> patching on x86.
>>>
>>> Signed-off-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
>>
>> [...]
>>
>>> +static void module_memory_restore_rox(struct module *mod)
>>> +{
>>> +	for_class_mod_mem_type(type, text) {
>>> +		struct module_memory *mem = &mod->mem[type];
>>> +
>>> +		if (mem->is_rox)
>>> +			execmem_restore_rox(mem->base, mem->size);
>>> +	}
>>> +}
>>> +
>>
>> Can the execmem_restore_rox() call here fail? I realize that there isn't
>> much that the module loader can do if that happens, but should it be
>> perhaps logged as a warning?
> 
> It won't fail at this point. set_memory APIs may fail if they need to split
> a large page and could not allocate a new page table, but here all the
> splits were already done at module_memory_alloc() time.

Ok, thanks for the explanation.

Acked-by: Petr Pavlu <petr.pavlu@...e.com>

-- Petr