linux-kernel - Re: [PATCH 1/4] arm64: module: create module allocations without exec permissions

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Date:   Tue, 28 May 2019 08:24:50 +0200
From:   Ard Biesheuvel <ard.biesheuvel@....com>
To:     Anshuman Khandual <anshuman.khandual@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     mark.rutland@....com, marc.zyngier@....com,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Nadav Amit <namit@...are.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        James Morse <james.morse@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>
Subject: Re: [PATCH 1/4] arm64: module: create module allocations without exec
 permissions

On 5/28/19 7:35 AM, Anshuman Khandual wrote:
> 
> 
> On 05/23/2019 03:52 PM, Ard Biesheuvel wrote:
>> Now that the core code manages the executable permissions of code
>> regions of modules explicitly, it is no longer necessary to create
> 
> I guess the permission transition for various module sections happen
> through module_enable_[ro|nx]() after allocating via module_alloc().
> 

Indeed.

>> the module vmalloc regions with RWX permissions, and we can create
>> them with RW- permissions instead, which is preferred from a
>> security perspective.
> 
> Makes sense. Will this be followed in all architectures now ?
> 

I am not sure if every architecture implements module_enable_[ro|nx](), 
but if they do, they should probably apply this change as well.

>>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@....com>
>> ---
>>   arch/arm64/kernel/module.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm64/kernel/module.c b/arch/arm64/kernel/module.c
>> index 2e4e3915b4d0..88f0ed31d9aa 100644
>> --- a/arch/arm64/kernel/module.c
>> +++ b/arch/arm64/kernel/module.c
>> @@ -41,7 +41,7 @@ void *module_alloc(unsigned long size)
>>   
>>   	p = __vmalloc_node_range(size, MODULE_ALIGN, module_alloc_base,
>>   				module_alloc_base + MODULES_VSIZE,
>> -				gfp_mask, PAGE_KERNEL_EXEC, 0,
>> +				gfp_mask, PAGE_KERNEL, 0,
>>   				NUMA_NO_NODE, __builtin_return_address(0));
>>   
>>   	if (!p && IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) &&
>> @@ -57,7 +57,7 @@ void *module_alloc(unsigned long size)
>>   		 */
>>   		p = __vmalloc_node_range(size, MODULE_ALIGN, module_alloc_base,
>>   				module_alloc_base + SZ_4G, GFP_KERNEL,
>> -				PAGE_KERNEL_EXEC, 0, NUMA_NO_NODE,
>> +				PAGE_KERNEL, 0, NUMA_NO_NODE,
>>   				__builtin_return_address(0));
>>   
>>   	if (p && (kasan_module_alloc(p, size) < 0)) {
>>
> 
> Which just makes sure that PTE_PXN never gets dropped while creating
> these mappings.
> 

Not sure what you mean. Is there a question here?