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SubjectRe: [PATCH 1/4] arm64: module: create module allocations without exec permissions
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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@arm.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?


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