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

From: Ard Biesheuvel
Date: Tue May 28 2019 - 02:28:20 EST

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().


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@xxxxxxx>
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));
@@ -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,
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?