On Tue, 2017-05-16 at 19:11 +0530, Naveen N. Rao wrote:

On 2017/05/16 10:56AM, Anshuman Khandual wrote:

quoted

On 05/16/2017 09:19 AM, Balbir Singh wrote:

quoted

patch_instruction is enhanced in this RFC to support
patching via a different virtual address (text_poke_area).

Why writing instruction directly into the address is not
sufficient and need to go through this virtual address ?

To enable KERNEL_STRICT_RWX and map all of kernel text to be read-only?

Precisely, the rest of the bits are still being developed.
 

quoted

quoted

The mapping of text_poke_area->addr is RW and not RWX.
This way the mapping allows write for patching and then we tear
down the mapping. The downside is that we introduce a spinlock
which serializes our patching to one patch at a time.

So whats the benifits we get otherwise in this approach when
we are adding a new lock into the equation.

Instruction patching isn't performance critical, so the slow down is 
likely not noticeable. Marking kernel text read-only helps harden the 
kernel by catching unintended code modifications whether through 
exploits or through bugs.

Precisely!

Balbir Singh.