Re: announcing LLpatch: arch-independent live-patch creation

["Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>]

On 8/26/21 5:34 PM, Peter Swain wrote:
> We have a new userspace live-patch creation tool, LLpatch, paralleling
> kpatch-build, but without requiring its arch-specific code for ELF
> analysis and manipulation.
> 
> We considered extending kpatch-build to a new target architecture
> (arm64), cluttering its code with details of another architecture’s
> quirky instruction sequences & relocation modes, and suspected there
> might be a better way.
> 
> 
> The LLVM suite already knows these details, and offers llvm-diff, for
> comparing generated code at the LLVM-IR (internal representation)
> level, which has access to much more of the code’s _intent_ than
> kpatch’s create-diff-object is able to infer from ELF-level
> differences.
> 
> 
> Building on this, LLpatch adds namespace analysis, further
> dead/duplicate code elimination, and creation of patch modules
> compatible with kernel’s livepatch API.
> 
> Arm64 is supported - testing against a livepatch-capable v5.12 arm64
> kernel, using the preliminary reliable-stacktrace work from
> madvenka@linux.microsoft.com, LLpatch modules for x86 and arm64 behave
> identically to the x86 kpatch-build modules, without requiring any
> additional arch-specific code.
> 
> On x86, where both tools are available, LLpatch produces smaller patch
> modules than kpatch, and already correctly handles most of the kpatch
> test cases, without any arch-specific code. This suggests it can work
> with any clang-supported kernel architecture.
> 
> 
> Work is ongoing, collaboration is welcome.
> 
> 
> See https://github.com/google/LLpatch for further details on the
> technology and its benefits.
> 
> 
> Yonghyun Hwang (yonghyun@google.com freeaion@gmail.com)
> Bill Wendling (morbo@google.com isanbard@gmail.com)
> Pete Swain (swine@google.com swine@pobox.com)
> 

This is great.

I have implemented an alternative method in objtool to do stack
validation for livepatch purposes. I have successfully built a livepatch
kernel and tested it. I have run all the livepatch tests in the
linux kernel sources successfully.

But I needed kpatch (or something similar) to do more testing. From Josh,
I came to know that a port to ARM64 exists for kpatch. But I was not sure
how well ARM64 was supported.

Since your tool already works on ARM64, I could really use your tool for
my testing. I will study it and contact you with any questions I might
have or any help that I might need. If everything works, I can give
you a "Tested-by".

Thanks.

Madhavan