Re: [PATCH v2 01/10] mm: add Kernel Electric-Fence infrastructure

[Marco Elver <elver@google.com>]

On Thu, 17 Sep 2020 at 15:26, Hillf Danton <hdanton@sina.com> wrote:
>
>
> Tue, 15 Sep 2020 15:20:37 +0200
> > From: Alexander Potapenko <glider@google.com>
> >
> > This adds the Kernel Electric-Fence (KFENCE) infrastructure. KFENCE is a
> > low-overhead sampling-based memory safety error detector of heap
> > use-after-free, invalid-free, and out-of-bounds access errors.
> >
> > KFENCE is designed to be enabled in production kernels, and has near
> > zero performance overhead. Compared to KASAN, KFENCE trades performance
> > for precision. The main motivation behind KFENCE's design, is that with
> > enough total uptime KFENCE will detect bugs in code paths not typically
> > exercised by non-production test workloads. One way to quickly achieve a
> > large enough total uptime is when the tool is deployed across a large
> > fleet of machines.
> >
> > KFENCE objects each reside on a dedicated page, at either the left or
> > right page boundaries. The pages to the left and right of the object
> > page are "guard pages", whose attributes are changed to a protected
> > state, and cause page faults on any attempted access to them. Such page
> > faults are then intercepted by KFENCE, which handles the fault
> > gracefully by reporting a memory access error.
>
> To help understand the magic of KFENCE, a simple diagram looks needed to
> illustrate the relations between obj and guard pages, something like the
> below asiic chart.
>
>         |-----------------|-----------------------------------|------------------|
>         | left guard page | the page containing KFENCE object | right guard page |
>         |-----------------|-----------------------------------|------------------|
>

Would the one we have in Documentation be what you're after?

https://lore.kernel.org/linux-arm-kernel/20200915132046.3332537-10-elver@google.com/
(at "The following figure illustrates the page layout::")

Let us know if you'd like that copied into the commit message.

Thanks,
-- Marco