Re: [PATCH v7 24/41] mm: Don't allow write GUPs to shadow stack memory

On Mon, Mar 6, 2023 at 5:10 AM Borislav Petkov [off-list ref] wrote:

On Mon, Feb 27, 2023 at 02:29:40PM -0800, Rick Edgecombe wrote:

quoted

The x86 Control-flow Enforcement Technology (CET) feature includes a new
type of memory called shadow stack. This shadow stack memory has some
unusual properties, which requires some core mm changes to function
properly.

Shadow stack memory is writable only in very specific, controlled ways.
However, since it is writable, the kernel treats it as such. As a result

                                                                          ^
                                                                          ,

quoted

there remain many ways for userspace to trigger the kernel to write to
shadow stack's via get_user_pages(, FOLL_WRITE) operations. To make this a

Is there an alternate mechanism, or do we still want to allow
FOLL_FORCE so that debuggers can write it?

--Andy