On Tue, Sep 03, 2024 at 06:49:46PM +0100, Lorenzo Stoakes wrote:

On Mon, Sep 02, 2024 at 08:08:15PM GMT, Mark Brown wrote:

quoted

On x86 there is a custom arch_get_unmapped_area() which was updated by the
above commit to cover this case by specifying a start_gap for allocations
with VM_SHADOW_STACK. Both arm64 and RISC-V have equivalent features and
use the generic implementation of arch_get_unmapped_area() so let's make
the equivalent change there so they also don't get shadow stack pages
placed without guard pages.

Don't you need to unwind that change in x86 now you're doing it in generic code?

No, x86 had a preexisting custom implementation for some other reason
(hence the "updated by the above commit" part above) - the shadow stack
support would most likely have been added in the core in the first place
were it not for that.