Re: [PATCH] mshv: Fix infinite fault loop on permission-denied GPA intercepts

[Anirudh Rayabharam <anirudh@anirudhrb.com>]

On Tue, Mar 24, 2026 at 11:57:40PM +0000, Stanislav Kinsburskii wrote:
> Prevent infinite fault loops when guests access memory regions without
> proper permissions. Currently, mshv_handle_gpa_intercept() attempts to
> remap pages for all faults on movable memory regions, regardless of
> whether the access type is permitted. When a guest writes to a read-only
> region, the remap succeeds but the region remains read-only, causing
> immediate re-fault and spinning the vCPU indefinitely.
> 
> Validate intercept access type against region permissions before
> attempting remaps. Reject writes to non-writable regions and executes to
> non-executable regions early, returning false to let the VMM handle the
> intercept appropriately.
> 
> This also closes a potential DoS vector where malicious guests could
> intentionally trigger these fault loops to consume host resources.
> 
> Fixes: b9a66cd5ccbb ("mshv: Add support for movable memory regions")
> Signed-off-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
> ---
>  drivers/hv/mshv_root_main.c |   15 ++++++++++++---
>  include/hyperv/hvgdk_mini.h |    6 ++++++
>  include/hyperv/hvhdk.h      |    4 ++--
>  3 files changed, 20 insertions(+), 5 deletions(-)

Reviewed-by: Anirudh Rayabharam (Microsoft) <anirudh@anirudhrb.com>