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Re: [PATCH] domain: Validate __copy_to_guest in VCPUOP_register_runstate_memory_area
- To: Michal Orzel <michal.orzel@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 26 Nov 2024 11:40:40 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 26 Nov 2024 10:40:52 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 26.11.2024 11:26, Michal Orzel wrote:
> For guests with paging mode external, guest_handle_okay() always returns
> success, even if the guest handle is invalid (e.g. address not in P2M).
> In VCPUOP_register_runstate_memory_area, we would then blindly set
> runstate_guest() for a given vCPU to invalid handle. Moreover, we don't
> check the return value from __copy_to_guest() and return success to the
> guest, even in case of a failure during copy.
I'm afraid this is all deliberate, providing best effort behavior. For a
paging mode external guest, the handle may become valid subsequently. If
any __copy_to_guest() fail here, subsequent update_runstate_area() may
succeed (and success of the actual copying isn't checked there either).
> Fix it, by checking the
> return value from __copy_to_guest() and set runstate_guest() only on
> success.
_If_ such a change was wanted (despite its potential for regressions,
as guests may leverage present behavior to establish handles before
putting in place mappings), x86'es compat_vcpu_op() would need updating,
too. Plus what about VCPUOP_register_vcpu_time_memory_area, behaving
similarly?
Jan
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