On 19.04.22 16:37, Andrew Cooper wrote:
On 19/04/2022 14:52, Juergen Gross wrote:A hypervisor built without CONFIG_GDBSX will crash in case the XEN_DOMCTL_gdbsx_guestmemio domctl is being called, as the call will end up in iommu_do_domctl() with d == NULL:(XEN) CPU: 6 (XEN) RIP: e008:[<ffff82d040269984>] iommu_do_domctl+0x4/0x30 (XEN) RFLAGS: 0000000000010202 CONTEXT: hypervisor (d0v0) (XEN) rax: 00000000000003e8 rbx: ffff830856277ef8 rcx: ffff830856277fff ... (XEN) Xen call trace: (XEN) [<ffff82d040269984>] R iommu_do_domctl+0x4/0x30 (XEN) [<ffff82d04035cd5f>] S arch_do_domctl+0x7f/0x2330 (XEN) [<ffff82d040239e46>] S do_domctl+0xe56/0x1930 (XEN) [<ffff82d040238ff0>] S do_domctl+0/0x1930 (XEN) [<ffff82d0402f8c59>] S pv_hypercall+0x99/0x110 (XEN) [<ffff82d0402f5161>] S arch/x86/pv/domain.c#_toggle_guest_pt+0x11/0x90 (XEN) [<ffff82d040366288>] S lstar_enter+0x128/0x130 (XEN) (XEN) Pagetable walk from 0000000000000144: (XEN) L4[0x000] = 0000000000000000 ffffffffffffffff (XEN) (XEN) **************************************** (XEN) Panic on CPU 6: (XEN) FATAL PAGE FAULT (XEN) [error_code=0000] (XEN) Faulting linear address: 0000000000000144 Fix this issue by making sure the domain pointer has a sane value. Reported-by: Cheyenne Wills <[email protected]> Fixes: e726a82ca0dc ("xen: make gdbsx support configurable") Signed-off-by: Juergen Gross <[email protected]>Thanks, but I was hoping for a bit of discussion on the use of DOMID_IDLE. It used to be permitted to pass DOMID_IDLE to dbg_rw_mem() to access Xen memory, which is why the XEN_DOMCTL_gdbsx_guestmemio special case existed. It turns out that it was also e726a82ca0dc which dropped the ability to use DOMID_IDLE, meaning that this fix is a missing hunk from the original change too. This is relevant backport information, and would have created complexities if they hadn't been the same changeset. So, now about: "It used to be permitted to pass DOMID_IDLE to dbg_rw_mem(), which is why the special case excluding domid checks exists. Now that it is only permitted to pass proper domids, remove the special case, thus making 'd' always valid." ?
Fine with me.
Can be fixed on commit, so Reviewed-by: Andrew Cooper <[email protected]> for everything else.
Thanks, Juergen
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