Re: [Xen-devel] [PATCH for-4.12] x86/p2m: Drop erroneous #VE-enabled check in ept_set_entry()

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 1/24/19 8:28 PM, Andrew Cooper wrote:
> Code clearing the "Suppress VE" bit in an EPT entry isn't nececsserily running
> in current context.  In ALTP2M_external mode, it definitely is not, and in PV
> context, vcpu_altp2m(current) acts upon the HVM union.
> 
> Even if we could sensibly resolve the target vCPU, it may legitimately not be
> fully set up at this point, so rejecting the EPT modification would be buggy.
> 
> There is a path in hvm_hap_nested_page_fault() which explicitly emulates #VE
> in the cpu_has_vmx_virt_exceptions case, so the -EOPNOTSUPP part of this
> condition is also wrong.
> 
> Drop the !sve check entirely.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> CC: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
> CC: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
> CC: Jun Nakajima <jun.nakajima@xxxxxxxxx>
> CC: Kevin Tian <kevin.tian@xxxxxxxxx>
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> CC: Juergen Gross <jgross@xxxxxxxx>
> 
> Discovered while trying to fix the gaping security hole with ballooning out
> the #VE info page.  The risk for 4.12 is very minimal - altp2m is off by
> default, not security supported, and the ability to clearing sve is limited to
> introspection code paths.

Reviewed-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>


Thanks,
Razvan

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel