Re: [Xen-devel] [PATCH] x86/HVM: correct notion of new CPL in task switch emulation

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 05.06.17 at 15:06, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 01/06/17 13:11, Jan Beulich wrote:
>> Commit aac1df3d03 ("x86/HVM: introduce hvm_get_cpl() and respective
>> hook") went too far in one aspect: When emulating a task switch we
>> really shouldn't be looking at what hvm_get_cpl() returns, as we're
>> switching all segment registers.
>>
>> However, instead of reverting the relevant parts of that commit, have
>> the caller tell the segment loading function what the new CPL is. This
>> at once fixes ES being loaded before CS so far having had its checks
>> done against the old CPL.
>>
>> Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> On further consideration, wouldn't it be better to audit all segment
> registers, before updating any of them in the vmcs/vmcb?  This would
> leave us with a far lower chance of other vmentry failures.

Overall yes (and I did make a not on my todo list), but I think we
want to address the regression with no meaningful re-work right
now.

Jan



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