Avi Kivity wrote:
> On 05/26/2010 05:46 AM, Xiao Guangrong wrote:
>> There is a relaxing permission operation in set_spte():
>>
>> if guest's CR0.WP is not set and R/W #PF occurs in supervisor-level,
>> the mapping path might set to writable, then user can allow to write.
>>
>> @@ -1859,8 +1859,7 @@ static int set_spte(struct kvm_vcpu *vcpu, u64
>> *sptep,
>>
>> spte |= (u64)pfn<< PAGE_SHIFT;
>>
>> - if ((pte_access& ACC_WRITE_MASK)
>> - || (write_fault&& !is_write_protection(vcpu)&& !user_fault)) {
>> + if (pte_access& ACC_WRITE_MASK) {
>>
>>
>
> The host always sets cr0.wp (in shadow mode) so we can write protect
> page tables. So when the guest clears cr0.wp, we emulate a gpte with
> gpte.w=0 and gpte.u=1 in two ways:
>
> - spte.w=1, spte.u=0: this will allow the guest kernel to write but trap
> on guest user access
> - spte.w=0, spte.u=1: allows guest user access but traps on guest kernel
> writes
>
> If the guest attempts an access that is currently disallowed, we switch
> to the other spte encoding.
Avi,
Thanks for your explanation, but i not see where to implement what you say,
could you please point it out for me? :-(
And, i think use 'spte.w=1, spte.u=0' to emulate 'guest cr0.wp=0 and gpte.w=0'
is not a good way since it can completely stop user process access, but in this
case, user process is usually read and kernel lazily to write, just like vdso,
it will generate a lots of #PF
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