Re: [Xen-devel] [PATCH v1 3/6] x86: Enable Supervisor Mode Execution Prevention (SMAP) for Xen

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 15/04/14 15:00, Andrew Cooper wrote:
> On 15/04/14 14:01, Feng Wu wrote:
>> @@ -1379,8 +1396,8 @@ void do_page_fault(struct cpu_user_regs *regs)
>>  
>>      if ( unlikely(!guest_mode(regs)) )
>>      {
>> -        pf_type = spurious_page_fault(addr, error_code);
>> -        BUG_ON(pf_type == smep_fault);
>> +        pf_type = spurious_page_fault(addr, regs);
>> +        BUG_ON((pf_type == smep_fault) || (pf_type == smap_fault));
> On further consideration, given the nature of faults like these, this
> code would be better as:
>
> if ( (pf_type == smep_fault) || (pf_type == smap_fault) )
> {
>     console_start_sync();
>     printk("Xen SM%cP violation", pf_type == smep_fault ? 'E' : 'A');
>     fatal_trap(TRAP_page_fault, regs);
> }
>
> This would make the resulting crash crystal clear as to what went wrong,
> and forgo the first step of having to look up which BUG() tripped.
>
> ~Andrew

And having just sent this email, I further realise that functions like
show_page_walk() need protection against SMAP otherwise we will take a
recursive fault when trying to dump the error information from the first
fault.  I don't recall any of your other patches dealing with this.

All this error printing can probably better be colated together after
the exception table search.

~Andrew

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