Re: [RFC PATCH v2 19/20] x86: Access the setup data through debugfs un-encrypted

[Tom Lendacky]

On 09/12/2016 11:59 AM, Borislav Petkov wrote:
> On Mon, Aug 22, 2016 at 05:38:59PM -0500, Tom Lendacky wrote:
>> Since the setup data is in memory in the clear, it must be accessed as
>> un-encrypted.  Always use ioremap (similar to sysfs setup data support)
>> to map the data.
>>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
>> ---
>>  arch/x86/kernel/kdebugfs.c |   30 +++++++++++-------------------
>>  1 file changed, 11 insertions(+), 19 deletions(-)
>>
>> diff --git a/arch/x86/kernel/kdebugfs.c b/arch/x86/kernel/kdebugfs.c
>> index bdb83e4..a58a82e 100644
>> --- a/arch/x86/kernel/kdebugfs.c
>> +++ b/arch/x86/kernel/kdebugfs.c
>> @@ -48,17 +48,13 @@ static ssize_t setup_data_read(struct file *file, char __user *user_buf,
>>  
>>  	pa = node->paddr + sizeof(struct setup_data) + pos;
>>  	pg = pfn_to_page((pa + count - 1) >> PAGE_SHIFT);
>> -	if (PageHighMem(pg)) {
> 
> Why is it ok to get rid of the PageHighMem() check?

Since the change is to perform the ioremap call no matter what the check
for PageHighMem() wasn't needed anymore.

> 
> Btw, we did talk earlier in the thread about making __va() clear the SME
> mask and then you won't really need to change stuff here. Or?

This is still required because just using the __va() would still cause
the mapping created to have the encryption bit set. The ioremap call
will result in the mapping not having the encryption bit set.

Thanks,
Tom

>