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

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Date:   Wed, 14 Sep 2016 09:29:41 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Borislav Petkov <bp@...en8.de>
CC:     <linux-arch@...r.kernel.org>, <linux-efi@...r.kernel.org>,
        <kvm@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
        <kasan-dev@...glegroups.com>, <linux-mm@...ck.org>,
        <iommu@...ts.linux-foundation.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Joerg Roedel <joro@...tes.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Alexander Potapenko <glider@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [RFC PATCH v2 19/20] x86: Access the setup data through debugfs
 un-encrypted

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@....com>
>> ---
>>  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

>