Messages in this thread | | | Date | Fri, 9 Dec 2022 20:10:29 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCH 4/4] x86/tdx: Disable NOTIFY_ENABLES |
| |
On Fri, Dec 09, 2022 at 07:50:46AM -0800, Sathyanarayanan Kuppuswamy wrote: > > > On 12/9/22 5:25 AM, Kirill A. Shutemov wrote: > > == Background == > > > > There is a class of side-channel attacks against SGX enclaves called > > "SGX Step"[1]. These attacks create lots of exceptions inside of > > enclaves. Basically, run an in-enclave instruction, cause an exception. > > Over and over. > > > > There is a concern that a VMM could attack a TDX guest in the same way > > by causing lots of #VE's. The TDX architecture includes new > > countermeasures for these attacks. It basically counts the number of > > exceptions and can send another *special* exception once the number of > > VMM-induced #VE's hits a critical threshold[2]. > > > > == Problem == > > > > But, these special exceptions are independent of any action that the > > guest takes. They can occur anywhere that the guest executes. This > > includes sensitive areas like the entry code. The (non-paranoid) #VE > > handler is incapable of handling exceptions in these areas. > > > > == Solution == > > > > Fortunately, the special exceptions can be disabled by the guest via > > write to NOTIFY_ENABLES TDCS field. NOTIFY_ENABLES is disabled by > > default, but might be enabled by a bootloader, firmware or an earlier > > kernel before the current kernel runs. > > > > Disable NOTIFY_ENABLES feature explicitly and unconditionally. Any > > NOTIFY_ENABLES-based #VE's that occur before this point will end up > > in the early #VE exception handler and die due to unexpected exit > > reason. > > > > [1] https://github.com/jovanbulck/sgx-step > > [2] https://intel.github.io/ccc-linux-guest-hardening-docs/security-spec.html#safety-against-ve-in-kernel-code > > > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > > --- > > I don't think you need to explicitly use section names (Background, > problem or solution) in the commit log. But it is up to you. > > Rest looks good. >
I've checked git log and some people leave them in. I've decided to keep them too.
-- Kiryl Shutsemau / Kirill A. Shutemov
| |