From: Dave Hansen <dave.hansen@intel.com>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>
Cc: Kuppuswamy Sathyanarayanan
<sathyanarayanan.kuppuswamy@linux.intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Elena Reshetova <elena.reshetova@intel.com>,
x86@kernel.org, linux-coco@lists.linux.dev,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/4] x86/tdx: Disable NOTIFY_ENABLES
Date: Tue, 13 Dec 2022 15:17:02 -0800 [thread overview]
Message-ID: <6eed73b1-adee-caf7-e02f-4d2b08f1aefe@intel.com> (raw)
In-Reply-To: <20221209132524.20200-5-kirill.shutemov@linux.intel.com>
On 12/9/22 05:25, 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>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
prev parent reply other threads:[~2022-12-13 23:17 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-09 13:25 [PATCH 0/4] x86/tdx: Changes for TDX guest initialization Kirill A. Shutemov
2022-12-09 13:25 ` [PATCH 1/4] x86/tdx: Expand __tdx_hypercall() to handle more arguments Kirill A. Shutemov
2022-12-13 22:44 ` Dave Hansen
2022-12-09 13:25 ` [PATCH 2/4] x86/tdx: Use ReportFatalError to report missing SEPT_VE_DISABLE Kirill A. Shutemov
2022-12-09 15:42 ` Sathyanarayanan Kuppuswamy
2022-12-09 17:06 ` Kirill A. Shutemov
2022-12-09 20:51 ` Sathyanarayanan Kuppuswamy
2022-12-12 16:10 ` Dave Hansen
2022-12-12 16:37 ` Sathyanarayanan Kuppuswamy
2022-12-12 16:39 ` Dave Hansen
2022-12-13 23:06 ` Dave Hansen
2022-12-15 17:12 ` Kirill A. Shutemov
2022-12-15 18:18 ` Dave Hansen
2022-12-15 18:51 ` Kirill A. Shutemov
2022-12-15 21:09 ` Dave Hansen
2022-12-16 2:38 ` Kirill A. Shutemov
2022-12-16 15:22 ` Reshetova, Elena
2022-12-09 13:25 ` [PATCH 3/4] x86/tdx: Relax SEPT_VE_DISABLE check for debug TD Kirill A. Shutemov
2022-12-09 15:45 ` Sathyanarayanan Kuppuswamy
2022-12-09 17:08 ` Kirill A. Shutemov
2022-12-13 23:13 ` Dave Hansen
2022-12-15 15:40 ` Kirill A. Shutemov
2022-12-09 13:25 ` [PATCH 4/4] x86/tdx: Disable NOTIFY_ENABLES Kirill A. Shutemov
2022-12-09 15:50 ` Sathyanarayanan Kuppuswamy
2022-12-09 17:10 ` Kirill A. Shutemov
2022-12-13 23:17 ` Dave Hansen [this message]
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