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Shutemov" <tip-bot2@linutronix.de> Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: x86/tdx] x86/tdx: Disable NOTIFY_ENABLES Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Dave Hansen <dave.hansen@linux.intel.com>, Dave Hansen <dave.hansen@intel.com>, x86@kernel.org, linux-kernel@vger.kernel.org MIME-Version: 1.0 Message-ID: <167484401546.4906.1415806415892666642.tip-bot2@tip-bot2> Robot-ID: <tip-bot2@linutronix.de> Robot-Unsubscribe: Contact <mailto:tglx@linutronix.de> to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-4.4 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_MED,SPF_HELO_NONE, SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: <linux-kernel.vger.kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1756201431334664176?= X-GMAIL-MSGID: =?utf-8?q?1756201431334664176?= |
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[tip:,x86/tdx] x86/tdx: Disable NOTIFY_ENABLES
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Commit Message
tip-bot2 for Thomas Gleixner
Jan. 27, 2023, 6:26 p.m. UTC
The following commit has been merged into the x86/tdx branch of tip: Commit-ID: 8de62af018cc9262649d7688f7eb1409b2d8f594 Gitweb: https://git.kernel.org/tip/8de62af018cc9262649d7688f7eb1409b2d8f594 Author: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> AuthorDate: Fri, 27 Jan 2023 01:11:59 +03:00 Committer: Dave Hansen <dave.hansen@linux.intel.com> CommitterDate: Fri, 27 Jan 2023 09:46:05 -08:00 x86/tdx: Disable NOTIFY_ENABLES == 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> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Reviewed-by: Dave Hansen <dave.hansen@intel.com> Link: https://lore.kernel.org/all/20230126221159.8635-8-kirill.shutemov%40linux.intel.com --- arch/x86/coco/tdx/tdx.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c index c4a1299..b593009 100644 --- a/arch/x86/coco/tdx/tdx.c +++ b/arch/x86/coco/tdx/tdx.c @@ -19,6 +19,10 @@ #define TDX_GET_VEINFO 3 #define TDX_GET_REPORT 4 #define TDX_ACCEPT_PAGE 6 +#define TDX_WR 8 + +/* TDCS fields. To be used by TDG.VM.WR and TDG.VM.RD module calls */ +#define TDCS_NOTIFY_ENABLES 0x9100000000000010 /* TDX hypercall Leaf IDs */ #define TDVMCALL_MAP_GPA 0x10001 @@ -863,6 +867,9 @@ void __init tdx_early_init(void) tdx_parse_tdinfo(&cc_mask); cc_set_mask(cc_mask); + /* Kernel does not use NOTIFY_ENABLES and does not need random #VEs */ + tdx_module_call(TDX_WR, 0, TDCS_NOTIFY_ENABLES, 0, -1ULL, NULL); + /* * All bits above GPA width are reserved and kernel treats shared bit * as flag, not as part of physical address.