From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To: Dave Hansen <dave.hansen@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,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: [PATCH 4/4] x86/tdx: Disable NOTIFY_ENABLES
Date: Fri, 9 Dec 2022 16:25:24 +0300 [thread overview]
Message-ID: <20221209132524.20200-5-kirill.shutemov@linux.intel.com> (raw)
In-Reply-To: <20221209132524.20200-1-kirill.shutemov@linux.intel.com>
== 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>
---
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 0e47846ff8ff..c93c2fd2e113 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
@@ -858,6 +862,9 @@ 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.
--
2.38.0
next prev parent reply other threads:[~2022-12-09 13:25 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 ` Kirill A. Shutemov [this message]
2022-12-09 15:50 ` [PATCH 4/4] x86/tdx: Disable NOTIFY_ENABLES Sathyanarayanan Kuppuswamy
2022-12-09 17:10 ` Kirill A. Shutemov
2022-12-13 23:17 ` Dave Hansen
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20221209132524.20200-5-kirill.shutemov@linux.intel.com \
--to=kirill.shutemov@linux.intel.com \
--cc=bp@alien8.de \
--cc=dave.hansen@intel.com \
--cc=elena.reshetova@intel.com \
--cc=linux-coco@lists.linux.dev \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@kernel.org \
--cc=sathyanarayanan.kuppuswamy@linux.intel.com \
--cc=tglx@linutronix.de \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).