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authorKirill A. Shutemov <kirill.shutemov@linux.intel.com>2023-01-27 01:11:59 +0300
committerDave Hansen <dave.hansen@linux.intel.com>2023-01-27 20:46:05 +0300
commit8de62af018cc9262649d7688f7eb1409b2d8f594 (patch)
treefb40e473c0c8bb06b4bb753316e363a9dbf9e2e6 /arch/x86/coco
parent47e67cf317ed6ad22a3df9762daae75dfcba76a8 (diff)
downloadlinux-8de62af018cc9262649d7688f7eb1409b2d8f594.tar.xz
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
Diffstat (limited to 'arch/x86/coco')
-rw-r--r--arch/x86/coco/tdx/tdx.c7
1 files changed, 7 insertions, 0 deletions
diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index c4a1299a0691..b593009b30ab 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.