linux-kernel - [PATCH v3 8/8] x86/virt/tdx: Don't initialize module that doesn't support NO_RBP

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Message-ID: <0996e2f1b3e5c72150708b10bff57ad726c69e4b.1724741926.git.kai.huang@intel.com>
Date: Tue, 27 Aug 2024 19:14:30 +1200
From: Kai Huang <kai.huang@...el.com>
To: dave.hansen@...el.com,
	kirill.shutemov@...ux.intel.com,
	tglx@...utronix.de,
	bp@...en8.de,
	peterz@...radead.org,
	mingo@...hat.com,
	hpa@...or.com,
	dan.j.williams@...el.com,
	seanjc@...gle.com,
	pbonzini@...hat.com
Cc: x86@...nel.org,
	linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org,
	rick.p.edgecombe@...el.com,
	isaku.yamahata@...el.com,
	chao.gao@...el.com,
	binbin.wu@...ux.intel.com,
	adrian.hunter@...el.com,
	kai.huang@...el.com
Subject: [PATCH v3 8/8] x86/virt/tdx: Don't initialize module that doesn't support NO_RBP_MOD feature

Old TDX modules can clobber RBP in the TDH.VP.ENTER SEAMCALL.  However
RBP is used as frame pointer in the x86_64 calling convention, and
clobbering RBP could result in bad things like being unable to unwind
the stack if any non-maskable exceptions (NMI, #MC etc) happens in that
gap.

A new "NO_RBP_MOD" feature was introduced to more recent TDX modules to
not clobber RBP.  This feature is reported in the TDX_FEATURES0 global
metadata field via bit 18.

Don't initialize the TDX module if this feature is not supported [1].

Link: https://lore.kernel.org/all/c0067319-2653-4cbd-8fee-1ccf21b1e646@suse.com/T/#mef98469c51e2382ead2c537ea189752360bd2bef [1]
Signed-off-by: Kai Huang <kai.huang@...el.com>
Reviewed-by: Nikolay Borisov <nik.borisov@...e.com>
---

v2 -> v3:
 - check_module_compatibility() -> check_features().
 - Improve error message.

 https://lore.kernel.org/kvm/cover.1721186590.git.kai.huang@intel.com/T/#md9e2eeef927838cbf20d7b361cdbea518b8aec50

---
 arch/x86/virt/vmx/tdx/tdx.c | 17 +++++++++++++++++
 arch/x86/virt/vmx/tdx/tdx.h |  3 +++
 2 files changed, 20 insertions(+)

diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index fa335ab1ae92..032a53ddf5bc 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -454,6 +454,18 @@ static int get_tdx_sys_info(struct tdx_sys_info *sysinfo)
 	return get_tdx_sys_info_tdmr(&sysinfo->tdmr);
 }
 
+static int check_features(struct tdx_sys_info *sysinfo)
+{
+	u64 tdx_features0 = sysinfo->features.tdx_features0;
+
+	if (!(tdx_features0 & TDX_FEATURES0_NO_RBP_MOD)) {
+		pr_err("frame pointer (RBP) clobber bug present, upgrade TDX module\n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 /* Calculate the actual TDMR size */
 static int tdmr_size_single(u16 max_reserved_per_tdmr)
 {
@@ -1235,6 +1247,11 @@ static int init_tdx_module(void)
 
 	print_basic_sys_info(&sysinfo);
 
+	/* Check whether the kernel can support this module */
+	ret = check_features(&sysinfo);
+	if (ret)
+		return ret;
+
 	/*
 	 * To keep things simple, assume that all TDX-protected memory
 	 * will come from the page allocator.  Make sure all pages in the
diff --git a/arch/x86/virt/vmx/tdx/tdx.h b/arch/x86/virt/vmx/tdx/tdx.h
index e7bed9e717c7..831361e6d0fb 100644
--- a/arch/x86/virt/vmx/tdx/tdx.h
+++ b/arch/x86/virt/vmx/tdx/tdx.h
@@ -154,6 +154,9 @@ struct tdx_sys_info_features {
 	u64 tdx_features0;
 };
 
+/* Architectural bit definitions of TDX_FEATURES0 metadata field */
+#define TDX_FEATURES0_NO_RBP_MOD	_BITULL(18)
+
 /* Class "TDX Module Version" */
 struct tdx_sys_info_version {
 	u16 major;
-- 
2.46.0