linux-kernel - [PATCH 9/9] x86/virt/tdx: Don't initialize module that doesn't support NO_RBP

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Date: Mon, 17 Jun 2024 00:01:19 +1200
From: Kai Huang <kai.huang@...el.com>
To: linux-kernel@...r.kernel.org
Cc: x86@...nel.org,
	dave.hansen@...el.com,
	dan.j.williams@...el.com,
	kirill.shutemov@...ux.intel.com,
	rick.p.edgecombe@...el.com,
	peterz@...radead.org,
	tglx@...utronix.de,
	bp@...en8.de,
	mingo@...hat.com,
	hpa@...or.com,
	seanjc@...gle.com,
	pbonzini@...hat.com,
	kvm@...r.kernel.org,
	isaku.yamahata@...el.com,
	binbin.wu@...ux.intel.com,
	kai.huang@...el.com
Subject: [PATCH 9/9] 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>
---
 arch/x86/virt/vmx/tdx/tdx.c | 17 +++++++++++++++++
 arch/x86/virt/vmx/tdx/tdx.h |  1 +
 2 files changed, 18 insertions(+)

diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index 88a0c8b788b7..c4ff68b565e8 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -487,6 +487,18 @@ static int get_tdx_sysinfo(struct tdx_sysinfo *sysinfo)
 	return get_tdx_tdmr_sysinfo(&sysinfo->tdmr_info);
 }
 
+static int check_module_compatibility(struct tdx_sysinfo *sysinfo)
+{
+	u64 tdx_features0 = sysinfo->module_info.tdx_features0;
+
+	if (!(tdx_features0 & TDX_FEATURES0_NO_RBP_MOD)) {
+		pr_err("NO_RBP_MOD feature is not supported\n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 /* Calculate the actual TDMR size */
 static int tdmr_size_single(u16 max_reserved_per_tdmr)
 {
@@ -1304,6 +1316,11 @@ static int init_tdx_module(void)
 
 	print_basic_sysinfo(&sysinfo);
 
+	/* Check whether the kernel can support this module */
+	ret = check_module_compatibility(&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 be93b6f31e5b..295c3b6d9505 100644
--- a/arch/x86/virt/vmx/tdx/tdx.h
+++ b/arch/x86/virt/vmx/tdx/tdx.h
@@ -148,6 +148,7 @@ struct tdx_sysinfo_module_info {
 };
 
 #define TDX_SYS_ATTR_DEBUG_MODULE	0x1
+#define TDX_FEATURES0_NO_RBP_MOD	_BITULL(18)
 
 /* Class "TDX Module Version" */
 struct tdx_sysinfo_module_version {
-- 
2.43.2