[PATCH v8 9/9] x86/virt/tdx: Require the module to assert it has the NO_RBP_MOD mitigation

[Kai Huang <kai.huang@intel.com>]

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].

Note the bit definitions of TDX_FEATURES0 are not auto-generated in
tdx_global_metadata.h.  Manually define a macro for it in "tdx.h".

Link: https://lore.kernel.org/fc0e8ab7-86d4-4428-be31-82e1ece6dd21@intel.com/ [1]
Signed-off-by: Kai Huang <kai.huang@intel.com>
Reviewed-by: Nikolay Borisov <nik.borisov@suse.com>
Reviewed-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
---
 arch/x86/virt/vmx/tdx/tdx.c | 17 +++++++++++++++++
 arch/x86/virt/vmx/tdx/tdx.h |  4 ++++
 2 files changed, 21 insertions(+)

diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index b14089f784bf..e4a7e0e17812 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -312,6 +312,18 @@ static int init_tdx_sys_info(struct tdx_sys_info *sysinfo)
 	return 0;
 }
 
+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)
 {
@@ -1095,6 +1107,11 @@ static int init_tdx_module(void)
 	if (ret)
 		return ret;
 
+	/* 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 0128b963b723..c8be00f6b15a 100644
--- a/arch/x86/virt/vmx/tdx/tdx.h
+++ b/arch/x86/virt/vmx/tdx/tdx.h
@@ -5,6 +5,7 @@
 #include <linux/types.h>
 #include <linux/compiler_attributes.h>
 #include <linux/stddef.h>
+#include <linux/bits.h>
 #include "tdx_global_metadata.h"
 
 /*
@@ -54,6 +55,9 @@ struct tdmr_info {
 	DECLARE_FLEX_ARRAY(struct tdmr_reserved_area, reserved_areas);
 } __packed __aligned(TDMR_INFO_ALIGNMENT);
 
+/* Bit definitions of TDX_FEATURES0 metadata field */
+#define TDX_FEATURES0_NO_RBP_MOD	BIT(18)
+
 /*
  * Do not put any hardware-defined TDX structure representations below
  * this comment!
-- 
2.46.2