x86/virt/tdx: Require the module to assert it has the NO_RBP_MOD mitigation

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.  KVM will need to use the TDH.VP.ENTER SEAMCALL to run
TDX guests.  It won't be safe to run TDX guests w/o this feature.  To
prevent it, just 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".

Signed-off-by: Kai Huang <kai.huang@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.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>
Link: https://lore.kernel.org/fc0e8ab7-86d4-4428-be31-82e1ece6dd21@intel.com/
Link: https://lore.kernel.org/all/76ae5025502c84d799e3a56a6fc4f69a82da8f93.1734188033.git.kai.huang%40intel.com

diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index 43ec56db50840ed108cfaa37d265f71efb40a952..7fdb37387886baebc59afb50dccd73f474ff0989 100644 (file)
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -272,6 +272,18 @@ static int read_sys_metadata_field(u64 field_id, u64 *data)
 
 #include "tdx_global_metadata.c"
 
+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)
 {
@@ -1055,6 +1067,11 @@ 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 641beec86e737992b13d2ce54bbbb58c71a8a7ae..4e3d533cdd61b2bbb8a6681f3a60b0347004cc2d 100644 (file)
--- a/arch/x86/virt/vmx/tdx/tdx.h
+++ b/arch/x86/virt/vmx/tdx/tdx.h
@@ -2,6 +2,7 @@
 #ifndef _X86_VIRT_TDX_H
 #define _X86_VIRT_TDX_H
 
+#include <linux/bits.h>
 #include "tdx_global_metadata.h"
 
 /*
@@ -51,6 +52,9 @@ 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!