[PATCH 9/9] x86/virt/tdx: Don't initialize module that doesn't support NO_RBP_MOD feature

Kai Huang
2024-06-16T12:02:16Z

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@intel.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