[v2] TDX host: metadata reading tweaks, bug fix and info dump

[PATCH v2 10/10] x86/virt/tdx: Don't initialize module that doesn't support NO_RBP_MOD feature

Posted by Kai Huang 1 year, 5 months ago

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>
Reviewed-by: Nikolay Borisov <nik.borisov@suse.com>
---

v1 -> v2:
 - Add tag from Nikolay.

---
 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 3c19295f1f8f..ec6156728423 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -484,6 +484,18 @@ 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)
 {
@@ -1266,6 +1278,11 @@ 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 4b43eb774ffa..20fd7cb5937a 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 {
-- 
2.45.2

Re: [PATCH v2 10/10] x86/virt/tdx: Don't initialize module that doesn't support NO_RBP_MOD feature

Posted by Dan Williams 1 year, 4 months ago

Kai Huang wrote:
> 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>
> Reviewed-by: Nikolay Borisov <nik.borisov@suse.com>
> ---
> 
> v1 -> v2:
>  - Add tag from Nikolay.
> 
> ---
>  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 3c19295f1f8f..ec6156728423 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -484,6 +484,18 @@ 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)

How about check_features()? Almost everything having to do with TDX
concerns the TDX module, so using "module" in a symbol name rarely adds
any useful context.

> +{
> +	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");

A user would have no idea with this error message how about something
like:

pr_err("frame pointer (RBP) clobber bug present, upgrade TDX module\n");

Re: [PATCH v2 10/10] x86/virt/tdx: Don't initialize module that doesn't support NO_RBP_MOD feature

Posted by Huang, Kai 1 year, 4 months ago

On Mon, 2024-08-05 at 21:55 -0700, Williams, Dan J wrote:
> Kai Huang wrote:
> > 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>
> > Reviewed-by: Nikolay Borisov <nik.borisov@suse.com>
> > ---
> > 
> > v1 -> v2:
> >  - Add tag from Nikolay.
> > 
> > ---
> >  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 3c19295f1f8f..ec6156728423 100644
> > --- a/arch/x86/virt/vmx/tdx/tdx.c
> > +++ b/arch/x86/virt/vmx/tdx/tdx.c
> > @@ -484,6 +484,18 @@ 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)
> 
> How about check_features()? Almost everything having to do with TDX
> concerns the TDX module, so using "module" in a symbol name rarely adds
> any useful context.

Yeah fine to me.  Will do.
> 
> > +{
> > +	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");
> 
> A user would have no idea with this error message how about something
> like:
> 
> pr_err("frame pointer (RBP) clobber bug present, upgrade TDX module\n");

Yeah this is certainly better.  Will do.  Thanks!