Re: [PATCH v3 8/8] x86/virt/tdx: Don't initialize module that doesn't support NO_RBP_MOD feature

From: Adrian Hunter
Date: Fri Aug 30 2024 - 07:03:13 EST


On 27/08/24 10:14, 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@xxxxxxxx/T/#mef98469c51e2382ead2c537ea189752360bd2bef [1]
> Signed-off-by: Kai Huang <kai.huang@xxxxxxxxx>
> Reviewed-by: Nikolay Borisov <nik.borisov@xxxxxxxx>

Reviewed-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>

> ---
>
> v2 -> v3:
> - check_module_compatibility() -> check_features().
> - Improve error message.
>
> https://lore.kernel.org/kvm/cover.1721186590.git.kai.huang@xxxxxxxxx/T/#md9e2eeef927838cbf20d7b361cdbea518b8aec50
>
> ---
> arch/x86/virt/vmx/tdx/tdx.c | 17 +++++++++++++++++
> arch/x86/virt/vmx/tdx/tdx.h | 3 +++
> 2 files changed, 20 insertions(+)
>
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index fa335ab1ae92..032a53ddf5bc 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -454,6 +454,18 @@ static int get_tdx_sys_info(struct tdx_sys_info *sysinfo)
> return get_tdx_sys_info_tdmr(&sysinfo->tdmr);
> }
>
> +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)
> {
> @@ -1235,6 +1247,11 @@ static int init_tdx_module(void)
>
> print_basic_sys_info(&sysinfo);
>
> + /* 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 e7bed9e717c7..831361e6d0fb 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.h
> +++ b/arch/x86/virt/vmx/tdx/tdx.h
> @@ -154,6 +154,9 @@ struct tdx_sys_info_features {
> u64 tdx_features0;
> };
>
> +/* Architectural bit definitions of TDX_FEATURES0 metadata field */
> +#define TDX_FEATURES0_NO_RBP_MOD _BITULL(18)
> +
> /* Class "TDX Module Version" */
> struct tdx_sys_info_version {
> u16 major;