Re: [PATCH] x86/tdx: Make seamcall/tdcall CET-compliant

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

On Wed, 2025-10-22 at 12:36 +0300, Nikolay Borisov wrote:
> _seamcall/_ret/_saved_ret can be the target of indirect calls via
> sc_retry_prerr/__seamcall_dirty_cache so on machines with CET enabled
> such call chains result in a  splat and a BUG():
> 

[...]

> 
> Fix it by adding an ENBDR in TDX_MODULE_CALL macro to cover all
> cases.
> 
> Signed-off-by: Nikolay Borisov <nik.borisov@suse.com>
> ---
> 
> The kernel this was observed is a SLE, however it contains the current upstream
> TDX patches. And looking at the usptream code the problem persists there as well.

Does your kernel contain commit 0b3bc018e86af ("x86/virt/tdx: Avoid
indirect calls to TDX assembly functions")?

Some history about this commit:

I firstly found __seamcall*() could be indirect calls in some randconfig
when building the kernel, and tried to resolve it by (effectively) adding
ENDBR:

https://lore.kernel.org/lkml/20250604003848.13154-1-kai.huang@intel.com/

Peter suggested that we could use __always_inline to keep compiler from
generating indirect calls (which resulted in the above commit):

https://lore.kernel.org/lkml/20250605145914.GW39944@noisy.programming.kicks-ass.net/

I never met __tdcall*() could be indirect calls, though.

> 
>  arch/x86/virt/vmx/tdx/tdxcall.S | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/x86/virt/vmx/tdx/tdxcall.S b/arch/x86/virt/vmx/tdx/tdxcall.S
> index 016a2a1ec1d6..a2137cd7a669 100644
> --- a/arch/x86/virt/vmx/tdx/tdxcall.S
> +++ b/arch/x86/virt/vmx/tdx/tdxcall.S
> @@ -43,6 +43,7 @@
>   * TDH.EXPORT.MEM.
>   */
>  .macro TDX_MODULE_CALL host:req ret=0 saved=0
> +	ENDBR
>  	FRAME_BEGIN
> 
>  	/* Move Leaf ID to RAX */
> --
> 2.51.1