Commit 0b3bc018 authored by Kai Huang's avatar Kai Huang Committed by Dave Hansen
Browse files

x86/virt/tdx: Avoid indirect calls to TDX assembly functions 



Two 'static inline' TDX helper functions (sc_retry() and
sc_retry_prerr()) take function pointer arguments which refer to
assembly functions.  Normally, the compiler inlines the TDX helper,
realizes that the function pointer targets are completely static --
thus can be resolved at compile time -- and generates direct call
instructions.

But, other times (like when CONFIG_CC_OPTIMIZE_FOR_SIZE=y), the
compiler declines to inline the helpers and will instead generate
indirect call instructions.

Indirect calls to assembly functions require special annotation (for
various Control Flow Integrity mechanisms).  But TDX assembly
functions lack the special annotations and can only be called
directly.

Annotate both the helpers as '__always_inline' to prod the compiler
into maintaining the direct calls. There is no guarantee here, but
Peter has volunteered to report the compiler bug if this assumption
ever breaks[1].

Fixes: 1e66a7e2 ("x86/virt/tdx: Handle SEAMCALL no entropy error in common code")
Fixes: df01f5ae ("x86/virt/tdx: Add SEAMCALL error printing for module initialization")
Signed-off-by: default avatarKai Huang <kai.huang@intel.com>
Signed-off-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/lkml/20250605145914.GW39944@noisy.programming.kicks-ass.net/ [1]
Link: https://lore.kernel.org/all/20250606130737.30713-1-kai.huang%40intel.com
parent f2878226

arch/x86/include/asm/tdx.h

+1 −1
Original line number Diff line number Diff line
@@ -106,7 +106,7 @@ void tdx_init(void); 


typedef u64 (*sc_func_t)(u64 fn, struct tdx_module_args *args);



static inline u64 sc_retry(sc_func_t func, u64 fn,

static __always_inline u64 sc_retry(sc_func_t func, u64 fn,

			   struct tdx_module_args *args)

{

	int retry = RDRAND_RETRY_LOOPS;

arch/x86/virt/vmx/tdx/tdx.c

+3 −2
Original line number Diff line number Diff line
@@ -75,7 +75,8 @@ static inline void seamcall_err_ret(u64 fn, u64 err, 
			args->r9, args->r10, args->r11);

}



static inline int sc_retry_prerr(sc_func_t func, sc_err_func_t err_func,

static __always_inline int sc_retry_prerr(sc_func_t func,

					  sc_err_func_t err_func,

					  u64 fn, struct tdx_module_args *args)

{

	u64 sret = sc_retry(func, fn, args);