[PATCH] x86/virt/tdx: Add ENDBR for low level SEAMCALL assembly functions

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

Build warnings about missing ENDBR around making SEAMCALLs[*] were
observed when using some randconfig[1] to build today's Linus's tree.

In the C code, the low level SEAMCALL assembly functions (__seamcall(),
__seamcall_ret() and __seamcall_saved_ret()) are indirectly called via
the common sc_retry() function:

    static inline u64 sc_retry(sc_func_t func, u64 fn,
		    	       struct tdx_module_args *args)
    { ... }

    #define seamcall(_fn, _args) sc_retry(__seamcall, (_fn), (_args))

It turns out compilers may not always be smart enough to figure out how
to call those assembly functions directly.

The disassembly of the vmlinux built from the aforementioned config
confirms that __seamcall*() are indirectly called:

    <sc_retry>:
			       ......

       4c 89 ee                mov    %r13,%rsi
       4c 89 e7                mov    %r12,%rdi
       e8 35 8c 7d 01          call   ffffffff82b3e220 <__pi___x86_indirect_thunk_rbp>
       4c 39 f0                cmp    %r14,%rax

In this case ENDBR is needed at the beginning of __seamcall*().

Change SYM_FUNC_START() to SYM_TYPED_FUNC_START() for __seamcall*() to
add ENDBR to them.

When the compiler can generate direct call for __seamcall*(), the
additional ENDBR is safe since it has no impact to directly called
functions.

When kernel IBT was added to the kernel, initially the SYM_FUNC_START()
had the ENDBR added in commit

  c4691712b546 ("x86/linkage: Add ENDBR to SYM_FUNC_START*()")

However when the commit

  582077c94052 ("x86/cfi: Clean up linkage")

removed the ENDBR from the SYM_FUNC_START() and added it to the
SYM_TYPED_FUNC_START(), it didn't touch the SEAMCALL assembly.

[*] Aforementioned build warning:

vmlinux.o: warning: objtool: try_init_module_global+0x5d: relocation to !ENDBR: __seamcall+0x0
vmlinux.o: warning: objtool: read_sys_metadata_field+0x4a: relocation to !ENDBR: __seamcall_ret+0x0
vmlinux.o: warning: objtool: do_global_key_config+0x36: relocation to !ENDBR: __seamcall+0x0
vmlinux.o: warning: objtool: tdh_phymem_page_reclaim+0x71: relocation to !ENDBR: __seamcall_ret+0x0
vmlinux.o: warning: objtool: tdh_phymem_cache_wb+0x41: relocation to !ENDBR: __seamcall+0x0
vmlinux.o: warning: objtool: tdh_phymem_page_wbinvd_tdr+0x95: relocation to !ENDBR: __seamcall+0x0
vmlinux.o: warning: objtool: tdx_cpu_enable+0x7b: relocation to !ENDBR: __seamcall+0x0
vmlinux.o: warning: objtool: init_tdmr+0x59: relocation to !ENDBR: __seamcall_ret+0x0
vmlinux.o: warning: objtool: config_tdx_module.constprop.0+0x19d: relocation to !ENDBR: __seamcall+0x0
vmlinux.o: warning: objtool: tdh_vp_addcx+0x91: relocation to !ENDBR: __seamcall+0x0
vmlinux.o: warning: objtool: tdh_vp_init+0x76: relocation to !ENDBR: __seamcall+0x0
vmlinux.o: warning: objtool: tdh_vp_wr+0x87: relocation to !ENDBR: __seamcall+0x0
vmlinux.o: warning: objtool: tdh_vp_rd+0x6d: relocation to !ENDBR: __seamcall_ret+0x0
vmlinux.o: warning: objtool: tdh_vp_flush+0x4c: relocation to !ENDBR: __seamcall+0x0
vmlinux.o: warning: objtool: tdh_vp_create+0x85: relocation to !ENDBR: __seamcall+0x0
vmlinux.o: warning: objtool: tdh_mng_create+0x73: relocation to !ENDBR: __seamcall+0x0
vmlinux.o: warning: objtool: tdh_mem_page_aug+0xb4: relocation to !ENDBR: __seamcall_ret+0x0
vmlinux.o: warning: objtool: tdh_mem_sept_add+0xb4: relocation to !ENDBR: __seamcall_ret+0x0
vmlinux.o: warning: objtool: tdh_mem_page_add+0xce: relocation to !ENDBR: __seamcall_ret+0x0
vmlinux.o: warning: objtool: tdh_mng_addcx+0x91: relocation to !ENDBR: __seamcall+0x0
vmlinux.o: warning: objtool: tdh_mem_page_remove+0x7e: relocation to !ENDBR: __seamcall_ret+0x0
vmlinux.o: warning: objtool: tdh_mem_track+0x4c: relocation to !ENDBR: __seamcall+0x0
vmlinux.o: warning: objtool: tdh_mng_init+0x6d: relocation to !ENDBR: __seamcall_ret+0x0
vmlinux.o: warning: objtool: tdh_mng_key_freeid+0x4c: relocation to !ENDBR: __seamcall+0x0
vmlinux.o: warning: objtool: tdh_mng_vpflushdone+0x4c: relocation to !ENDBR: __seamcall+0x0
vmlinux.o: warning: objtool: tdh_mr_finalize+0x4c: relocation to !ENDBR: __seamcall+0x0
vmlinux.o: warning: objtool: tdh_mr_extend+0x77: relocation to !ENDBR: __seamcall_ret+0x0
vmlinux.o: warning: objtool: tdh_mng_rd+0x6d: relocation to !ENDBR: __seamcall_ret+0x0
vmlinux.o: warning: objtool: tdh_mng_key_config+0x4c: relocation to !ENDBR: __seamcall+0x0
vmlinux.o: warning: objtool: tdh_mem_range_block+0x7e: relocation to !ENDBR: __seamcall_ret+0x0
vmlinux.o: warning: objtool: tdh_phymem_page_wbinvd_hkid+0x7d: relocation to !ENDBR: __seamcall+0x0

Fixes: 582077c94052 ("x86/cfi: Clean up linkage")
Link: https://download.01.org/0day-ci/archive/20250524/202505240530.5KktQ5mX-lkp@intel.com/config [1]
Signed-off-by: Kai Huang <kai.huang@intel.com>
---
 arch/x86/virt/vmx/tdx/seamcall.S | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/x86/virt/vmx/tdx/seamcall.S b/arch/x86/virt/vmx/tdx/seamcall.S
index 6854c52c374b..637226ae935d 100644
--- a/arch/x86/virt/vmx/tdx/seamcall.S
+++ b/arch/x86/virt/vmx/tdx/seamcall.S
@@ -1,5 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 #include <linux/linkage.h>
+#include <linux/cfi_types.h>
 #include <asm/frame.h>
 
 #include "tdxcall.S"
@@ -18,7 +19,7 @@
  * Return (via RAX) TDX_SEAMCALL_VMFAILINVALID if the SEAMCALL itself
  * fails, or the completion status of the SEAMCALL leaf function.
  */
-SYM_FUNC_START(__seamcall)
+SYM_TYPED_FUNC_START(__seamcall)
 	TDX_MODULE_CALL host=1
 SYM_FUNC_END(__seamcall)
 
@@ -37,7 +38,7 @@ SYM_FUNC_END(__seamcall)
  * Return (via RAX) TDX_SEAMCALL_VMFAILINVALID if the SEAMCALL itself
  * fails, or the completion status of the SEAMCALL leaf function.
  */
-SYM_FUNC_START(__seamcall_ret)
+SYM_TYPED_FUNC_START(__seamcall_ret)
 	TDX_MODULE_CALL host=1 ret=1
 SYM_FUNC_END(__seamcall_ret)
 
@@ -59,6 +60,6 @@ SYM_FUNC_END(__seamcall_ret)
  * Return (via RAX) TDX_SEAMCALL_VMFAILINVALID if the SEAMCALL itself
  * fails, or the completion status of the SEAMCALL leaf function.
  */
-SYM_FUNC_START(__seamcall_saved_ret)
+SYM_TYPED_FUNC_START(__seamcall_saved_ret)
 	TDX_MODULE_CALL host=1 ret=1 saved=1
 SYM_FUNC_END(__seamcall_saved_ret)

base-commit: 5abc7438f1e9d62e91ad775cc83c9594c48d2282
-- 
2.49.0