[PATCH] x86/tdx: refactor deprecated strncpy

[Justin Stitt]

`strncpy` is deprecated and we should prefer more robust string apis.

In this case, `message.str` is not expected to be NUL-terminated as it
is simply a buffer of characters residing in a union which allows for
named fields representing 8 bytes each. There is only one caller of
`tdx_panic()` and they use a 59-length string for `msg`:
|	const char *msg = "TD misconfiguration: SEPT_VE_DISABLE attribute must be set.";

Given all this information, let's use `strtomem_pad` as this matches the
functionality of `strncpy` in this instances whilst being a more robust
and easier to understand interface.

Link: www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings[1]
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@xxxxxxxxxxxxxxx
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Signed-off-by: Justin Stitt <justinstitt@xxxxxxxxxx>
---
Note: build-tested
---
 arch/x86/coco/tdx/tdx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index 1d6b863c42b0..2e1be592c220 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -119,7 +119,7 @@ static void __noreturn tdx_panic(const char *msg)
 	} message;
 
 	/* VMM assumes '\0' in byte 65, if the message took all 64 bytes */
-	strncpy(message.str, msg, 64);
+	strtomem_pad(message.str, msg, '\0');
 
 	args.r8  = message.r8;
 	args.r9  = message.r9;

---
base-commit: 2dde18cd1d8fac735875f2e4987f11817cc0bc2c
change-id: 20230911-strncpy-arch-x86-coco-tdx-tdx-c-98b0b966bb8d

Best regards,
--
Justin Stitt <justinstitt@xxxxxxxxxx>