linux-kernel - [PATCH] x86/tdx: refactor deprecated strncpy

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Message-ID: <20230911-strncpy-arch-x86-coco-tdx-tdx-c-v1-1-4b38155727f3@google.com>
Date:   Mon, 11 Sep 2023 18:27:25 +0000
From:   Justin Stitt <justinstitt@...gle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>
Cc:     linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
        Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH] x86/tdx: refactor deprecated strncpy

`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@...r.kernel.org
Cc: Kees Cook <keescook@...omium.org>
Cc: Nick Desaulniers <ndesaulniers@...gle.com>
Signed-off-by: Justin Stitt <justinstitt@...gle.com>
---
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@...gle.com>