linux-kernel - Re: [PATCH v3 03/19] x86/startup_64: Drop long return to initial

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Message-ID: <20240131162952.GHZbp1gH7C7lNMRUru@fat_crate.local>
Date: Wed, 31 Jan 2024 17:29:52 +0100
From: Borislav Petkov <bp@...en8.de>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: Ard Biesheuvel <ardb+git@...gle.com>, linux-kernel@...r.kernel.org,
	Kevin Loughlin <kevinloughlin@...gle.com>,
	Tom Lendacky <thomas.lendacky@....com>,
	Dionna Glaze <dionnaglaze@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Andy Lutomirski <luto@...nel.org>, Arnd Bergmann <arnd@...db.de>,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Kees Cook <keescook@...omium.org>, Brian Gerst <brgerst@...il.com>,
	linux-arch@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH v3 03/19] x86/startup_64: Drop long return to
 initial_code pointer

On Wed, Jan 31, 2024 at 03:07:50PM +0100, Ard Biesheuvel wrote:
> > s/int3/RET seems to do the trick.
> >
> or ud2, even better,

Yap, that does it. And yes, we don't return here. I guess objtool
complains because

"7. file: warning: objtool: func()+0x5c: stack state mismatch

   The instruction's frame pointer state is inconsistent, depending on
   which execution path was taken to reach the instruction.

   ...

   Another possibility is that the code has some asm or inline asm which
   does some unusual things to the stack or the frame pointer.  In such
   cases it's probably appropriate to use the unwind hint macros in
   asm/unwind_hints.h.
"

Lemme test this one a bit on my machines and queue it.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette