linux-kernel - Re: [PATCH v9 05/18] x86/virt/tdx: Add SEAMCALL infrastructure

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 13 Feb 2023 09:48:33 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Kai Huang <kai.huang@...el.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     linux-mm@...ck.org, peterz@...radead.org, tglx@...utronix.de,
        seanjc@...gle.com, pbonzini@...hat.com, dan.j.williams@...el.com,
        rafael.j.wysocki@...el.com, kirill.shutemov@...ux.intel.com,
        ying.huang@...el.com, reinette.chatre@...el.com,
        len.brown@...el.com, tony.luck@...el.com, ak@...ux.intel.com,
        isaku.yamahata@...el.com, chao.gao@...el.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, david@...hat.com,
        bagasdotme@...il.com, sagis@...gle.com, imammedo@...hat.com
Subject: Re: [PATCH v9 05/18] x86/virt/tdx: Add SEAMCALL infrastructure

On 2/13/23 03:59, Kai Huang wrote:
> diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
> index 4a3ee64c1ca7..5c5ecfddb15b 100644
> --- a/arch/x86/include/asm/tdx.h
> +++ b/arch/x86/include/asm/tdx.h
> @@ -8,6 +8,10 @@
>  #include <asm/ptrace.h>
>  #include <asm/shared/tdx.h>
>  
> +#ifdef CONFIG_INTEL_TDX_HOST
...
> +#define TDX_SEAMCALL_GP			(TDX_SW_ERROR | X86_TRAP_GP)
> +#define TDX_SEAMCALL_UD			(TDX_SW_ERROR | X86_TRAP_UD)
> +
> +#endif

All these kinds of header #ifdefs do it make it harder to write code in
.c files without matching #ifdefs.  Think of code like this completely
made up example:

	if (!tdx_enable()) {
		// Success!  Make a seamcall:
		int something = tdx_seamcall();
		if (something == TDX_SEAMCALL_UD)
			// oh no!
	}

tdx_enable() can never return 0 if CONFIG_INTEL_TDX_HOST=n, so the
entire if() block is optimized away by the compiler.  *BUT*, if you've
#ifdef'd away TDX_SEAMCALL_UD, you'll get a compile error.  People
usually fix the compile error like this:

	if (!tdx_enable()) {
#ifdef CONFIG_INTEL_TDX_HOST
		// Success!  Make a seamcall:
		int something = tdx_seamcall();
		if (something == TDX_SEAMCALL_UD)
			// oh no!
#endif
	}

Which isn't great.

Defining things unconditionally in header files is *FINE*, as long as
the #ifdefs are there somewhere to make the code go away at compile time.

Please post an updated (and tested) patch as a reply to this.