linux-kernel - Re: [PATCH v7 05/22] x86/sev: Move GHCB page based HV communication out of startup code

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]

Message-ID: <20250831111521.GAaLQuyYLUSN24_ZmT@fat_crate.local>
Date: Sun, 31 Aug 2025 13:15:21 +0200
From: Borislav Petkov <bp@...en8.de>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: Ard Biesheuvel <ardb+git@...gle.com>, linux-kernel@...r.kernel.org,
	linux-efi@...r.kernel.org, x86@...nel.org,
	Ingo Molnar <mingo@...nel.org>,
	Kevin Loughlin <kevinloughlin@...gle.com>,
	Tom Lendacky <thomas.lendacky@....com>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Nikunj A Dadhania <nikunj@....com>
Subject: Re: [PATCH v7 05/22] x86/sev: Move GHCB page based HV communication
 out of startup code

On Sun, Aug 31, 2025 at 12:56:41PM +0200, Ard Biesheuvel wrote:
> OK it appears I've fixed it in the wrong place: the next patch adds
> back the definition of has_cpuflag() so I squashed that hunk into the
> wrong patch, it seems.

The real question is - and I'm sceptical - whether the startup code runs too
early for boot_cpu_has(). And how is the startup code going to call
boot_cpu_has().

/me builds .s

Aha, so it gets converted into a boot_cpu_data access:

# arch/x86/boot/startup/sev-shared.c:662:       if (validate && !has_cpuflag(X86_FEATURE_COHERENCY_SFW_NO))
        testb   %r13b, %r13b    # validate
        je      .L46    #,
# ./arch/x86/include/asm/bitops.h:206:          (addr[nr >> _BITOPS_LONG_SHIFT])) != 0;
        movq    80+boot_cpu_data(%rip), %rax    # MEM[(const volatile long unsigned int *)&boot_cpu_data + 80B], _15
# arch/x86/boot/startup/sev-shared.c:662:       if (validate && !has_cpuflag(X86_FEATURE_COHERENCY_SFW_NO))

But former question remains: AFAIK, you want to run the startup code waaay
earlier, before we do identify_boot_cpu() which prepares boot_cpu_data, right?

-- 
Regards/Gruss,
    Boris.

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