linux-kernel - [PATCH v2 0/2] x86/sev-es: Resolve early #VC handler UB

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Message-ID: <20230912002703.3924521-1-acdunlap@google.com>
Date:   Mon, 11 Sep 2023 17:27:01 -0700
From:   Adam Dunlap <acdunlap@...gle.com>
To:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Kim Phillips <kim.phillips@....com>,
        Juergen Gross <jgross@...e.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Adam Dunlap <acdunlap@...gle.com>,
        Joerg Roedel <jroedel@...e.de>
Cc:     Tom Lendacky <thomas.lendacky@....com>,
        David Hildenbrand <david@...hat.com>,
        Mike Rapoport <rppt@...nel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Nikunj A Dadhania <nikunj@....com>,
        Dionna Glaze <dionnaglaze@...gle.com>,
        Peter Gonda <pgonda@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Khalid ElMously <khalid.elmously@...onical.com>,
        Jacob Xu <jacobhxu@...gle.com>
Subject: [PATCH v2 0/2] x86/sev-es: Resolve early #VC handler UB

In v0 of this patch, I mistakenly claimed that
boot_cpu_data.x86_virt_bits was not getting set to 0 in some
configurations. However, it is in fact reliably being set to 0 because
it is specified to be in the .data..read_mostly section, and .data is
initialized at this point. The boot failures that we were seeing were
actually due to the gcc 12.3 compiler exploiting the undefined
behavior to return false from __is_canonical_address when
boot_cpu_data.x86_virt_bits is 0.

This patch set applies the 2 changes posted by Dave Hansen: remove the
UB by explicily checking for 0, and remove the period of time where
x86_virt_bits may be temporarily set to the wrong value where the #VC
handler could observe it.

Adam Dunlap (2):
  x86/sev-es: Allow copy_from_kernel_nofault in earlier boot
  x86/sev-es: Only set x86_virt_bits to correct value

 arch/x86/kernel/cpu/common.c | 37 +++++++++++++++++++++---------------
 arch/x86/mm/maccess.c        | 19 +++++++++++++-----
 2 files changed, 36 insertions(+), 20 deletions(-)

-- 
2.42.0.283.g2d96d420d3-goog