linux-kernel - Re: [PATCH 01/16] KVM: MMU: pass unadulterated gpa to direct_page

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: <YTAEqXlvNOgY5hII@google.com>
Date:   Wed, 1 Sep 2021 22:54:33 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        isaku.yamahata@...el.com, David Matlack <dmatlack@...gle.com>,
        peterx@...hat.com
Subject: Re: [PATCH 01/16] KVM: MMU: pass unadulterated gpa to
 direct_page_fault

On Sat, Aug 07, 2021, Paolo Bonzini wrote:
> Do not bother removing the low bits of the gpa.  This masking dates back
> to the very first commit of KVM but it is unnecessary---or even
> problematic, because the gpa is later used to fill in the MMIO page cache.

I don't disagree with the code change, but I don't see how stripping the offset
can be problematic for the MMIO page cache.  I assume you're referring to
handle_abnormal_pfn() -> vcpu_cache_mmio_info().  The "gva" is masked with
PAGE_MASK, i.e. the offset is stripped anyways.  And fundamentally, that cache
is tied to the granularity of the memslots, tracking the offset would be wrong.