linux-kernel - Re: [PATCH v10 7/9] KVM: VMX: Implement and wire get_untagged

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: <ZN1HT61WM0Pmxqmr@google.com>
Date:   Wed, 16 Aug 2023 15:01:51 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Binbin Wu <binbin.wu@...ux.intel.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        pbonzini@...hat.com, chao.gao@...el.com, kai.huang@...el.com,
        David.Laight@...lab.com, robert.hu@...ux.intel.com,
        guang.zeng@...el.com
Subject: Re: [PATCH v10 7/9] KVM: VMX: Implement and wire get_untagged_addr()
 for LAM

On Wed, Jul 19, 2023, Binbin Wu wrote:
> +	return (sign_extend64(gva, lam_bit) & ~BIT_ULL(63)) | (gva & BIT_ULL(63));

Almost forgot.  Please add a comment explaning how LAM untags the address,
specifically the whole bit 63 preservation.  The logic is actually straightforward,
but the above looks way more complex than it actually is.  This?

	/*
	 * Untag the address by sign-extending the LAM bit, but NOT to bit 63.
	 * Bit 63 is retained from the raw virtual address so that untagging
	 * doesn't change a user access to a supervisor access, and vice versa.
	 */