linux-kernel - Re: [PATCH v3 4/5] x86/tdx: tdx_mcall_get_report0: Return -EBUSY on TDCALL_OPERAND

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: <67f601e35845f_720529475@dwillia2-xfh.jf.intel.com.notmuch>
Date: Tue, 8 Apr 2025 22:13:07 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Cedric Xing <cedric.xing@...el.com>, Dan Williams
	<dan.j.williams@...el.com>, "Kirill A. Shutemov"
	<kirill.shutemov@...ux.intel.com>, Dave Hansen <dave.hansen@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>, <x86@...nel.org>, "H. Peter Anvin"
	<hpa@...or.com>
CC: <linux-kernel@...r.kernel.org>, <linux-coco@...ts.linux.dev>, "Dionna
 Amalie Glaze" <dionnaglaze@...gle.com>, Guorui Yu
	<guorui.yu@...ux.alibaba.com>, James Bottomley
	<James.Bottomley@...senpartnership.com>, Dan Middleton
	<dan.middleton@...ux.intel.com>, Mikko Ylinen <mikko.ylinen@...ux.intel.com>,
	Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@...ux.intel.com>
Subject: Re: [PATCH v3 4/5] x86/tdx: tdx_mcall_get_report0: Return -EBUSY on
 TDCALL_OPERAND_BUSY error

Cedric Xing wrote:
> Return `-EBUSY` from tdx_mcall_get_report0() when `TDG.MR.REPORT` returns
> `TDCALL_OPERAND_BUSY`. This enables the caller to retry obtaining a
> TDREPORT later if another VCPU is extending an RTMR concurrently.

Can this not be prevented by proper locking? Otherwise this type of
collision sounds like a kernel bug, not something that should escape to
userspace.

I.e. userspace can not reasonably know when it is safe to retry, so take
locks to ensure forward progress.