linux-kernel - Re: [PATCH v15 05/23] x86/virt/tdx: Handle SEAMCALL no entropy error in common 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: <20231115192650.GB1109547@ls.amr.corp.intel.com>
Date:   Wed, 15 Nov 2023 11:26:50 -0800
From:   Isaku Yamahata <isaku.yamahata@...ux.intel.com>
To:     "Huang, Kai" <kai.huang@...el.com>
Cc:     "isaku.yamahata@...ux.intel.com" <isaku.yamahata@...ux.intel.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "david@...hat.com" <david@...hat.com>,
        "bagasdotme@...il.com" <bagasdotme@...il.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "seanjc@...gle.com" <seanjc@...gle.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "nik.borisov@...e.com" <nik.borisov@...e.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "imammedo@...hat.com" <imammedo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "Gao, Chao" <chao.gao@...el.com>,
        "rafael@...nel.org" <rafael@...nel.org>,
        "Brown, Len" <len.brown@...el.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH v15 05/23] x86/virt/tdx: Handle SEAMCALL no entropy error
 in common code

On Wed, Nov 15, 2023 at 10:41:46AM +0000,
"Huang, Kai" <kai.huang@...el.com> wrote:

> 
> > > +#include <asm/archrandom.h>
> > > +
> > > +typedef u64 (*sc_func_t)(u64 fn, struct tdx_module_args *args);
> > > +
> > > +static inline u64 sc_retry(sc_func_t func, u64 fn,
> > > +			   struct tdx_module_args *args)
> > > +{
> > > +	int retry = RDRAND_RETRY_LOOPS;
> > > +	u64 ret;
> > > +
> > > +	do {
> > > +		ret = func(fn, args);
> > > +	} while (ret == TDX_RND_NO_ENTROPY && --retry);
> > 
> > This loop assumes that args isn't touched when TDX_RND_NO_ENTRYPOY is returned.
> > It's not true.  TDH.SYS.INIT() and TDH.SYS.LP.INIT() clear RCX, RDX, etc on
> > error including TDX_RND_NO_ENTRY.  Because TDH.SYS.INIT() takes RCX as input,
> > this wrapper doesn't work.  TDH.SYS.LP.INIT() doesn't use RCX, RDX ... as
> > input. So it doesn't matter.
> > 
> > Other SEAMCALLs doesn't touch registers on the no entropy error.
> > TDH.EXPORTS.STATE.IMMUTABLE(), TDH.IMPORTS.STATE.IMMUTABLE(), TDH.MNG.ADDCX(),
> > and TDX.MNG.CREATE().  TDH.SYS.INIT() is an exception.
> 
> If I am reading the spec (TDX module 1.5 ABI) correctly the TDH.SYS.INIT doesn't
> return TDX_RND_NO_ENTROPY.

The next updated spec would fix it.
                                  

> TDH.SYS.LP.INIT indeed can return NO_ENTROPY but as
> you said it doesn't take any register as input.  So technically the code works
> fine.  (Even the TDH.SYS.INIT can return NO_ENTROPY the code still works fine
> because the RCX must be 0 for TDH.SYS.INIT.)

Ah yes, I agree with you. So it doesn't matter.


> Also, I can hardly think out of any reason why TDX module needs to clobber input
> registers in case of NO_ENTROPY for *ANY* SEAMCALL.  But despite that, I am not
> opposing the idea that it *MIGHT* be better to "not assume" NO_ENTROPY will
> never clobber registers either, e.g., for the sake of future extendibility.  In
> this case, the below diff should address:

Now we agreed that TDH.SYS.INIT() and TDH.SYS.LP.INIT() doesn't matter,
I'm fine with this patch. (TDX KVM handles other SEAMCALLS itself.)

Reviewed-by: Isaku Yamahata <isaku.yamahata@...el.com>
-- 
Isaku Yamahata <isaku.yamahata@...ux.intel.com>