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From: Dave Hansen <dave.hansen@intel.com>
To: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
	"Xing, Cedric" <cedric.xing@intel.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
	Jethro Beekman <jethro@fortanix.com>,
	Sean Christopherson <sean.j.christopherson@intel.com>,
	linux-sgx@vger.kernel.org, x86@kernel.org,
	Haitao Huang <haitao.huang@linux.intel.com>,
	Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Andy Lutomirski <luto@amacapital.net>
Subject: Re: [PATCH] x86/vdso: Remove retpoline from SGX vDSO call
Date: Wed, 30 Sep 2020 14:46:05 -0700	[thread overview]
Message-ID: <bc09f081-d0e8-20dc-350e-c7dbdf077a52@intel.com> (raw)
In-Reply-To: <20200930213625.GA66129@linux.intel.com>

On 9/30/20 2:36 PM, Jarkko Sakkinen wrote:
> 1. Full reptoline is the safest alternative and we have it done already.

I wouldn't feel _quite_ comfortable saying this.

LFENCEs have architecturally defined behavior.  Retpolines have zero
future guarantees in the architecture.  I'll take an LFENCE that (versus
a retpoline) is:

1. Less code
2. Never has to be patched
3. Never causes functional problems (like with CET)
4. Has architectural semantics

The only advantage retpolines offer is that they have a well-defined
mitigations on existing microarchitectures.

To me, an LFENCE is waaaaaaay "safer".

  reply	other threads:[~2020-09-30 21:46 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-30 14:01 [PATCH] x86/vdso: Remove retpoline from SGX vDSO call Jarkko Sakkinen
2020-09-30 14:08 ` Dave Hansen
2020-09-30 14:20   ` Jarkko Sakkinen
2020-09-30 14:33     ` Dave Hansen
2020-09-30 15:28       ` Jarkko Sakkinen
2020-09-30 15:43         ` Sean Christopherson
2020-09-30 16:28           ` Dave Hansen
2020-09-30 17:01             ` Jethro Beekman
2020-09-30 18:09               ` Andrew Cooper
2020-09-30 19:25                 ` Jarkko Sakkinen
2020-09-30 20:45                   ` Xing, Cedric
2020-09-30 21:22                     ` Jarkko Sakkinen
2020-09-30 21:36                       ` Jarkko Sakkinen
2020-09-30 21:46                         ` Dave Hansen [this message]
2020-09-30 23:41                           ` Jarkko Sakkinen
2020-09-30 16:38           ` Jarkko Sakkinen

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