linux-kernel - Re: [PATCH] x86/sgx: Synchronize encl->srcu in sgx_encl

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Date:   Tue, 15 Dec 2020 07:55:56 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        linux-sgx@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH] x86/sgx: Synchronize encl->srcu in sgx_encl_release().

On Mon, Dec 14, 2020 at 11:01:32AM -0800, Sean Christopherson wrote:
> On Fri, Dec 11, 2020, Jarkko Sakkinen wrote:
> > Each sgx_mmun_notifier_release() starts a grace period, which means that
> 
> Should be sgx_mmu_notifier_release(), here and in the comment.

Thanks.

> > one extra synchronize_rcu() in sgx_encl_release(). Add it there.
> > 
> > sgx_release() has the loop that drains the list but with bad luck the
> > entry is already gone from the list before that loop processes it.
> 
> Why not include the actual analysis that "proves" the bug?  The splat that
> Haitao reported would also be useful info.

True. I can include a snippet of dmesg to the commit message.

> > Fixes: 1728ab54b4be ("x86/sgx: Add a page reclaimer")
> > Cc: Borislav Petkov <bp@...en8.de>
> > Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> > Reported-by: Sean Christopherson <seanjc@...gle.com>
> 
> Haitao reported the bug, and for all intents and purposes provided the fix.  I
> just did the analysis to verify that there was a legitimate bug and that the
> synchronization in sgx_encl_release() was indeed necessary.

Good and valid point. The way I see it, the tags should be:

Reported-by: Haitao Huang <haitao.huang@...ux.intel.com>
Suggested-by: Sean Christopherson <seanjc@...gle.com>

Haitao pointed out the bug but from your analysis I could resolve that
this is the fix to implement, and was able to write the long
description for the commit.

Does this make sense to you?

/Jarkko