linux-kernel - Re: [PATCH] x86/sgx: fix a NULL pointer

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Message-ID: <dfb1f233-aebd-50cf-8704-e83b91ee110a@intel.com>
Date:   Tue, 18 Jul 2023 07:27:49 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Haitao Huang <haitao.huang@...ux.intel.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        dave.hansen@...ux.intel.com, linux-kernel@...r.kernel.org,
        linux-sgx@...r.kernel.org, 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:     kai.huang@...el.com, reinette.chatre@...el.com,
        kristen@...ux.intel.com, seanjc@...gle.com, stable@...r.kernel.org
Subject: Re: [PATCH] x86/sgx: fix a NULL pointer

On 7/17/23 13:29, Haitao Huang wrote:
> Under heavy load, the SGX EPC reclaimers (current ksgxd or future EPC
> cgroup worker) may reclaim the SECS EPC page for an enclave and set
> encl->secs.epc_page to NULL. But the SECS EPC page is used for EAUG in
> the SGX #PF handler without checking for NULL and reloading.
> 
> Fix this by checking if SECS is loaded before EAUG and load it if it was
> reclaimed.

It would be nice to see a _bit_ more theory of the bug in here.

What is an SECS page and why is it special in a reclaim context?  Why is
this so hard to hit?  What led you to discover this issue now?  What is
EAUG?