linux-kernel - Re: [PATCH V2 19/32] x86/sgx: Support adding of pages to an initialized enclave

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Message-ID: <80f3d7b9-e3d5-b2c0-7707-710bf6f5081e@intel.com>
Date:   Tue, 22 Feb 2022 11:19:11 -0800
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>
CC:     <dave.hansen@...ux.intel.com>, <tglx@...utronix.de>,
        <bp@...en8.de>, <luto@...nel.org>, <mingo@...hat.com>,
        <linux-sgx@...r.kernel.org>, <x86@...nel.org>, <seanjc@...gle.com>,
        <kai.huang@...el.com>, <cathy.zhang@...el.com>,
        <cedric.xing@...el.com>, <haitao.huang@...el.com>,
        <mark.shanahan@...el.com>, <hpa@...or.com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 19/32] x86/sgx: Support adding of pages to an
 initialized enclave

Hi Jarkko,

On 2/20/2022 10:40 AM, Jarkko Sakkinen wrote:
...
 
> Do you know if it is possible to do EAUG, EMODPR and the do a single
> EACCEPT for both? Just looking at pseudo-code, it looked doable but
> I need to check this.
> 
> I.e. EAUG has this
> 
> EPCM(DS:RCX).BLOCKED := 0;
> EPCM(DS:RCX).PENDING := 1;
> EPCM(DS:RCX).MODIFIED := 0;
> EPCM(DS:RCX).PR := 0;
> (* associate the EPCPAGE with the SECS by storing the SECS identifier of DS:TMP_SECS *)
> Update EPCM(DS:RCX) SECS identifier to reference DS:TMP_SECS identifier;
> (* Set EPCM valid fields *)
> EPCM(DS:RCX).VALID := 1;
> 
> And EMODPR only checks .VALID.

After that check there is also:
IF (EPCM(DS:RCX).PENDING is not 0 or (EPCM(DS:RCX).MODIFIED is not 0) )
    THEN
        RFLAGS.ZF := 1;
        RAX := SGX_PAGE_NOT_MODIFIABLE;
        GOTO DONE;
FI;

Attempting the SGX_IOC_ENCLAVE_RESTRICT_PERMISSIONS ioctl() on a recently
added page (EAUG) that has not yet been EACCEPTed is thus expected to fail
with errno of EFAULT (indicating ENCLS[EMODPR] failure) and the returned
structure's result field set to 20 (SGX_PAGE_NOT_MODIFIABLE).

I confirmed this behavior by modifying the "augment" kselftest test by adding
a SGX_IOC_ENCLAVE_RESTRICT_PERMISSIONS call between the new memory access and
the EACCEPT.

Reinette