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

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Date:   Wed, 23 Feb 2022 16:46:39 +0100
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Reinette Chatre <reinette.chatre@...el.com>
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

On Tue, Feb 22, 2022 at 11:19:11AM -0800, Reinette Chatre wrote:
> 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.

Thank you, also Mark confirmed this.

BR, Jarkko