linux-kernel - Re: [PATCH] x86/sgx: Allow RW for TCS pages

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Message-ID: <YkRyPzaYlbDZg7bR@iki.fi>
Date:   Wed, 30 Mar 2022 18:07:43 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Reinette Chatre <reinette.chatre@...el.com>
Cc:     linux-sgx@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/sgx: Allow RW for TCS pages

On Mon, Mar 28, 2022 at 01:28:39PM -0700, Reinette Chatre wrote:
> Hi Jarkko,
> 
> On 3/19/2022 9:30 AM, Jarkko Sakkinen wrote:
> > Not allowing to set RW for added TCS pages leads only to a special case
> > to be handled in the user space run-time. Thus, allow permissions to be
> > set RW. Originally, it would have probably made more sense to check up
> > that the permissions are RW.
> > 
> > Signed-off-by: Jarkko Sakkinen <jarkko@...nel.org>
> > ---
> >  arch/x86/kernel/cpu/sgx/ioctl.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
> > index 83df20e3e633..f79761ad0400 100644
> > --- a/arch/x86/kernel/cpu/sgx/ioctl.c
> > +++ b/arch/x86/kernel/cpu/sgx/ioctl.c
> > @@ -215,7 +215,7 @@ static int sgx_validate_secinfo(struct sgx_secinfo *secinfo)
> >  	 * CPU will silently overwrite the permissions as zero, which means
> >  	 * that we need to validate it ourselves.
> >  	 */
> > -	if (pt == SGX_SECINFO_TCS && perm)
> > +	if (pt == SGX_SECINFO_TCS && (perm != 0 || perm != (PROT_READ | PROT_WRITE)))
> >  		return -EINVAL;
> >  
> >  	if (secinfo->flags & SGX_SECINFO_RESERVED_MASK)
> 
> The comments above sgx_ioc_enclave_add_pages() seem to indicate that zero 
> permissions are required:
> 
> "A SECINFO for a TCS is required to always contain zero permissions because
>  CPU silently zeros them. Allowing anything else would cause a mismatch in
>  the measurement."

I think this can be left out for now but fixing the relative addressing
is an obvious fix.

BR, Jarkko