linux-kernel - Re: [PATCH v33 03/21] x86/mm: x86/sgx: Signal SIGSEGV with PF

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Date:   Thu, 25 Jun 2020 23:52:11 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     x86@...nel.org, linux-sgx@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Jethro Beekman <jethro@...tanix.com>,
        akpm@...ux-foundation.org, andriy.shevchenko@...ux.intel.com,
        asapek@...gle.com, cedric.xing@...el.com, chenalexchen@...gle.com,
        conradparker@...gle.com, cyhanish@...gle.com,
        dave.hansen@...el.com, haitao.huang@...el.com,
        josh@...htriplett.org, kai.huang@...el.com, kai.svahn@...el.com,
        kmoy@...gle.com, ludloff@...gle.com, luto@...nel.org,
        nhorman@...hat.com, npmccallum@...hat.com, puiterwijk@...hat.com,
        rientjes@...gle.com, tglx@...utronix.de, yaozhangx@...gle.com
Subject: Re: [PATCH v33 03/21] x86/mm: x86/sgx: Signal SIGSEGV with PF_SGX

On Thu, Jun 25, 2020 at 10:59:31AM +0200, Borislav Petkov wrote:
> On Thu, Jun 18, 2020 at 01:08:25AM +0300, Jarkko Sakkinen wrote:
> > From: Sean Christopherson <sean.j.christopherson@...el.com>
> > 
> > Include SGX bit to the PF error codes and throw SIGSEGV with PF_SGX when
> > a #PF with SGX set happens.
> > 
> > CPU throws a #PF with the SGX bit in the event of Enclave Page Cache Map
> 				   ^
> 				   set
> 
> > (EPCM) conflict. The EPCM is a CPU-internal table, which describes the
> > properties for a enclave page. Enclaves are measured and signed software
> > entities, which SGX hosts. [1]
> > 
> > Although the primary purpose of the EPCM conflict checks  is to prevent
> > malicious accesses to an enclave, an illegit access can happen also for
> > legit reasons.
> > 
> > All SGX reserved memory, including EPCM is encrypted with a transient
> > key that does not survive from the power transition. Throwing a SIGSEGV
> > allows user space software react when this happens (e.g. rec-create the
> 			    ^
> 			    to				   recreate
> 
> > enclave, which was invalidated).
> > 
> > [1] Intel SDM: 36.5.1 Enclave Page Cache Map (EPCM)
> > 
> > Acked-by: Jethro Beekman <jethro@...tanix.com>
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> > ---
> >  arch/x86/include/asm/traps.h |  1 +
> >  arch/x86/mm/fault.c          | 13 +++++++++++++
> >  2 files changed, 14 insertions(+)
> > 
> > diff --git a/arch/x86/include/asm/traps.h b/arch/x86/include/asm/traps.h
> > index 714b1a30e7b0..ee3617b67bf4 100644
> > --- a/arch/x86/include/asm/traps.h
> > +++ b/arch/x86/include/asm/traps.h
> > @@ -58,5 +58,6 @@ enum x86_pf_error_code {
> >  	X86_PF_RSVD	=		1 << 3,
> >  	X86_PF_INSTR	=		1 << 4,
> >  	X86_PF_PK	=		1 << 5,
> > +	X86_PF_SGX	=		1 << 15,
> 
> Needs to be added to the doc above it.

I ended up with:

 *   bit 5 ==				1: protection keys block access
 *   bit 6 ==				1: inside SGX enclave
 */

/Jarkko