linux-kernel - Re: [PATCH v36 03/24] x86/mm: x86/sgx: Signal SIGSEGV with PF

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Date:   Thu, 20 Aug 2020 17:31:14 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
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 v36 03/24] x86/mm: x86/sgx: Signal SIGSEGV with PF_SGX

On Thu, Jul 16, 2020 at 04:52:42PM +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 set in the event of Enclave Page Cache Map
> (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 to react when this happens (e.g. recreate the 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 | 14 ++++++++------
>  arch/x86/mm/fault.c          | 13 +++++++++++++
>  2 files changed, 21 insertions(+), 6 deletions(-)

Reviewed-by: Borislav Petkov <bp@...e.de>

-- 
Regards/Gruss,
    Boris.

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