linux-kernel - Re: [PATCH v22 07/24] x86/sgx: Add wrappers for ENCLS leaf functions

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Date:   Fri, 4 Oct 2019 21:56:49 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-sgx@...r.kernel.org, akpm@...ux-foundation.org,
        dave.hansen@...el.com, sean.j.christopherson@...el.com,
        nhorman@...hat.com, npmccallum@...hat.com, serge.ayoun@...el.com,
        shay.katz-zamir@...el.com, haitao.huang@...el.com,
        andriy.shevchenko@...ux.intel.com, tglx@...utronix.de,
        kai.svahn@...el.com, josh@...htriplett.org, luto@...nel.org,
        kai.huang@...el.com, rientjes@...gle.com, cedric.xing@...el.com
Subject: Re: [PATCH v22 07/24] x86/sgx: Add wrappers for ENCLS leaf functions

On Fri, Oct 04, 2019 at 11:45:13AM +0200, Borislav Petkov wrote:
> On Tue, Sep 03, 2019 at 05:26:38PM +0300, Jarkko Sakkinen wrote:
> > ENCLS is a ring 0 instruction that contains a set of leaf functions for
> > managing enclaves [1]. Enclaves SGX hosted measured and signed software
> > entities, which are protected by asserting the outside memory accesses and
> > memory encryption.
> > 
> > Add a two-layer macro system along with an encoding scheme to allow
> > wrappers to return trap numbers along ENCLS-specific error codes. The
> > bottom layer of the macro system splits between the leafs that return an
> > error code and those that do not. The second layer generates the correct
> > input/output annotations based on the number of operands for each leaf
> > function.
> > 
> > [1] Intel SDM: 36.6 ENCLAVE INSTRUCTIONS AND INTEL®
> > 
> > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> 
> This SOB needs to come...
> 
> > Co-developed-by: Sean Christopherson <sean.j.christopherson@...el.com>
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> 
> <--- ... here.

This issue might persists in a few commits. I'll go through all of
them.

> 
> > +/**
> > + * ENCLS_FAULT_FLAG - flag signifying an ENCLS return code is a trapnr
> > + *
> > + * ENCLS has its own (positive value) error codes and also generates
> > + * ENCLS specific #GP and #PF faults.  And the ENCLS values get munged
> > + * with system error codes as everything percolates back up the stack.
> > + * Unfortunately (for us), we need to precisely identify each unique
> > + * error code, e.g. the action taken if EWB fails varies based on the
> > + * type of fault and on the exact SGX error code, i.e. we can't simply
> > + * convert all faults to -EFAULT.
> > + *
> > + * To make all three error types coexist, we set bit 30 to identify an
> > + * ENCLS fault.  Bit 31 (technically bits N:31) is used to differentiate
> > + * between positive (faults and SGX error codes) and negative (system
> > + * error codes) values.
> > + */
> > +#define ENCLS_FAULT_FLAG 0x40000000
> 
> BIT(30)
> 
> > +
> > +/**
> > + * Retrieve the encoded trapnr from the specified return code.
> > + */
> > +#define ENCLS_TRAPNR(r) ((r) & ~ENCLS_FAULT_FLAG)
> > +
> > +/* Issue a WARN() about an ENCLS leaf. */
> > +#define ENCLS_WARN(r, name) {						\
> > +	do {								\
> > +		int _r = (r);						\
> > +		WARN(_r, "sgx: %s returned %d (0x%x)\n", (name), _r,	\
> > +		     _r);						\
> 
> Let that line stick out a bit:
> 
> 		WARN(_r, "sgx: %s returned %d (0x%x)\n", (name), _r, _r); \
> 
> > +	} while (0);							\
> > +}
> > +
> > +/**
> > + * encls_faulted() - Check if ENCLS leaf function faulted
> > + * @ret:	the return value of an ENCLS leaf function call
> > + *
> > + * Return: true if the fault flag is set
> > + */
> > +static inline bool encls_faulted(int ret)
> > +{
> > +	return (ret & ENCLS_FAULT_FLAG) != 0;
> 
> 	return ret & ENCLS_FAULT_FLAG;

Great, thanks once more for great review comments. Highly appreciated.

/Jarkko