Re: [PATCH v19 13/27] x86/sgx: Add wrappers for ENCLS leaf functions

[Sean Christopherson <sean.j.christopherson@intel.com>]

On Sun, Mar 17, 2019 at 11:14:42PM +0200, Jarkko Sakkinen wrote:
> ENCLS is an umbrella instruction for a variety of cpl0 SGX functions.
> The ENCLS function that is executed is specified in EAX, with each
> function potentially having more leaf-specific operands beyond EAX.
> ENCLS introduces its own (positive value) error codes that (some)
> leafs use to return failure information in EAX.  Leafs that return
> an error code also modify RFLAGS.  And finally, ENCLS generates
> ENCLS-specific non-fatal #GPs and #PFs, i.e. a bug-free kernel may
> encounter faults on ENCLS that must be handled gracefully.
> 
> Because of the complexity involved in encoding ENCLS and handling its
> assortment of failure paths, executing any given leaf is not a simple
> matter of emitting ENCLS.
> 
> To enable adding support for ENCLS leafs with minimal fuss, 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.
> 
> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
> Co-developed-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
>  arch/x86/kernel/cpu/sgx/Makefile |   2 +-
>  arch/x86/kernel/cpu/sgx/encls.c  |  21 +++
>  arch/x86/kernel/cpu/sgx/encls.h  | 244 +++++++++++++++++++++++++++++++
>  3 files changed, 266 insertions(+), 1 deletion(-)
>  create mode 100644 arch/x86/kernel/cpu/sgx/encls.c
>  create mode 100644 arch/x86/kernel/cpu/sgx/encls.h
> 
> diff --git a/arch/x86/kernel/cpu/sgx/Makefile b/arch/x86/kernel/cpu/sgx/Makefile
> index b666967fd570..20ce33655ff4 100644
> --- a/arch/x86/kernel/cpu/sgx/Makefile
> +++ b/arch/x86/kernel/cpu/sgx/Makefile
> @@ -1 +1 @@
> -obj-y += main.o
> +obj-y += main.o encls.o
> diff --git a/arch/x86/kernel/cpu/sgx/encls.c b/arch/x86/kernel/cpu/sgx/encls.c
> new file mode 100644
> index 000000000000..5045f1365e07
> --- /dev/null
> +++ b/arch/x86/kernel/cpu/sgx/encls.c
> @@ -0,0 +1,21 @@
> +#include <asm/cpufeature.h>
> +#include <asm/traps.h>
> +#include "encls.h"
> +#include "sgx.h"
> +
> +/**
> + * encls_failed() - Check if an ENCLS leaf function failed
> + * @ret:	the return value of an ENCLS leaf function call
> + *
> + * Check if an ENCLS leaf function failed. This is a condition where the leaf
> + * function causes a fault that is not caused by an EPCM conflict.

"conflict" is a poor word choice.  The SDM's refers to EPC conflicts as
trying to concurrently access an EPC page from multiple logical CPUs.

Maybe "EPCM violation" or simply "EPCM fault"?

> + *
> + * Return: true if there was a fault other than an EPCM conflict
> + */
> +bool encls_failed(int ret)

I really dislike this name.  IMO, "encls_failed" is inaccurate and to some
extent an unnecessary abstraction.  Regardless of why it faulted, the
ENCLS instruction "failed".  Just because the fault originated in the EPCM
doesn't mean the instruction magically succeeded.

What if we inverted the logic, i.e. to identify EPCM violations?  And
rename encls_fault() to is_encls_fault(), and encls_returned_code()
to is_sgx_error_code().  E.g.:

bool is_epcm_violation(int ret)
{
	return is_encls_fault(ret) && ENCLS_TRAPNR(ret) == epcm_trapnr;
}

Then the usage becomes:

	if (is_sgx_error_code(ret) ||
	    (is_encls_fault(ret) && !is_epcm_violation(ret))
		blah blah blah

The usage is more verbose, but explicitly clear.

> +{
> +	int epcm_trapnr = boot_cpu_has(X86_FEATURE_SGX2) ?
> +			  X86_TRAP_PF : X86_TRAP_GP;

epcm_trapnr should be calculated once during init.

> +
> +	return encls_faulted(ret) && ENCLS_TRAPNR(ret) != epcm_trapnr;
> +}

Why isn't this function inlined in sgx.h?

> diff --git a/arch/x86/kernel/cpu/sgx/encls.h b/arch/x86/kernel/cpu/sgx/encls.h
> new file mode 100644
> index 000000000000..aea3b9d09936
> --- /dev/null
> +++ b/arch/x86/kernel/cpu/sgx/encls.h
> @@ -0,0 +1,244 @@
> +/* SPDX-License-Identifier: (GPL-2.0 OR BSD-3-Clause) */
> +#ifndef _X86_ENCLS_H
> +#define _X86_ENCLS_H
> +
> +#include <linux/bitops.h>
> +#include <linux/err.h>
> +#include <linux/io.h>
> +#include <linux/rwsem.h>
> +#include <linux/types.h>
> +#include <asm/asm.h>
> +#include "arch.h"
> +
> +/**
> + * 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
> +
> +/**
> + * Retrieve the encoded trapnr from the specified return code.
> + */
> +#define ENCLS_TRAPNR(r) ((r) & ~ENCLS_FAULT_FLAG)

I honestly can't remember, is there a reason ENCLS_TRAPNR is still a macro
and not an inline function?

> +
> +/* Issue a WARN() about an ENCLS leaf. */

If you're going to bother with a comment, might as well document the
interesting part, i.e. why we print both the decimal and hexidecimal
formats, which is the reason this macro exists at all.

> +#define ENCLS_WARN(r, name) {						\

Taking the warn condition and the raw error code in a single parameter
makes the call sites ugly, e.g.

	if (ret) {
		if (encls_failed(ret))
			ENCLS_WARN(ret, "EADD");
		return false;
	}

If the macro is instead something like:

#define ENCLS_WARN(do_warn, r, name) \
	WARN(w, "sgx: %s returned %d (0x%x)\n", (name), (r), (r); \

then we can drop the do-while wrapping and the callers are a little less
ugly, e.g.:

	if (ret) {
		ENCLS_WARN(encls_failed(ret), ret, "EADD");
		return ret;
	}


Or with the is_epcm_violation() variant:

	if (ret) {
		ENCLS_WARN(is_encls_fault(ret) && !is_epcm_violation(ret),
			   ret, "EADD");
		return ret;
	}

> +	do {								\
> +		int _r = (r);						\
> +		WARN(_r, "sgx: %s returned %d (0x%x)\n", (name), _r,	\
> +		     _r);						\

There's no need to wrap this, just add spaces before the '\'.

> +	} 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;
> +}
> +
> +/**
> + * encls_returned_code() - Check if an ENCLS leaf function returned a code
> + * @ret:	the return value of an ENCLS leaf function call
> + *
> + * Check if an ENCLS leaf function returned an error or information code.
> + *
> + * Return: true if there was a fault other than an EPCM conflict
> + */
> +static inline bool encls_returned_code(int ret)
> +{
> +	return !encls_faulted(ret) && ret;

Nit: IMO checking for non-zero ret should be first, both from a readability
     perspective and from a code generation perspective.

> +}
> +
> +bool encls_failed(int ret);
> +
> +/**
> + * __encls_ret_N - encode an ENCLS leaf that returns an error code in EAX
> + * @rax:	leaf number
> + * @inputs:	asm inputs for the leaf
> + *
> + * Emit assembly for an ENCLS leaf that returns an error code, e.g. EREMOVE.
> + * And because SGX isn't complex enough as it is, leafs that return an error
> + * code also modify flags.
> + *
> + * Return:
> + *	0 on success,
> + *	SGX error code on failure
> + */
> +#define __encls_ret_N(rax, inputs...)				\
> +	({							\
> +	int ret;						\
> +	asm volatile(						\
> +	"1: .byte 0x0f, 0x01, 0xcf;\n\t"			\
> +	"2:\n"							\
> +	".section .fixup,\"ax\"\n"				\
> +	"3: orl $"__stringify(ENCLS_FAULT_FLAG)",%%eax\n"	\
> +	"   jmp 2b\n"						\
> +	".previous\n"						\
> +	_ASM_EXTABLE_FAULT(1b, 3b)				\
> +	: "=a"(ret)						\
> +	: "a"(rax), inputs					\
> +	: "memory", "cc");					\
> +	ret;							\
> +	})
> +
> +#define __encls_ret_1(rax, rcx)		\
> +	({				\
> +	__encls_ret_N(rax, "c"(rcx));	\
> +	})
> +
> +#define __encls_ret_2(rax, rbx, rcx)		\
> +	({					\
> +	__encls_ret_N(rax, "b"(rbx), "c"(rcx));	\
> +	})
> +
> +#define __encls_ret_3(rax, rbx, rcx, rdx)			\
> +	({							\
> +	__encls_ret_N(rax, "b"(rbx), "c"(rcx), "d"(rdx));	\
> +	})
> +
> +/**
> + * __encls_N - encode an ENCLS leaf that doesn't return an error code
> + * @rax:	leaf number
> + * @rbx_out:	optional output variable
> + * @inputs:	asm inputs for the leaf
> + *
> + * Emit assembly for an ENCLS leaf that does not return an error code,
> + * e.g. ECREATE.  Leaves without error codes either succeed or fault.
> + * @rbx_out is an optional parameter for use by EDGBRD, which returns
> + * the the requested value in RBX.
> + *
> + * Return:
> + *   0 on success,
> + *   trapnr with ENCLS_FAULT_FLAG set on fault
> + */
> +#define __encls_N(rax, rbx_out, inputs...)			\
> +	({							\
> +	int ret;						\
> +	asm volatile(						\
> +	"1: .byte 0x0f, 0x01, 0xcf;\n\t"			\
> +	"   xor %%eax,%%eax;\n"					\
> +	"2:\n"							\
> +	".section .fixup,\"ax\"\n"				\
> +	"3: orl $"__stringify(ENCLS_FAULT_FLAG)",%%eax\n"	\
> +	"   jmp 2b\n"						\
> +	".previous\n"						\
> +	_ASM_EXTABLE_FAULT(1b, 3b)				\
> +	: "=a"(ret), "=b"(rbx_out)				\
> +	: "a"(rax), inputs					\
> +	: "memory");						\
> +	ret;							\
> +	})
> +
> +#define __encls_2(rax, rbx, rcx)				\
> +	({							\
> +	unsigned long ign_rbx_out;				\
> +	__encls_N(rax, ign_rbx_out, "b"(rbx), "c"(rcx));	\
> +	})
> +
> +#define __encls_1_1(rax, data, rcx)			\
> +	({						\
> +	unsigned long rbx_out;				\
> +	int ret = __encls_N(rax, rbx_out, "c"(rcx));	\
> +	if (!ret)					\
> +		data = rbx_out;				\
> +	ret;						\
> +	})
> +
> +static inline int __ecreate(struct sgx_pageinfo *pginfo, void *secs)
> +{
> +	return __encls_2(SGX_ECREATE, pginfo, secs);
> +}
> +
> +static inline int __eextend(void *secs, void *addr)
> +{
> +	return __encls_2(SGX_EEXTEND, secs, addr);
> +}
> +
> +static inline int __eadd(struct sgx_pageinfo *pginfo, void *addr)
> +{
> +	return __encls_2(SGX_EADD, pginfo, addr);
> +}
> +
> +static inline int __einit(void *sigstruct, struct sgx_einittoken *einittoken,
> +			  void *secs)
> +{
> +	return __encls_ret_3(SGX_EINIT, sigstruct, secs, einittoken);
> +}
> +
> +static inline int __eremove(void *addr)
> +{
> +	return __encls_ret_1(SGX_EREMOVE, addr);
> +}
> +
> +static inline int __edbgwr(void *addr, unsigned long *data)
> +{
> +	return __encls_2(SGX_EDGBWR, *data, addr);
> +}
> +
> +static inline int __edbgrd(void *addr, unsigned long *data)
> +{
> +	return __encls_1_1(SGX_EDGBRD, *data, addr);
> +}
> +
> +static inline int __etrack(void *addr)
> +{
> +	return __encls_ret_1(SGX_ETRACK, addr);
> +}
> +
> +static inline int __eldu(struct sgx_pageinfo *pginfo, void *addr,
> +			 void *va)
> +{
> +	return __encls_ret_3(SGX_ELDU, pginfo, addr, va);
> +}
> +
> +static inline int __eblock(void *addr)
> +{
> +	return __encls_ret_1(SGX_EBLOCK, addr);
> +}
> +
> +static inline int __epa(void *addr)
> +{
> +	unsigned long rbx = SGX_PAGE_TYPE_VA;
> +
> +	return __encls_2(SGX_EPA, rbx, addr);
> +}
> +
> +static inline int __ewb(struct sgx_pageinfo *pginfo, void *addr,
> +			void *va)
> +{
> +	return __encls_ret_3(SGX_EWB, pginfo, addr, va);
> +}
> +
> +static inline int __eaug(struct sgx_pageinfo *pginfo, void *addr)
> +{
> +	return __encls_2(SGX_EAUG, pginfo, addr);
> +}
> +
> +static inline int __emodpr(struct sgx_secinfo *secinfo, void *addr)
> +{
> +	return __encls_ret_2(SGX_EMODPR, secinfo, addr);
> +}
> +
> +static inline int __emodt(struct sgx_secinfo *secinfo, void *addr)
> +{
> +	return __encls_ret_2(SGX_EMODT, secinfo, addr);
> +}
> +
> +#endif /* _X86_ENCLS_H */
> -- 
> 2.19.1
>