Re: [PATCH v3 13/25] x86/sgx: Add helpers to expose ECREATE and EINIT to KVM

[Kai Huang <kai.huang@intel.com>]

On Tue, 6 Apr 2021 19:08:58 +0200 Borislav Petkov wrote:
> On Tue, Apr 06, 2021 at 09:41:52PM +1200, Kai Huang wrote:
> > > Ok, I'll make the changes and you can redo the KVM rest ontop.
> > > 
> > 
> > Thank you!
> 
> I.e., something like this:

Looks good. I'll update KVM part patches based on this one. 

Thanks.

> 
> ---
> From: Sean Christopherson <sean.j.christopherson@intel.com>
> Date: Fri, 19 Mar 2021 20:23:08 +1300
> Subject: [PATCH] x86/sgx: Add helpers to expose ECREATE and EINIT to KVM
> 
> The host kernel must intercept ECREATE to impose policies on guests, and
> intercept EINIT to be able to write guest's virtual SGX_LEPUBKEYHASH MSR
> values to hardware before running guest's EINIT so it can run correctly
> according to hardware behavior.
> 
> Provide wrappers around __ecreate() and __einit() to hide the ugliness
> of overloading the ENCLS return value to encode multiple error formats
> in a single int.  KVM will trap-and-execute ECREATE and EINIT as part
> of SGX virtualization, and reflect ENCLS execution result to guest by
> setting up guest's GPRs, or on an exception, injecting the correct fault
> based on return value of __ecreate() and __einit().
> 
> Use host userspace addresses (provided by KVM based on guest physical
> address of ENCLS parameters) to execute ENCLS/EINIT when possible.
> Accesses to both EPC and memory originating from ENCLS are subject to
> segmentation and paging mechanisms.  It's also possible to generate
> kernel mappings for ENCLS parameters by resolving PFN but using
> __uaccess_xx() is simpler.
> 
>  [ bp: Return early if the __user memory accesses fail. ]
> 
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Signed-off-by: Kai Huang <kai.huang@intel.com>
> Signed-off-by: Borislav Petkov <bp@suse.de>
> Acked-by: Jarkko Sakkinen <jarkko@kernel.org>
> Link: https://lkml.kernel.org/r/20e09daf559aa5e9e680a0b4b5fba940f1bad86e.1616136308.git.kai.huang@intel.com
> ---
>  arch/x86/include/asm/sgx.h     |   7 ++
>  arch/x86/kernel/cpu/sgx/virt.c | 117 +++++++++++++++++++++++++++++++++
>  2 files changed, 124 insertions(+)
> 
> diff --git a/arch/x86/include/asm/sgx.h b/arch/x86/include/asm/sgx.h
> index 3b025afec0a7..954042e04102 100644
> --- a/arch/x86/include/asm/sgx.h
> +++ b/arch/x86/include/asm/sgx.h
> @@ -365,4 +365,11 @@ struct sgx_sigstruct {
>   * comment!
>   */
>  
> +#ifdef CONFIG_X86_SGX_KVM
> +int sgx_virt_ecreate(struct sgx_pageinfo *pageinfo, void __user *secs,
> +		     int *trapnr);
> +int sgx_virt_einit(void __user *sigstruct, void __user *token,
> +		   void __user *secs, u64 *lepubkeyhash, int *trapnr);
> +#endif
> +
>  #endif /* _ASM_X86_SGX_H */
> diff --git a/arch/x86/kernel/cpu/sgx/virt.c b/arch/x86/kernel/cpu/sgx/virt.c
> index 259cc46ad78c..7d221eac716a 100644
> --- a/arch/x86/kernel/cpu/sgx/virt.c
> +++ b/arch/x86/kernel/cpu/sgx/virt.c
> @@ -257,3 +257,120 @@ int __init sgx_vepc_init(void)
>  
>  	return misc_register(&sgx_vepc_dev);
>  }
> +
> +/**
> + * sgx_virt_ecreate() - Run ECREATE on behalf of guest
> + * @pageinfo:	Pointer to PAGEINFO structure
> + * @secs:	Userspace pointer to SECS page
> + * @trapnr:	trap number injected to guest in case of ECREATE error
> + *
> + * Run ECREATE on behalf of guest after KVM traps ECREATE for the purpose
> + * of enforcing policies of guest's enclaves, and return the trap number
> + * which should be injected to guest in case of any ECREATE error.
> + *
> + * Return:
> + * -  0:	ECREATE was successful.
> + * - <0:	on error.
> + */
> +int sgx_virt_ecreate(struct sgx_pageinfo *pageinfo, void __user *secs,
> +		     int *trapnr)
> +{
> +	int ret;
> +
> +	/*
> +	 * @secs is an untrusted, userspace-provided address.  It comes from
> +	 * KVM and is assumed to be a valid pointer which points somewhere in
> +	 * userspace.  This can fault and call SGX or other fault handlers when
> +	 * userspace mapping @secs doesn't exist.
> +	 *
> +	 * Add a WARN() to make sure @secs is already valid userspace pointer
> +	 * from caller (KVM), who should already have handled invalid pointer
> +	 * case (for instance, made by malicious guest).  All other checks,
> +	 * such as alignment of @secs, are deferred to ENCLS itself.
> +	 */
> +	if (WARN_ON_ONCE(!access_ok(secs, PAGE_SIZE)))
> +		return -EINVAL;
> +
> +	__uaccess_begin();
> +	ret = __ecreate(pageinfo, (void *)secs);
> +	__uaccess_end();
> +
> +	if (encls_faulted(ret)) {
> +		*trapnr = ENCLS_TRAPNR(ret);
> +		return -EFAULT;
> +	}
> +
> +	/* ECREATE doesn't return an error code, it faults or succeeds. */
> +	WARN_ON_ONCE(ret);
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(sgx_virt_ecreate);
> +
> +static int __sgx_virt_einit(void __user *sigstruct, void __user *token,
> +			    void __user *secs)
> +{
> +	int ret;
> +
> +	/*
> +	 * Make sure all userspace pointers from caller (KVM) are valid.
> +	 * All other checks deferred to ENCLS itself.  Also see comment
> +	 * for @secs in sgx_virt_ecreate().
> +	 */
> +#define SGX_EINITTOKEN_SIZE	304
> +	if (WARN_ON_ONCE(!access_ok(sigstruct, sizeof(struct sgx_sigstruct)) ||
> +			 !access_ok(token, SGX_EINITTOKEN_SIZE) ||
> +			 !access_ok(secs, PAGE_SIZE)))
> +		return -EINVAL;
> +
> +	__uaccess_begin();
> +	ret = __einit((void *)sigstruct, (void *)token, (void *)secs);
> +	__uaccess_end();
> +
> +	return ret;
> +}
> +
> +/**
> + * sgx_virt_einit() - Run EINIT on behalf of guest
> + * @sigstruct:		Userspace pointer to SIGSTRUCT structure
> + * @token:		Userspace pointer to EINITTOKEN structure
> + * @secs:		Userspace pointer to SECS page
> + * @lepubkeyhash:	Pointer to guest's *virtual* SGX_LEPUBKEYHASH MSR values
> + * @trapnr:		trap number injected to guest in case of EINIT error
> + *
> + * Run EINIT on behalf of guest after KVM traps EINIT. If SGX_LC is available
> + * in host, SGX driver may rewrite the hardware values at wish, therefore KVM
> + * needs to update hardware values to guest's virtual MSR values in order to
> + * ensure EINIT is executed with expected hardware values.
> + *
> + * Return:
> + * -  0:	EINIT was successful.
> + * - <0:	on error.
> + */
> +int sgx_virt_einit(void __user *sigstruct, void __user *token,
> +		   void __user *secs, u64 *lepubkeyhash, int *trapnr)
> +{
> +	int ret;
> +
> +	if (!cpu_feature_enabled(X86_FEATURE_SGX_LC)) {
> +		ret = __sgx_virt_einit(sigstruct, token, secs);
> +	} else {
> +		preempt_disable();
> +
> +		sgx_update_lepubkeyhash(lepubkeyhash);
> +
> +		ret = __sgx_virt_einit(sigstruct, token, secs);
> +		preempt_enable();
> +	}
> +
> +	/* Propagate up the error from the WARN_ON_ONCE in __sgx_virt_einit() */
> +	if (ret == -EINVAL)
> +		return ret;
> +
> +	if (encls_faulted(ret)) {
> +		*trapnr = ENCLS_TRAPNR(ret);
> +		return -EFAULT;
> +	}
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(sgx_virt_einit);
> -- 
> 2.29.2
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette