Linux-Sgx Archive on lore.kernel.org
 help / color / Atom feed
From: "Xing, Cedric" <cedric.xing@intel.com>
To: Sean Christopherson <sean.j.christopherson@intel.com>,
	Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc: linux-sgx@vger.kernel.org
Subject: Re: [PATCH for_v23 4/5] x86/vdso: sgx: Reorder params to callback to improve readability
Date: Wed, 16 Oct 2019 15:24:54 -0700
Message-ID: <34e9c245-34d5-fbd3-6d50-deac4adc29f6@intel.com> (raw)
In-Reply-To: <20191011004059.28581-5-sean.j.christopherson@intel.com>

On 10/10/2019 5:40 PM, Sean Christopherson wrote:
> Swap @ret and @ursp in the callback prototype so that the output from
> the vDSO itself, @ret and @e, are grouped together.  Having the first
> N parameters all share a type also makes the prototype easier to parse
> by (some) humans.  And, passing @ursp via register saves one whole
> MOV instruction!
> 
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
>   arch/x86/entry/vdso/vsgx_enter_enclave.S | 16 +++++++---------
>   arch/x86/include/uapi/asm/sgx.h          | 10 +++++-----
>   2 files changed, 12 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/x86/entry/vdso/vsgx_enter_enclave.S b/arch/x86/entry/vdso/vsgx_enter_enclave.S
> index 3dd22780b7ef..94f613b53b13 100644
> --- a/arch/x86/entry/vdso/vsgx_enter_enclave.S
> +++ b/arch/x86/entry/vdso/vsgx_enter_enclave.S
> @@ -134,23 +134,21 @@ ENTRY(__vdso_sgx_enter_enclave)
>   	jmp	.Lhandle_exit
>   
>   .Linvoke_userspace_handler:
> +	/* Pass the untrusted RSP (at exit) to the callback via %rcx. */
> +	mov	%rsp, %rcx
> +
>   	/*
> -	 * Align stack per x86_64 ABI. Save the original %rsp in %rbx to be
> -	 * restored after the callback returns.  Note, %rsp needs to be 16-byte
> -	 * aligned _after_ pushing the three parameters on the stack.
> +	 * Align stack per x86_64 ABI. Note, %rsp needs to be 16-byte aligned
> +	 * _after_ pushing the three parameters on the stack.
>   	 */
> -	mov	%rsp, %rbx

Per x86_64 ABI, %rcx is _not_ preserved across function call. How are 
you going to restore the stack after callback returns?

>   	and	$-0x10, %rsp
>   	sub	$0x8, %rsp

Usually compilers would just use a 1-byte "push" instead of a 4-byte 
"sub" instruction here.

>   
> -	/* Push @e, u_rsp and @tcs as parameters to the callback. */
> +	/* Push @e, the "return" value and @tcs as params to the callback. */
>   	push	0x18(%rbp)
> -	push	%rbx
> +	push	%rax
>   	push	0x10(%rbp)
>   
> -	/* Pass the "return" value to the callback via %rcx. */
> -	mov	%eax, %ecx
> -
>   	/* Clear RFLAGS.DF per x86_64 ABI */
>   	cld
>   
> diff --git a/arch/x86/include/uapi/asm/sgx.h b/arch/x86/include/uapi/asm/sgx.h
> index 255392f5054f..95f69f938b58 100644
> --- a/arch/x86/include/uapi/asm/sgx.h
> +++ b/arch/x86/include/uapi/asm/sgx.h
> @@ -88,16 +88,16 @@ struct sgx_enclave_exception {
>    * @rdi:	RDI at the time of enclave exit
>    * @rsi:	RSI at the time of enclave exit
>    * @rdx:	RDX at the time of enclave exit
> - * @ret:	0 on success (EEXIT), -EFAULT on an exception
> + * @ursp:	RSP at the time of enclave exit (untrusted stack)
>    * @r8:		R8 at the time of enclave exit
>    * @r9:		R9 at the time of enclave exit
>    * @tcs:	Thread Control Structure used to enter enclave
> - * @ursp:	RSP at the time of enclave exit
> + * @ret:	0 on success (EEXIT), -EFAULT on an exception
>    * @e:		Pointer to struct sgx_enclave_exception (as provided by caller)
>    */
> -typedef int (*sgx_enclave_exit_handler_t)(long rdi, long rsi, long rdx, int ret,
> -					  long r8, long r9, void *tcs,
> -					  long ursp,
> +typedef int (*sgx_enclave_exit_handler_t)(long rdi, long rsi, long rdx,
> +					  long ursp, long r8, long r9,
> +					  void *tcs, int ret,
>   					  struct sgx_enclave_exception *e);
>   
>   #endif /* _UAPI_ASM_X86_SGX_H */
> 

  reply index

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-11  0:40 [PATCH for_v23 0/5] x86/vdso: sgx: Bug fixes Sean Christopherson
2019-10-11  0:40 ` [PATCH for_v23 1/5] x86/vdso: sgx: Fix misaligned stack bug when invoking exit handler Sean Christopherson
2019-10-11  0:40 ` [PATCH for_v23 2/5] selftests/x86/sgx: Add check to verify exit handler stack alignment Sean Christopherson
2019-10-14 21:09   ` Jarkko Sakkinen
2019-10-14 21:14     ` Jarkko Sakkinen
2019-10-11  0:40 ` [PATCH for_v23 3/5] x86/vdso: sgx: Fix unwinder support Sean Christopherson
2019-10-16 22:25   ` Xing, Cedric
2019-10-11  0:40 ` [PATCH for_v23 4/5] x86/vdso: sgx: Reorder params to callback to improve readability Sean Christopherson
2019-10-16 22:24   ` Xing, Cedric [this message]
2019-10-16 23:06     ` Sean Christopherson
2019-10-11  0:40 ` [PATCH for_v23 5/5] selftests/x86/sgx: Update the callbacks function parameters Sean Christopherson
2019-10-14 21:27 ` [PATCH for_v23 0/5] x86/vdso: sgx: Bug fixes Jarkko Sakkinen

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=34e9c245-34d5-fbd3-6d50-deac4adc29f6@intel.com \
    --to=cedric.xing@intel.com \
    --cc=jarkko.sakkinen@linux.intel.com \
    --cc=linux-sgx@vger.kernel.org \
    --cc=sean.j.christopherson@intel.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-Sgx Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-sgx/0 linux-sgx/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-sgx linux-sgx/ https://lore.kernel.org/linux-sgx \
		linux-sgx@vger.kernel.org
	public-inbox-index linux-sgx

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-sgx


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git