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From: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To: linux-sgx@vger.kernel.org
Cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
	x86@kernel.org, Haitao Huang <haitao.huang@linux.intel.com>,
	Sean Christopherson <sean.j.christopherson@intel.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Andy Lutomirski <luto@amacapital.net>,
	Cedric Xing <cedric.xing@intel.com>
Subject: [PATCH] x86/vdso: Remove retpoline from SGX vDSO call
Date: Wed, 30 Sep 2020 17:01:08 +0300	[thread overview]
Message-ID: <20200930140108.48075-1-jarkko.sakkinen@linux.intel.com> (raw)

The user handler, which can be optionally used to handle enclave
exceptions, is always the same global handler provided by the SGX
runtime, who wants to use such a handler instead returning on exception.

Thus, there is no any non-deterministic branch prediction happening.
The code path is always the same and never change. Obviously, you could
change it all the time purposely but for any sane real-world use that
would not make any sense.

Thus, remove retpoline wrapping.

Cc: x86@kernel.org
Cc: Haitao Huang <haitao.huang@linux.intel.com>
CC: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Cedric Xing <cedric.xing@intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
---
 arch/x86/entry/vdso/vsgx.S | 9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/arch/x86/entry/vdso/vsgx.S b/arch/x86/entry/vdso/vsgx.S
index 8f8190ab9ed5..5f65bb22014f 100644
--- a/arch/x86/entry/vdso/vsgx.S
+++ b/arch/x86/entry/vdso/vsgx.S
@@ -129,7 +129,7 @@ SYM_FUNC_START(__vdso_sgx_enter_enclave)
 
 	/* Load the callback pointer to %rax and invoke it via retpoline. */
 	mov	SGX_ENCLAVE_RUN_USER_HANDLER(%rax), %rax
-	call	.Lretpoline
+	call	*%rax
 
 	/* Undo the post-exit %rsp adjustment. */
 	lea	0x10(%rsp, %rbx), %rsp
@@ -143,13 +143,6 @@ SYM_FUNC_START(__vdso_sgx_enter_enclave)
 	jle	.Lout
 	jmp	.Lenter_enclave
 
-.Lretpoline:
-	call	2f
-1:	pause
-	lfence
-	jmp	1b
-2:	mov	%rax, (%rsp)
-	ret
 	.cfi_endproc
 
 _ASM_VDSO_EXTABLE_HANDLE(.Lenclu_eenter_eresume, .Lhandle_exception)
-- 
2.25.1


             reply	other threads:[~2020-09-30 14:01 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-30 14:01 Jarkko Sakkinen [this message]
2020-09-30 14:08 ` [PATCH] x86/vdso: Remove retpoline from SGX vDSO call Dave Hansen
2020-09-30 14:20   ` Jarkko Sakkinen
2020-09-30 14:33     ` Dave Hansen
2020-09-30 15:28       ` Jarkko Sakkinen
2020-09-30 15:43         ` Sean Christopherson
2020-09-30 16:28           ` Dave Hansen
2020-09-30 17:01             ` Jethro Beekman
2020-09-30 18:09               ` Andrew Cooper
2020-09-30 19:25                 ` Jarkko Sakkinen
2020-09-30 20:45                   ` Xing, Cedric
2020-09-30 21:22                     ` Jarkko Sakkinen
2020-09-30 21:36                       ` Jarkko Sakkinen
2020-09-30 21:46                         ` Dave Hansen
2020-09-30 23:41                           ` Jarkko Sakkinen
2020-09-30 16:38           ` Jarkko Sakkinen

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