linux-kernel - [PATCH] x86/entry/x32: Check top 32 bits of syscall number on the fast path

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Message-ID: <20160418004731.GB3348@decadent.org.uk>
Date:	Mon, 18 Apr 2016 01:47:31 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] x86/entry/x32: Check top 32 bits of syscall number on the
 fast path

We've always masked off the top 32 bits when x32 is enabled, but
hopefully no-one relies on that.  Now that the slow path is in C, we
check all the bits there, regardless of whether x32 is enabled.  Let's
make the fast path consistent with it.

Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
Cc: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/entry/entry_64.S | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 858b555e274b..17ba2ca9b24d 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -190,12 +190,10 @@ entry_SYSCALL_64_fastpath:
 	 */
 	TRACE_IRQS_ON
 	ENABLE_INTERRUPTS(CLBR_NONE)
-#if __SYSCALL_MASK == ~0
-	cmpq	$__NR_syscall_max, %rax
-#else
-	andl	$__SYSCALL_MASK, %eax
-	cmpl	$__NR_syscall_max, %eax
+#if __SYSCALL_MASK != ~0
+	andq	$__SYSCALL_MASK, %rax
 #endif
+	cmpq	$__NR_syscall_max, %rax
 	ja	1f				/* return -ENOSYS (already in pt_regs->ax) */
 	movq	%r10, %rcx
 

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