Apply by doing:
        cd /usr/src
        patch -p0 < 012_copy.patch

And then rebuild your kernel.

Index: sys/arch/amd64/amd64/copy.S
===================================================================
RCS file: /cvs/src/sys/arch/amd64/amd64/copy.S,v
retrieving revision 1.1
retrieving revision 1.1.6.1
diff -u -p -U20 -r1.1 -r1.1.6.1
--- sys/arch/amd64/amd64/copy.S	28 Jan 2004 01:39:38 -0000	1.1
+++ sys/arch/amd64/amd64/copy.S	16 Mar 2005 23:49:00 -0000	1.1.6.1
@@ -190,40 +190,41 @@ NENTRY(copy_efault)
 	movq	$EFAULT,%rax
 
 NENTRY(copy_fault)
 	movq	CPUVAR(CURPCB),%rdx
 	popq	PCB_ONFAULT(%rdx)
 	ret
 
 ENTRY(copyoutstr)
 	xchgq	%rdi,%rsi
 	movq	%rdx,%r8
 	movq	%rcx,%r9
 
 5:	movq	CPUVAR(CURPCB),%rax
 	leaq	_C_LABEL(copystr_fault)(%rip),%r11
 	movq	%r11,PCB_ONFAULT(%rax)
 	/*
 	 * Get min(%rdx, VM_MAXUSER_ADDRESS-%rdi).
 	 */
 	movq	$VM_MAXUSER_ADDRESS,%rax
 	subq	%rdi,%rax
+	jc	_C_LABEL(copystr_efault)
 	cmpq	%rdx,%rax
 	jae	1f
 	movq	%rax,%rdx
 	movq	%rax,%r8
 
 1:	incq	%rdx
 	cld
 
 1:	decq	%rdx
 	jz	2f
 	lodsb
 	stosb
 	testb	%al,%al
 	jnz	1b
 
 	/* Success -- 0 byte reached. */
 	decq	%rdx
 	xorq	%rax,%rax
 	jmp	copystr_return
 
@@ -231,40 +232,41 @@ ENTRY(copyoutstr)
 	movq	$VM_MAXUSER_ADDRESS,%r11
 	cmpq	%r11,%rdi
 	jae	_C_LABEL(copystr_efault)
 	movq	$ENAMETOOLONG,%rax
 	jmp	copystr_return
 
 ENTRY(copyinstr)
 	xchgq	%rdi,%rsi
 	movq	%rdx,%r8
 	movq	%rcx,%r9
 
 	movq	CPUVAR(CURPCB),%rcx
 	leaq	_C_LABEL(copystr_fault)(%rip),%r11
 	movq	%r11,PCB_ONFAULT(%rcx)
 
 	/*
 	 * Get min(%rdx, VM_MAXUSER_ADDRESS-%rsi).
 	 */
 	movq	$VM_MAXUSER_ADDRESS,%rax
 	subq	%rsi,%rax
+	jc	_C_LABEL(copystr_efault)
 	cmpq	%rdx,%rax
 	jae	1f
 	movq	%rax,%rdx
 	movq	%rax,%r8
 
 1:	incq	%rdx
 	cld
 
 1:	decq	%rdx
 	jz	2f
 	lodsb
 	stosb
 	testb	%al,%al
 	jnz	1b
 
 	/* Success -- 0 byte reached. */
 	decq	%rdx
 	xorq	%rax,%rax
 	jmp	copystr_return