D12023.id32305.diff
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	Index: lib/libc/amd64/sys/Makefile.inc
	===================================================================
	--- lib/libc/amd64/sys/Makefile.inc
	+++ lib/libc/amd64/sys/Makefile.inc
	@@ -1,7 +1,11 @@
	# from: Makefile.inc,v 1.1 1993/09/03 19:04:23 jtc Exp
	# $FreeBSD$

	-SRCS+= amd64_get_fsbase.c amd64_get_gsbase.c amd64_set_fsbase.c \
	+SRCS+= \
	+ amd64_detect_rdfsgsbase.c \
	+ amd64_get_fsbase.c \
	+ amd64_get_gsbase.c \
	+ amd64_set_fsbase.c \
	amd64_set_gsbase.c

	MDASM= vfork.S brk.S cerror.S exect.S getcontext.S \
	Index: lib/libc/amd64/sys/amd64_detect_rdfsgsbase.h
	===================================================================
	--- /dev/null
	+++ lib/libc/amd64/sys/amd64_detect_rdfsgsbase.h
	@@ -0,0 +1,43 @@
	+/*-
	+ * Copyright (c) 2017 The FreeBSD Foundation
	+ * All rights reserved.
	+ *
	+ * This software was developed by Konstantin Belousov <kib@FreeBSD.org>
	+ * under sponsorship from the FreeBSD Foundation.
	+ *
	+ * Redistribution and use in source and binary forms, with or without
	+ * modification, are permitted provided that the following conditions
	+ * are met:
	+ * 1. Redistributions of source code must retain the above copyright
	+ * notice, this list of conditions and the following disclaimer.
	+ * 2. Redistributions in binary form must reproduce the above copyright
	+ * notice, this list of conditions and the following disclaimer in the
	+ * documentation and/or other materials provided with the distribution.
	+ *
	+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
	+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	+ * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
	+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	+ * SUCH DAMAGE.
	+ *
	+ * $FreeBSD$
	+ */
	+
	+#ifndef _AMD64_DETECT_RDFSGSBASE_H_
	+#define _AMD64_DETECT_RDFSGSBASE_H_
	+
	+enum {
	+ RDFSGS_UNKNOWN,
	+ RDFSGS_SUPPORTED,
	+ RDFSGS_UNSUPPORTED,
	+};
	+
	+int amd64_detect_rdfsgsbase(void);
	+
	+#endif
	Index: lib/libc/amd64/sys/amd64_detect_rdfsgsbase.c
	===================================================================
	--- /dev/null
	+++ lib/libc/amd64/sys/amd64_detect_rdfsgsbase.c
	@@ -0,0 +1,63 @@
	+/*-
	+ * Copyright (c) 2017 The FreeBSD Foundation
	+ * All rights reserved.
	+ *
	+ * This software was developed by Konstantin Belousov <kib@FreeBSD.org>
	+ * under sponsorship from the FreeBSD Foundation.
	+ *
	+ * Redistribution and use in source and binary forms, with or without
	+ * modification, are permitted provided that the following conditions
	+ * are met:
	+ * 1. Redistributions of source code must retain the above copyright
	+ * notice, this list of conditions and the following disclaimer.
	+ * 2. Redistributions in binary form must reproduce the above copyright
	+ * notice, this list of conditions and the following disclaimer in the
	+ * documentation and/or other materials provided with the distribution.
	+ *
	+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
	+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	+ * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
	+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	+ * SUCH DAMAGE.
	+ */
	+
	+#include <sys/cdefs.h>
	+__FBSDID("$FreeBSD$");
	+
	+#define IN_RTLD 1
	+#include <sys/param.h>
	+#undef IN_RTLD
	+#include <machine/cpufunc.h>
	+#include <machine/specialreg.h>
	+#include "amd64_detect_rdfsgsbase.h"
	+#include "libc_private.h"
	+
	+static int state = RDFSGS_UNKNOWN;
	+
	+int
	+amd64_detect_rdfsgsbase(void)
	+{
	+ u_int p[4];
	+
	+ if (__predict_true(state != RDFSGS_UNKNOWN))
	+ return (state);
	+
	+ if (__getosreldate() >= P_OSREL_WRFSBASE) {
	+ do_cpuid(0x0, p);
	+ if (p[0] >= 0x7) {
	+ cpuid_count(0x7, 0x0, p);
	+ if ((p[1] & CPUID_STDEXT_FSGSBASE) != 0) {
	+ state = RDFSGS_SUPPORTED;
	+ return (state);
	+ }
	+ }
	+ }
	+ state = RDFSGS_UNSUPPORTED;
	+ return (state);
	+}
	Index: lib/libc/amd64/sys/amd64_get_fsbase.c
	===================================================================
	--- lib/libc/amd64/sys/amd64_get_fsbase.c
	+++ lib/libc/amd64/sys/amd64_get_fsbase.c
	@@ -1,7 +1,11 @@
	/*-
	* Copyright (c) 2003 Peter Wemm
	+ * Copyright (c) 2017 The FreeBSD Foundation
	* All rights reserved.
	*
	+ * Portions of this software were developed by Konstantin Belousov
	+ * under sponsorship from the FreeBSD Foundation.
	+ *
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	@@ -27,11 +31,18 @@
	#include <sys/cdefs.h>
	__FBSDID("$FreeBSD$");

	+#include <sys/types.h>
	+#include <machine/cpufunc.h>
	#include <machine/sysarch.h>
	+#include "amd64_detect_rdfsgsbase.h"

	int
	amd64_get_fsbase(void **addr)
	{

	+ if (amd64_detect_rdfsgsbase() == RDFSGS_SUPPORTED) {
	+ addr = (void )rdfsbase();
	+ return (0);
	+ }
	return (sysarch(AMD64_GET_FSBASE, addr));
	}
	Index: lib/libc/amd64/sys/amd64_get_gsbase.c
	===================================================================
	--- lib/libc/amd64/sys/amd64_get_gsbase.c
	+++ lib/libc/amd64/sys/amd64_get_gsbase.c
	@@ -1,7 +1,11 @@
	/*-
	* Copyright (c) 2003 Peter Wemm
	+ * Copyright (c) 2017 The FreeBSD Foundation
	* All rights reserved.
	*
	+ * Portions of this software were developed by Konstantin Belousov
	+ * under sponsorship from the FreeBSD Foundation.
	+ *
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	@@ -27,11 +31,18 @@
	#include <sys/cdefs.h>
	__FBSDID("$FreeBSD$");

	+#include <sys/types.h>
	+#include <machine/cpufunc.h>
	#include <machine/sysarch.h>
	+#include "amd64_detect_rdfsgsbase.h"

	int
	amd64_get_gsbase(void **addr)
	{

	+ if (amd64_detect_rdfsgsbase() == RDFSGS_SUPPORTED) {
	+ addr = (void )rdgsbase();
	+ return (0);
	+ }
	return (sysarch(AMD64_GET_GSBASE, addr));
	}
	Index: lib/libc/amd64/sys/amd64_set_fsbase.c
	===================================================================
	--- lib/libc/amd64/sys/amd64_set_fsbase.c
	+++ lib/libc/amd64/sys/amd64_set_fsbase.c
	@@ -1,7 +1,11 @@
	/*-
	* Copyright (c) 2003 Peter Wemm
	+ * Copyright (c) 2017 The FreeBSD Foundation
	* All rights reserved.
	*
	+ * Portions of this software were developed by Konstantin Belousov
	+ * under sponsorship from the FreeBSD Foundation.
	+ *
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	@@ -27,11 +31,18 @@
	#include <sys/cdefs.h>
	__FBSDID("$FreeBSD$");

	+#include <sys/types.h>
	+#include <machine/cpufunc.h>
	#include <machine/sysarch.h>
	+#include "amd64_detect_rdfsgsbase.h"

	int
	amd64_set_fsbase(void *addr)
	{

	+ if (amd64_detect_rdfsgsbase() == RDFSGS_SUPPORTED) {
	+ wrfsbase((uintptr_t)addr);
	+ return (0);
	+ }
	return (sysarch(AMD64_SET_FSBASE, &addr));
	}
	Index: lib/libc/amd64/sys/amd64_set_gsbase.c
	===================================================================
	--- lib/libc/amd64/sys/amd64_set_gsbase.c
	+++ lib/libc/amd64/sys/amd64_set_gsbase.c
	@@ -1,7 +1,11 @@
	/*-
	* Copyright (c) 2003 Peter Wemm
	+ * Copyright (c) 2017 The FreeBSD Foundation
	* All rights reserved.
	*
	+ * Portions of this software were developed by Konstantin Belousov
	+ * under sponsorship from the FreeBSD Foundation.
	+ *
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	@@ -27,11 +31,18 @@
	#include <sys/cdefs.h>
	__FBSDID("$FreeBSD$");

	+#include <sys/types.h>
	+#include <machine/cpufunc.h>
	#include <machine/sysarch.h>
	+#include "amd64_detect_rdfsgsbase.h"

	int
	amd64_set_gsbase(void *addr)
	{

	+ if (amd64_detect_rdfsgsbase() == RDFSGS_SUPPORTED) {
	+ wrgsbase((uintptr_t)addr);
	+ return (0);
	+ }
	return (sysarch(AMD64_SET_GSBASE, &addr));
	}
	Index: sys/amd64/amd64/cpu_switch.S
	===================================================================
	--- sys/amd64/amd64/cpu_switch.S
	+++ sys/amd64/amd64/cpu_switch.S
	@@ -87,7 +87,6 @@
	ENTRY(cpu_switch)
	/* Switch to new thread. First, save context. */
	movq TD_PCB(%rdi),%r8
	- orl $PCB_FULL_IRET,PCB_FLAGS(%r8)

	movq (%rsp),%rax /* Hardware registers */
	movq %r15,PCB_R15(%r8)
	@@ -99,6 +98,30 @@
	movq %rbx,PCB_RBX(%r8)
	movq %rax,PCB_RIP(%r8)

	+ testl $PCB_FULL_IRET,PCB_FLAGS(%r8)
	+ jnz 2f
	+ orl $PCB_FULL_IRET,PCB_FLAGS(%r8)
	+ testl $TDP_KTHREAD,TD_PFLAGS(%rdi)
	+ jnz 2f
	+ testb $CPUID_STDEXT_FSGSBASE,cpu_stdext_feature(%rip)
	+ jz 2f
	+ movl %fs,%eax
	+ cmpl $KUF32SEL,%eax
	+ jne 1f
	+ rdfsbaseq %rax
	+ movq %rax,PCB_FSBASE(%r8)
	+1: movl %gs,%eax
	+ cmpl $KUG32SEL,%eax
	+ jne 2f
	+ movq %rdx,%r12
	+ movl $MSR_KGSBASE,%ecx /* Read user gs base */
	+ rdmsr
	+ shlq $32,%rdx
	+ orq %rdx,%rax
	+ movq %rax,PCB_GSBASE(%r8)
	+ movq %r12,%rdx
	+
	+2:
	testl $PCB_DBREGS,PCB_FLAGS(%r8)
	jnz store_dr /* static predict not taken */
	done_store_dr:
	Index: sys/amd64/amd64/exception.S
	===================================================================
	--- sys/amd64/amd64/exception.S
	+++ sys/amd64/amd64/exception.S
	@@ -187,12 +187,13 @@
	jz alltraps_pushregs_no_rdi
	sti
	alltraps_pushregs_no_rdi:
	- movq %rsi,TF_RSI(%rsp)
	movq %rdx,TF_RDX(%rsp)
	+ movq %rax,TF_RAX(%rsp)
	+alltraps_pushregs_no_rax:
	+ movq %rsi,TF_RSI(%rsp)
	movq %rcx,TF_RCX(%rsp)
	movq %r8,TF_R8(%rsp)
	movq %r9,TF_R9(%rsp)
	- movq %rax,TF_RAX(%rsp)
	movq %rbx,TF_RBX(%rsp)
	movq %rbp,TF_RBP(%rsp)
	movq %r10,TF_R10(%rsp)
	@@ -326,22 +327,44 @@
	prot_addrf:
	movq $0,TF_ADDR(%rsp)
	movq %rdi,TF_RDI(%rsp) /* free up a GP register */
	+ movq %rax,TF_RAX(%rsp)
	+ movq %rdx,TF_RDX(%rsp)
	+ movw %fs,TF_FS(%rsp)
	+ movw %gs,TF_GS(%rsp)
	leaq doreti_iret(%rip),%rdi
	cmpq %rdi,TF_RIP(%rsp)
	- je 1f /* kernel but with user gsbase!! */
	+ je 5f /* kernel but with user gsbase!! */
	testb $SEL_RPL_MASK,TF_CS(%rsp) /* Did we come from kernel? */
	- jz 2f /* already running with kernel GS.base */
	-1: swapgs
	-2: movq PCPU(CURPCB),%rdi
	- orl $PCB_FULL_IRET,PCB_FLAGS(%rdi) /* always full iret from GPF */
	- movw %fs,TF_FS(%rsp)
	- movw %gs,TF_GS(%rsp)
	+ jz 6f /* already running with kernel GS.base */
	+ testb $CPUID_STDEXT_FSGSBASE,cpu_stdext_feature(%rip)
	+ jz 2f
	+ cmpw $KUF32SEL,TF_FS(%rsp)
	+ jne 1f
	+ rdfsbaseq %rax
	+1: cmpw $KUG32SEL,TF_GS(%rsp)
	+ jne 2f
	+ rdgsbaseq %rdx
	+2: swapgs
	+ movq PCPU(CURPCB),%rdi
	+ testb $CPUID_STDEXT_FSGSBASE,cpu_stdext_feature(%rip)
	+ jz 4f
	+ cmpw $KUF32SEL,TF_FS(%rsp)
	+ jne 3f
	+ movq %rax,PCB_FSBASE(%rdi)
	+3: cmpw $KUG32SEL,TF_GS(%rsp)
	+ jne 4f
	+ movq %rdx,PCB_GSBASE(%rdi)
	+4: orl $PCB_FULL_IRET,PCB_FLAGS(%rdi) /* always full iret from GPF */
	movw %es,TF_ES(%rsp)
	movw %ds,TF_DS(%rsp)
	testl $PSL_I,TF_RFLAGS(%rsp)
	- jz alltraps_pushregs_no_rdi
	+ jz alltraps_pushregs_no_rax
	sti
	- jmp alltraps_pushregs_no_rdi
	+ jmp alltraps_pushregs_no_rax
	+
	+5: swapgs
	+6: movq PCPU(CURPCB),%rdi
	+ jmp 4b

	/*
	* Fast syscall entry point. We enter here with just our new %cs/%ss set,
	@@ -349,8 +372,8 @@
	* pointer. We have to juggle a few things around to find our stack etc.
	* swapgs gives us access to our PCPU space only.
	*
	- * We do not support invoking this from a custom %cs or %ss (e.g. using
	- * entries from an LDT).
	+ * We do not support invoking this from a custom segment registers,
	+ * esp. %cs, %ss, %fs, %gs, e.g. using entries from an LDT.
	*/
	IDTVEC(fast_syscall)
	swapgs
	@@ -503,6 +526,23 @@
	nmi_fromuserspace:
	incl %ebx
	swapgs
	+ testb $CPUID_STDEXT_FSGSBASE,cpu_stdext_feature(%rip)
	+ jz 2f
	+ movq PCPU(CURPCB),%rdi
	+ testq %rdi,%rdi
	+ jz 2f
	+ cmpw $KUF32SEL,TF_FS(%rsp)
	+ jne 1f
	+ rdfsbaseq %rax
	+ movq %rax,PCB_FSBASE(%rdi)
	+1: cmpw $KUG32SEL,TF_GS(%rsp)
	+ jne 2f
	+ movl $MSR_KGSBASE,%ecx
	+ rdmsr
	+ shlq $32,%rdx
	+ orq %rdx,%rax
	+ movq %rax,PCB_GSBASE(%rdi)
	+2:
	/* Note: this label is also used by ddb and gdb: */
	nmi_calltrap:
	FAKE_MCOUNT(TF_RIP(%rsp))
	@@ -705,6 +745,7 @@
	jz ld_regs
	testl $PCB_FULL_IRET,PCB_FLAGS(%r8)
	jz ld_regs
	+ andl $~PCB_FULL_IRET,PCB_FLAGS(%r8)
	testl $TF_HASSEGS,TF_FLAGS(%rsp)
	je set_segs

	Index: sys/amd64/amd64/machdep.c
	===================================================================
	--- sys/amd64/amd64/machdep.c
	+++ sys/amd64/amd64/machdep.c
	@@ -372,6 +372,7 @@
	sf.sf_uc.uc_mcontext.mc_len = sizeof(sf.sf_uc.uc_mcontext); /* magic */
	get_fpcontext(td, &sf.sf_uc.uc_mcontext, xfpusave, xfpusave_len);
	fpstate_drop(td);
	+ update_pcb_bases(pcb);
	sf.sf_uc.uc_mcontext.mc_fsbase = pcb->pcb_fsbase;
	sf.sf_uc.uc_mcontext.mc_gsbase = pcb->pcb_gsbase;
	bzero(sf.sf_uc.uc_mcontext.mc_spare,
	@@ -442,7 +443,6 @@
	regs->tf_fs = _ufssel;
	regs->tf_gs = _ugssel;
	regs->tf_flags = TF_HASSEGS;
	- set_pcb_flags(pcb, PCB_FULL_IRET);
	PROC_LOCK(p);
	mtx_lock(&psp->ps_mtx);
	}
	@@ -548,6 +548,7 @@
	return (ret);
	}
	bcopy(&ucp->uc_mcontext.mc_rdi, regs, sizeof(*regs));
	+ update_pcb_bases(pcb);
	pcb->pcb_fsbase = ucp->uc_mcontext.mc_fsbase;
	pcb->pcb_gsbase = ucp->uc_mcontext.mc_gsbase;

	@@ -559,7 +560,6 @@
	#endif

	kern_sigprocmask(td, SIG_SETMASK, &ucp->uc_sigmask, NULL, 0);
	- set_pcb_flags(pcb, PCB_FULL_IRET);
	return (EJUSTRETURN);
	}

	@@ -587,11 +587,11 @@
	else
	mtx_unlock(&dt_lock);

	+ update_pcb_bases(pcb);
	pcb->pcb_fsbase = 0;
	pcb->pcb_gsbase = 0;
	clear_pcb_flags(pcb, PCB_32BIT);
	pcb->pcb_initial_fpucw = __INITIAL_FPUCW__;
	- set_pcb_flags(pcb, PCB_FULL_IRET);

	bzero((char *)regs, sizeof(struct trapframe));
	regs->tf_rip = imgp->entry_addr;
	@@ -2135,6 +2135,7 @@
	mcp->mc_flags = tp->tf_flags;
	mcp->mc_len = sizeof(*mcp);
	get_fpcontext(td, mcp, NULL, 0);
	+ update_pcb_bases(pcb);
	mcp->mc_fsbase = pcb->pcb_fsbase;
	mcp->mc_gsbase = pcb->pcb_gsbase;
	mcp->mc_xfpustate = 0;
	@@ -2205,11 +2206,11 @@
	tp->tf_fs = mcp->mc_fs;
	tp->tf_gs = mcp->mc_gs;
	}
	+ set_pcb_flags(pcb, PCB_FULL_IRET);
	if (mcp->mc_flags & _MC_HASBASES) {
	pcb->pcb_fsbase = mcp->mc_fsbase;
	pcb->pcb_gsbase = mcp->mc_gsbase;
	}
	- set_pcb_flags(pcb, PCB_FULL_IRET);
	return (0);
	}

	@@ -2480,6 +2481,71 @@
	return 0;
	}

	+/*
	+ * The pcb_flags is only modified by current thread, or by other threads
	+ * when current thread is stopped. However, current thread may change it
	+ * from the interrupt context in cpu_switch(), or in the trap handler.
	+ * When we read-modify-write pcb_flags from C sources, compiler may generate
	+ * code that is not atomic regarding the interrupt handler. If a trap or
	+ * interrupt happens and any flag is modified from the handler, it can be
	+ * clobbered with the cached value later. Therefore, we implement setting
	+ * and clearing flags with single-instruction functions, which do not race
	+ * with possible modification of the flags from the trap or interrupt context,
	+ * because traps and interrupts are executed only on instruction boundary.
	+ */
	+void
	+set_pcb_flags_raw(struct pcb *pcb, const u_int flags)
	+{
	+
	+ __asm __volatile("orl %1,%0"
	+ : "=m" (pcb->pcb_flags) : "ir" (flags), "m" (pcb->pcb_flags)
	+ : "cc", "memory");
	+
	+}
	+
	+/*
	+ * The support for RDFSBASE, WRFSBASE and similar instructions for %gs
	+ * base requires that kernel saves MSR_FSBASE and MSR_{K,}GSBASE into
	+ * pcb if user space modified the bases. We must save on the context
	+ * switch or if the return to usermode happens through the doreti.
	+ *
	+ * Tracking of both events is performed by the pcb flag PCB_FULL_IRET,
	+ * which have a consequence that the base MSRs must be saved each time
	+ * the PCB_FULL_IRET flag is set. We disable interrupts to sync with
	+ * context switches.
	+ */
	+void
	+set_pcb_flags(struct pcb *pcb, const u_int flags)
	+{
	+ register_t r;
	+
	+ if (curpcb == pcb &&
	+ (flags & PCB_FULL_IRET) != 0 &&
	+ (pcb->pcb_flags & PCB_FULL_IRET) == 0 &&
	+ (cpu_stdext_feature & CPUID_STDEXT_FSGSBASE) != 0) {
	+ r = intr_disable();
	+ if ((pcb->pcb_flags & PCB_FULL_IRET) == 0) {
	+ if (rfs() == _ufssel)
	+ pcb->pcb_fsbase = rdfsbase();
	+ if (rgs() == _ugssel)
	+ pcb->pcb_gsbase = rdmsr(MSR_KGSBASE);
	+ }
	+ set_pcb_flags_raw(pcb, flags);
	+ intr_restore(r);
	+ } else {
	+ set_pcb_flags_raw(pcb, flags);
	+ }
	+}
	+
	+void
	+clear_pcb_flags(struct pcb *pcb, const u_int flags)
	+{
	+
	+ __asm __volatile("andl %1,%0"
	+ : "=m" (pcb->pcb_flags) : "ir" (~flags), "m" (pcb->pcb_flags)
	+ : "cc", "memory");
	+}
	+
	#ifdef KDB

	/*
	Index: sys/amd64/amd64/ptrace_machdep.c
	===================================================================
	--- sys/amd64/amd64/ptrace_machdep.c
	+++ sys/amd64/amd64/ptrace_machdep.c
	@@ -117,15 +117,17 @@
	static void
	cpu_ptrace_setbase(struct thread *td, int req, register_t r)
	{
	+ struct pcb *pcb;

	+ pcb = td->td_pcb;
	+ set_pcb_flags(pcb, PCB_FULL_IRET);
	if (req == PT_SETFSBASE) {
	- td->td_pcb->pcb_fsbase = r;
	+ pcb->pcb_fsbase = r;
	td->td_frame->tf_fs = _ufssel;
	} else {
	- td->td_pcb->pcb_gsbase = r;
	+ pcb->pcb_gsbase = r;
	td->td_frame->tf_gs = _ugssel;
	}
	- set_pcb_flags(td->td_pcb, PCB_FULL_IRET);
	}

	#ifdef COMPAT_FREEBSD32
	@@ -136,6 +138,7 @@
	cpu32_ptrace(struct thread td, int req, void addr, int data)
	{
	struct savefpu *fpstate;
	+ struct pcb *pcb;
	uint32_t r;
	int error;

	@@ -167,8 +170,10 @@
	error = EINVAL;
	break;
	}
	- r = req == PT_GETFSBASE ? td->td_pcb->pcb_fsbase :
	- td->td_pcb->pcb_gsbase;
	+ pcb = td->td_pcb;
	+ if (td == curthread)
	+ update_pcb_bases(pcb);
	+ r = req == PT_GETFSBASE ? pcb->pcb_fsbase : pcb->pcb_gsbase;
	error = copyout(&r, addr, sizeof(r));
	break;

	@@ -197,6 +202,7 @@
	cpu_ptrace(struct thread td, int req, void addr, int data)
	{
	register_t *r, rv;
	+ struct pcb *pcb;
	int error;

	#ifdef COMPAT_FREEBSD32
	@@ -221,8 +227,10 @@

	case PT_GETFSBASE:
	case PT_GETGSBASE:
	- r = req == PT_GETFSBASE ? &td->td_pcb->pcb_fsbase :
	- &td->td_pcb->pcb_gsbase;
	+ pcb = td->td_pcb;
	+ if (td == curthread)
	+ update_pcb_bases(pcb);
	+ r = req == PT_GETFSBASE ? &pcb->pcb_fsbase : &pcb->pcb_gsbase;
	error = copyout(r, addr, sizeof(*r));
	break;

	Index: sys/amd64/amd64/sys_machdep.c
	===================================================================
	--- sys/amd64/amd64/sys_machdep.c
	+++ sys/amd64/amd64/sys_machdep.c
	@@ -254,39 +254,45 @@
	error = amd64_set_ioperm(td, &iargs);
	break;
	case I386_GET_FSBASE:
	+ update_pcb_bases(pcb);
	i386base = pcb->pcb_fsbase;
	error = copyout(&i386base, uap->parms, sizeof(i386base));
	break;
	case I386_SET_FSBASE:
	error = copyin(uap->parms, &i386base, sizeof(i386base));
	if (!error) {
	+ set_pcb_flags(pcb, PCB_FULL_IRET);
	pcb->pcb_fsbase = i386base;
	td->td_frame->tf_fs = _ufssel;
	update_gdt_fsbase(td, i386base);
	}
	break;
	case I386_GET_GSBASE:
	+ update_pcb_bases(pcb);
	i386base = pcb->pcb_gsbase;
	error = copyout(&i386base, uap->parms, sizeof(i386base));
	break;
	case I386_SET_GSBASE:
	error = copyin(uap->parms, &i386base, sizeof(i386base));
	if (!error) {
	+ set_pcb_flags(pcb, PCB_FULL_IRET);
	pcb->pcb_gsbase = i386base;
	td->td_frame->tf_gs = _ugssel;
	update_gdt_gsbase(td, i386base);
	}
	break;
	case AMD64_GET_FSBASE:
	- error = copyout(&pcb->pcb_fsbase, uap->parms, sizeof(pcb->pcb_fsbase));
	+ update_pcb_bases(pcb);
	+ error = copyout(&pcb->pcb_fsbase, uap->parms,
	+ sizeof(pcb->pcb_fsbase));
	break;

	case AMD64_SET_FSBASE:
	error = copyin(uap->parms, &a64base, sizeof(a64base));
	if (!error) {
	if (a64base < VM_MAXUSER_ADDRESS) {
	- pcb->pcb_fsbase = a64base;
	set_pcb_flags(pcb, PCB_FULL_IRET);
	+ pcb->pcb_fsbase = a64base;
	td->td_frame->tf_fs = _ufssel;
	} else
	error = EINVAL;
	@@ -294,15 +300,17 @@
	break;

	case AMD64_GET_GSBASE:
	- error = copyout(&pcb->pcb_gsbase, uap->parms, sizeof(pcb->pcb_gsbase));
	+ update_pcb_bases(pcb);
	+ error = copyout(&pcb->pcb_gsbase, uap->parms,
	+ sizeof(pcb->pcb_gsbase));
	break;

	case AMD64_SET_GSBASE:
	error = copyin(uap->parms, &a64base, sizeof(a64base));
	if (!error) {
	if (a64base < VM_MAXUSER_ADDRESS) {
	- pcb->pcb_gsbase = a64base;
	set_pcb_flags(pcb, PCB_FULL_IRET);
	+ pcb->pcb_gsbase = a64base;
	td->td_frame->tf_gs = _ugssel;
	} else
	error = EINVAL;
	Index: sys/amd64/amd64/vm_machdep.c
	===================================================================
	--- sys/amd64/amd64/vm_machdep.c
	+++ sys/amd64/amd64/vm_machdep.c
	@@ -238,7 +238,7 @@
	pcb2->pcb_tssp = NULL;

	/* New segment registers. */
	- set_pcb_flags(pcb2, PCB_FULL_IRET);
	+ set_pcb_flags_raw(pcb2, PCB_FULL_IRET);

	/* Copy the LDT, if necessary. */
	mdp1 = &td1->td_proc->p_md;
	@@ -439,7 +439,7 @@
	pcb2->pcb_save = get_pcb_user_save_pcb(pcb2);
	bcopy(get_pcb_user_save_td(td0), pcb2->pcb_save,
	cpu_max_ext_state_size);
	- set_pcb_flags(pcb2, PCB_FULL_IRET);
	+ set_pcb_flags_raw(pcb2, PCB_FULL_IRET);

	/*
	* Create a new fresh stack for the new thread.
	Index: sys/amd64/include/asmacros.h
	===================================================================
	--- sys/amd64/include/asmacros.h
	+++ sys/amd64/include/asmacros.h
	@@ -177,7 +177,12 @@
	movw %es,TF_ES(%rsp) ; \
	movw %ds,TF_DS(%rsp) ; \
	movl $TF_HASSEGS,TF_FLAGS(%rsp) ; \
	- cld
	+ cld ; \
	+ testb $SEL_RPL_MASK,TF_CS(%rsp) ; /* come from kernel ? */ \
	+ jz 2f ; /* yes, leave PCB_FULL_IRET alone */ \
	+ movq PCPU(CURPCB),%r8 ; \
	+ andl $~PCB_FULL_IRET,PCB_FLAGS(%r8) ; \
	+2:

	#define POP_FRAME \
	movq TF_RDI(%rsp),%rdi ; \
	Index: sys/amd64/include/pcb.h
	===================================================================
	--- sys/amd64/include/pcb.h
	+++ sys/amd64/include/pcb.h
	@@ -119,40 +119,15 @@
	#ifdef _KERNEL
	struct trapframe;

	-/*
	- * The pcb_flags is only modified by current thread, or by other threads
	- * when current thread is stopped. However, current thread may change it
	- * from the interrupt context in cpu_switch(), or in the trap handler.
	- * When we read-modify-write pcb_flags from C sources, compiler may generate
	- * code that is not atomic regarding the interrupt handler. If a trap or
	- * interrupt happens and any flag is modified from the handler, it can be
	- * clobbered with the cached value later. Therefore, we implement setting
	- * and clearing flags with single-instruction functions, which do not race
	- * with possible modification of the flags from the trap or interrupt context,
	- * because traps and interrupts are executed only on instruction boundary.
	- */
	-static __inline void
	-set_pcb_flags(struct pcb *pcb, const u_int flags)
	-{
	-
	- __asm __volatile("orl %1,%0"
	- : "=m" (pcb->pcb_flags) : "ir" (flags), "m" (pcb->pcb_flags)
	- : "cc");
	-}
	-
	-static __inline void
	-clear_pcb_flags(struct pcb *pcb, const u_int flags)
	-{
	-
	- __asm __volatile("andl %1,%0"
	- : "=m" (pcb->pcb_flags) : "ir" (~flags), "m" (pcb->pcb_flags)
	- : "cc");
	-}
	-
	+void clear_pcb_flags(struct pcb *pcb, const u_int flags);
	void makectx(struct trapframe , struct pcb );
	+void set_pcb_flags(struct pcb *pcb, const u_int flags);
	+void set_pcb_flags_raw(struct pcb *pcb, const u_int flags);
	int savectx(struct pcb *) __returns_twice;
	void resumectx(struct pcb *);

	+/* Ensure that pcb_gsbase and pcb_fsbase are up to date */
	+#define update_pcb_bases(pcb) set_pcb_flags((pcb), PCB_FULL_IRET)
	#endif

	#endif /* _AMD64_PCB_H_ */
	Index: sys/sys/param.h
	===================================================================
	--- sys/sys/param.h
	+++ sys/sys/param.h
	@@ -58,7 +58,7 @@
	* in the range 5 to 9.
	*/
	#undef __FreeBSD_version
	-#define __FreeBSD_version 1200040 /* Master, propagated to newvers */
	+#define __FreeBSD_version 1200041 /* Master, propagated to newvers */

	/*
	* __FreeBSD_kernel__ indicates that this system uses the kernel of FreeBSD,
	@@ -83,6 +83,7 @@
	#define P_OSREL_MAP_FSTRICT 1100036
	#define P_OSREL_SHUTDOWN_ENOTCONN 1100077
	#define P_OSREL_MAP_GUARD 1200035
	+#define P_OSREL_WRFSBASE 1200041

	#define P_OSREL_MAJOR(x) ((x) / 100000)
	#endif

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