[PATCH v5 07/13] x86/um: nommu: process/thread handling

[Hajime Tazaki]

Since ptrace facility isn't used under !MMU of UML, there is different
code path to invoke processes/threads; there are no external process
used, and need to properly configure some of registers (fs segment
register for TLS, etc) on every context switch, etc.

Signals aren't delivered in non-ptrace syscall entry/leave so, we also
need to handle pending signal by ourselves.

Signed-off-by: Hajime Tazaki <thehajime at gmail.com>
Signed-off-by: Ricardo Koller <ricarkol at google.com>
---
 arch/um/os-Linux/process.c      |  6 +++++
 arch/x86/um/Makefile            |  3 ++-
 arch/x86/um/nommu/Makefile      |  2 +-
 arch/x86/um/nommu/entry_64.S    | 22 +++++++++++++++++
 arch/x86/um/nommu/syscalls_64.c | 44 +++++++++++++++++++++++++++++++++
 5 files changed, 75 insertions(+), 2 deletions(-)
 create mode 100644 arch/x86/um/nommu/syscalls_64.c

diff --git a/arch/um/os-Linux/process.c b/arch/um/os-Linux/process.c
index e2dc00fc84c0..49aa8e92205e 100644
--- a/arch/um/os-Linux/process.c
+++ b/arch/um/os-Linux/process.c
@@ -28,6 +28,9 @@ int unscheduled_userspace_iterations;
 
 void os_alarm_process(int pid)
 {
+	if (pid <= 0)
+		return;
+
 	kill(pid, SIGALRM);
 }
 
@@ -45,6 +48,9 @@ void os_kill_process(int pid, int reap_child)
 
 void os_kill_ptraced_process(int pid, int reap_child)
 {
+	if (pid <= 0)
+		return;
+
 	kill(pid, SIGKILL);
 	ptrace(PTRACE_KILL, pid);
 	ptrace(PTRACE_CONT, pid);
diff --git a/arch/x86/um/Makefile b/arch/x86/um/Makefile
index 227af2a987e2..53c9ebb3c41c 100644
--- a/arch/x86/um/Makefile
+++ b/arch/x86/um/Makefile
@@ -27,7 +27,8 @@ subarch-y += ../kernel/sys_ia32.o
 
 else
 
-obj-y += syscalls_64.o vdso/
+obj-y += vdso/
+obj-$(CONFIG_MMU) += syscalls_64.o
 
 subarch-y = ../lib/csum-partial_64.o ../lib/memcpy_64.o \
 	../lib/memmove_64.o ../lib/memset_64.o
diff --git a/arch/x86/um/nommu/Makefile b/arch/x86/um/nommu/Makefile
index ebe47d4836f4..4018d9e0aba0 100644
--- a/arch/x86/um/nommu/Makefile
+++ b/arch/x86/um/nommu/Makefile
@@ -5,4 +5,4 @@ else
 	BITS := 64
 endif
 
-obj-y = do_syscall_$(BITS).o entry_$(BITS).o os-Linux/
+obj-y = do_syscall_$(BITS).o entry_$(BITS).o syscalls_$(BITS).o os-Linux/
diff --git a/arch/x86/um/nommu/entry_64.S b/arch/x86/um/nommu/entry_64.S
index e9bfc7b93c84..950447dfa66b 100644
--- a/arch/x86/um/nommu/entry_64.S
+++ b/arch/x86/um/nommu/entry_64.S
@@ -89,3 +89,25 @@ ENTRY(__kernel_vsyscall)
 	jmp	*%rcx
 
 END(__kernel_vsyscall)
+
+// void userspace(struct uml_pt_regs *regs)
+ENTRY(userspace)
+
+	/* align the stack for x86_64 ABI */
+	and     $-0x10, %rsp
+	/* Handle any immediate reschedules or signals */
+	call	interrupt_end
+
+	movq	current_ptregs, %rsp
+
+	POP_REGS
+
+	addq	$8, %rsp	/* skip orig_ax */
+	popq	%r11		/* pt_regs->ip */
+	addq	$8, %rsp	/* skip cs */
+	addq	$8, %rsp	/* skip flags */
+	popq	%rsp
+
+	jmp	*%r11
+
+END(userspace)
diff --git a/arch/x86/um/nommu/syscalls_64.c b/arch/x86/um/nommu/syscalls_64.c
new file mode 100644
index 000000000000..c78c442aed1d
--- /dev/null
+++ b/arch/x86/um/nommu/syscalls_64.c
@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2003 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ * Copyright 2003 PathScale, Inc.
+ *
+ * Licensed under the GPL
+ */
+
+#include <linux/sched.h>
+#include <linux/sched/mm.h>
+#include <linux/syscalls.h>
+#include <linux/uaccess.h>
+#include <asm/prctl.h> /* XXX This should get the constants from libc */
+#include <registers.h>
+#include <os.h>
+#include "syscalls.h"
+
+void arch_switch_to(struct task_struct *to)
+{
+	/*
+	 * In !CONFIG_MMU, it doesn't ptrace thus,
+	 * The FS_BASE/GS_BASE registers are saved here.
+	 */
+	current_top_of_stack = task_top_of_stack(to);
+	current_ptregs = (long)task_pt_regs(to);
+
+	if ((to->thread.regs.regs.gp[FS_BASE / sizeof(unsigned long)] == 0) ||
+	    (to->mm == NULL))
+		return;
+
+	/* this changes the FS on every context switch */
+	arch_prctl(to, ARCH_SET_FS,
+		   (void __user *) to->thread.regs.regs.gp[FS_BASE / sizeof(unsigned long)]);
+}
+
+SYSCALL_DEFINE6(mmap, unsigned long, addr, unsigned long, len,
+		unsigned long, prot, unsigned long, flags,
+		unsigned long, fd, unsigned long, off)
+{
+	if (off & ~PAGE_MASK)
+		return -EINVAL;
+
+	return ksys_mmap_pgoff(addr, len, prot, flags, fd, off >> PAGE_SHIFT);
+}
-- 
2.43.0