um: remove copy_context_skas0

The kernel flushes the memory ranges anyway for CoW and does not assume
that the userspace process has anything set up already. So, start with a
fresh process for the new mm context.

Signed-off-by: Benjamin Berg <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Johannes Berg <[email protected]>

Author: benzea

arch/um/include/shared/os.h

@@ -285,7 +285,6 @@ void protect(struct mm_id *mm_idp, unsigned long addr,
 /* skas/process.c */
 extern int is_skas_winch(int pid, int fd, void *data);
 extern int start_userspace(unsigned long stub_stack);
-extern int copy_context_skas0(unsigned long stack, int pid);
 extern void userspace(struct uml_pt_regs *regs, unsigned long *aux_fp_regs);
 extern void new_thread(void *stack, jmp_buf *buf, void (*handler)(void));
 extern void switch_threads(jmp_buf *me, jmp_buf *you);

arch/um/include/shared/skas/stub-data.h

@@ -36,7 +36,6 @@ struct stub_syscall {
 
 struct stub_data {
 	unsigned long offset;
-	int fd;
 	long err, child_err;
 
 	int syscall_data_len;

arch/um/kernel/skas/Makefile

@@ -3,16 +3,14 @@
 # Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
 #
 
-obj-y := clone.o stub.o mmu.o process.o syscall.o uaccess.o
+obj-y := stub.o mmu.o process.o syscall.o uaccess.o
 
-# clone.o and stub.o are in the stub, so it can't be built with profiling
+# stub.o is in the stub, so it can't be built with profiling
 # GCC hardened also auto-enables -fpic, but we need %ebx so it can't work ->
 # disable it
 
-CFLAGS_clone.o := $(CFLAGS_NO_HARDENING)
 CFLAGS_stub.o := $(CFLAGS_NO_HARDENING)
-UNPROFILE_OBJS := clone.o stub.o
-
+UNPROFILE_OBJS := stub.o
 KCOV_INSTRUMENT := n
 
 include $(srctree)/arch/um/scripts/Makefile.rules

arch/um/kernel/skas/clone.c

@@ -21,36 +21,30 @@ static_assert(sizeof(struct stub_data) == STUB_DATA_PAGES * UM_KERN_PAGE_SIZE);
 
 int init_new_context(struct task_struct *task, struct mm_struct *mm)
 {
- 	struct mm_context *from_mm = NULL;
-	struct mm_context *to_mm = &mm->context;
+	struct mm_id *new_id = &mm->context.id;
 	unsigned long stack = 0;
 	int ret = -ENOMEM;
 
 	stack = __get_free_pages(GFP_KERNEL | __GFP_ZERO, ilog2(STUB_DATA_PAGES));
 	if (stack == 0)
 		goto out;
 
-	to_mm->id.stack = stack;
-	if (current->mm != NULL && current->mm != &init_mm)
-		from_mm = &current->mm->context;
+	new_id->stack = stack;
 
 	block_signals_trace();
-	if (from_mm)
-		to_mm->id.u.pid = copy_context_skas0(stack,
-						     from_mm->id.u.pid);
-	else to_mm->id.u.pid = start_userspace(stack);
+	new_id->u.pid = start_userspace(stack);
 	unblock_signals_trace();
 
-	if (to_mm->id.u.pid < 0) {
-		ret = to_mm->id.u.pid;
+	if (new_id->u.pid < 0) {
+		ret = new_id->u.pid;
 		goto out_free;
 	}
 
 	return 0;
 
  out_free:
-	if (to_mm->id.stack != 0)
-		free_pages(to_mm->id.stack, ilog2(STUB_DATA_PAGES));
+	if (new_id->stack != 0)
+		free_pages(new_id->stack, ilog2(STUB_DATA_PAGES));
  out:
 	return ret;
 }

arch/um/kernel/skas/mmu.c

@@ -464,114 +464,6 @@ void userspace(struct uml_pt_regs *regs, unsigned long *aux_fp_regs)
 	}
 }
 
-static unsigned long thread_regs[MAX_REG_NR];
-static unsigned long thread_fp_regs[FP_SIZE];
-
-static int __init init_thread_regs(void)
-{
-	get_safe_registers(thread_regs, thread_fp_regs);
-	/* Set parent's instruction pointer to start of clone-stub */
-	thread_regs[REGS_IP_INDEX] = STUB_CODE +
-				(unsigned long) stub_clone_handler -
-				(unsigned long) __syscall_stub_start;
-
-	/* syscall data as a temporary stack area (top half). */
-	thread_regs[REGS_SP_INDEX] = STUB_DATA +
-				     offsetof(struct stub_data, syscall_data) +
-				     sizeof(((struct stub_data *) 0)->syscall_data) -
-				     sizeof(void *);
-	return 0;
-}
-
-__initcall(init_thread_regs);
-
-int copy_context_skas0(unsigned long new_stack, int pid)
-{
-	int err;
-	unsigned long current_stack = current_stub_stack();
-	struct stub_data *data = (struct stub_data *) current_stack;
-	struct stub_data *child_data = (struct stub_data *) new_stack;
-	unsigned long long new_offset;
-	int new_fd = phys_mapping(uml_to_phys((void *)new_stack), &new_offset);
-
-	/*
-	 * prepare offset and fd of child's stack as argument for parent's
-	 * and child's mmap2 calls
-	 */
-	*data = ((struct stub_data) {
-		.offset	= MMAP_OFFSET(new_offset),
-		.fd     = new_fd,
-		.err    = -ESRCH,
-		.child_err = 0,
-	});
-
-	*child_data = ((struct stub_data) {
-		.child_err = -ESRCH,
-	});
-
-	err = ptrace_setregs(pid, thread_regs);
-	if (err < 0) {
-		err = -errno;
-		printk(UM_KERN_ERR "%s : PTRACE_SETREGS failed, pid = %d, errno = %d\n",
-		      __func__, pid, -err);
-		return err;
-	}
-
-	err = put_fp_registers(pid, thread_fp_regs);
-	if (err < 0) {
-		printk(UM_KERN_ERR "%s : put_fp_registers failed, pid = %d, err = %d\n",
-		       __func__, pid, err);
-		return err;
-	}
-
-	/*
-	 * Wait, until parent has finished its work: read child's pid from
-	 * parent's stack, and check, if bad result.
-	 */
-	err = ptrace(PTRACE_CONT, pid, 0, 0);
-	if (err) {
-		err = -errno;
-		printk(UM_KERN_ERR "Failed to continue new process, pid = %d, errno = %d\n",
-		       pid, errno);
-		return err;
-	}
-
-	wait_stub_done(pid);
-
-	pid = data->err;
-	if (pid < 0) {
-		printk(UM_KERN_ERR "%s - stub-parent reports error %d\n",
-		      __func__, -pid);
-		return pid;
-	}
-
-	/*
-	 * Wait, until child has finished too: read child's result from
-	 * child's stack and check it.
-	 */
-	wait_stub_done(pid);
-	if (child_data->child_err != STUB_DATA) {
-		printk(UM_KERN_ERR "%s - stub-child %d reports error %ld\n",
-		       __func__, pid, data->child_err);
-		err = data->child_err;
-		goto out_kill;
-	}
-
-	if (ptrace(PTRACE_SETOPTIONS, pid, NULL,
-		   (void *)PTRACE_O_TRACESYSGOOD) < 0) {
-		err = -errno;
-		printk(UM_KERN_ERR "%s : PTRACE_SETOPTIONS failed, errno = %d\n",
-		       __func__, errno);
-		goto out_kill;
-	}
-
-	return pid;
-
- out_kill:
-	os_kill_ptraced_process(pid, 1);
-	return err;
-}
-
 void new_thread(void *stack, jmp_buf *buf, void (*handler)(void))
 {
 	(*buf)[0].JB_IP = (unsigned long) handler;

arch/um/os-Linux/skas/process.c

@@ -13,4 +13,3 @@
 
 extern void stub_segv_handler(int, siginfo_t *, void *);
 extern void stub_syscall_handler(void);
-extern void stub_clone_handler(void);

arch/x86/um/shared/sysdep/stub.h

@@ -107,30 +107,6 @@ static __always_inline void trap_myself(void)
 	__asm("int3");
 }
 
-static __always_inline void remap_stack_and_trap(void)
-{
-	__asm__ volatile (
-		"movl %%esp,%%ebx ;"
-		"andl %0,%%ebx ;"
-		"movl %1,%%eax ;"
-		"movl %%ebx,%%edi ; addl %2,%%edi ; movl (%%edi),%%edi ;"
-		"movl %%ebx,%%ebp ; addl %3,%%ebp ; movl (%%ebp),%%ebp ;"
-		"int $0x80 ;"
-		"addl %4,%%ebx ; movl %%eax, (%%ebx) ;"
-		"int $3"
-		: :
-		"g" (~(STUB_DATA_PAGES * UM_KERN_PAGE_SIZE - 1)),
-		"g" (STUB_MMAP_NR),
-		"g" (offsetof(struct stub_data, fd)),
-		"g" (offsetof(struct stub_data, offset)),
-		"g" (offsetof(struct stub_data, child_err)),
-		"c" (STUB_DATA_PAGES * UM_KERN_PAGE_SIZE),
-		"d" (PROT_READ | PROT_WRITE),
-		"S" (MAP_FIXED | MAP_SHARED)
-		:
-		"memory");
-}
-
 static __always_inline void *get_stub_data(void)
 {
 	unsigned long ret;

arch/x86/um/shared/sysdep/stub_32.h

@@ -101,32 +101,6 @@ static __always_inline void trap_myself(void)
 	__asm("int3");
 }
 
-static __always_inline void remap_stack_and_trap(void)
-{
-	__asm__ volatile (
-		"movq %0,%%rax ;"
-		"movq %%rsp,%%rdi ;"
-		"andq %1,%%rdi ;"
-		"movq %2,%%r10 ;"
-		"movq %%rdi,%%r8 ; addq %3,%%r8 ; movq (%%r8),%%r8 ;"
-		"movq %%rdi,%%r9 ; addq %4,%%r9 ; movq (%%r9),%%r9 ;"
-		__syscall ";"
-		"movq %%rsp,%%rdi ; andq %1,%%rdi ;"
-		"addq %5,%%rdi ; movq %%rax, (%%rdi) ;"
-		"int3"
-		: :
-		"g" (STUB_MMAP_NR),
-		"g" (~(STUB_DATA_PAGES * UM_KERN_PAGE_SIZE - 1)),
-		"g" (MAP_FIXED | MAP_SHARED),
-		"g" (offsetof(struct stub_data, fd)),
-		"g" (offsetof(struct stub_data, offset)),
-		"g" (offsetof(struct stub_data, child_err)),
-		"S" (STUB_DATA_PAGES * UM_KERN_PAGE_SIZE),
-		"d" (PROT_READ | PROT_WRITE)
-		:
-		__syscall_clobber, "r10", "r8", "r9");
-}
-
 static __always_inline void *get_stub_data(void)
 {
 	unsigned long ret;