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Date: Wed, 4 Feb 2009 09:02:57 +0100
From: Renzo Davoli <renzo@...unibo.it>
To: LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH 2/2] ptrace_vm: ptrace for syscall emulation virtual
machines
This patch adds the new PTRACE_VM_SKIPCALL and PTRACE_VM_SKIPEXIT
tags for ptrace's addr parameter.
In this way it is possible to (eventually) get rid of PTRACE_SYSEMU
PTRACE_SYSEMU_SINGLESTEP, while providing not only the same features
but a more general support for Virtual Machines.
Part#2: user-mode Linux support.
User-mode Linux by this patch uses PTRACE_VM of the hosting operating system
and provides PTRACE_VM to its processes.
UML tests at startup which features are provided and uses PTRACE_VM or
PTRACE_SYSEMU (or nothing). PTRACE_VM and/or PTRACE_SYSEMU support can be
disabled by command line flags.
It is possible to test this patch by running a UML inside a UML (note that with
vanilla kernel UML on UML is currently broken without the patchfix I
published a few days ago. If you apply just the patch of this message UML on
UML works provided that the outer UML provides PTRACE_VM and the support
for PTRACE_VM in the inner UML is not disabled, otherwise my previous patch
is needed. Shortcut: apply my previous patch before this in any case)
renzo
Signed-off-by: Renzo Davoli <renzo@...unibo.it>
---
diff -Naur linux-2.6.28.2/arch/um/include/shared/kern_util.h linux-2.6.28.2-vm/arch/um/include/shared/kern_util.h
--- linux-2.6.28.2/arch/um/include/shared/kern_util.h 2009-01-25 01:42:07.000000000 +0100
+++ linux-2.6.28.2-vm/arch/um/include/shared/kern_util.h 2009-02-02 14:31:32.000000000 +0100
@@ -57,7 +57,7 @@
extern unsigned long to_irq_stack(unsigned long *mask_out);
extern unsigned long from_irq_stack(int nested);
-extern void syscall_trace(struct uml_pt_regs *regs, int entryexit);
+extern int syscall_trace(struct uml_pt_regs *regs, int entryexit);
extern int singlestepping(void *t);
extern void segv_handler(int sig, struct uml_pt_regs *regs);
diff -Naur linux-2.6.28.2/arch/um/include/shared/ptrace_user.h linux-2.6.28.2-vm/arch/um/include/shared/ptrace_user.h
--- linux-2.6.28.2/arch/um/include/shared/ptrace_user.h 2009-01-25 01:42:07.000000000 +0100
+++ linux-2.6.28.2-vm/arch/um/include/shared/ptrace_user.h 2009-02-02 14:31:32.000000000 +0100
@@ -40,9 +40,20 @@
#define PTRACE_OLDSETOPTIONS PTRACE_SETOPTIONS
#endif
+/* these constant should eventually enter in sys/ptrace.h */
+#ifndef PTRACE_SYSCALL_SKIPCALL
+#define PTRACE_SYSCALL_SKIPCALL 0x6
+#endif
+#ifndef PTRACE_SYSCALL_SKIPEXIT
+#define PTRACE_SYSCALL_SKIPEXIT 0x2
+#endif
+
void set_using_sysemu(int value);
int get_using_sysemu(void);
extern int sysemu_supported;
+void set_using_sysptvm(int value);
+int get_using_sysptvm(void);
+extern int sysptvm_supported;
#define SELECT_PTRACE_OPERATION(sysemu_mode, singlestep_mode) \
(((int[3][3] ) { \
diff -Naur linux-2.6.28.2/arch/um/kernel/process.c linux-2.6.28.2-vm/arch/um/kernel/process.c
--- linux-2.6.28.2/arch/um/kernel/process.c 2009-01-25 01:42:07.000000000 +0100
+++ linux-2.6.28.2-vm/arch/um/kernel/process.c 2009-02-02 14:31:32.000000000 +0100
@@ -322,7 +322,9 @@
}
static atomic_t using_sysemu = ATOMIC_INIT(0);
+static atomic_t using_sysptvm = ATOMIC_INIT(0);
int sysemu_supported;
+int sysptvm_supported;
void set_using_sysemu(int value)
{
@@ -336,6 +338,16 @@
return atomic_read(&using_sysemu);
}
+void set_using_sysptvm(int value)
+{
+ atomic_set(&using_sysptvm, value);
+}
+
+int get_using_sysptvm(void)
+{
+ return atomic_read(&using_sysptvm);
+}
+
static int proc_read_sysemu(char *buf, char **start, off_t offset, int size,int *eof, void *data)
{
if (snprintf(buf, size, "%d\n", get_using_sysemu()) < size)
@@ -358,27 +370,63 @@
return count;
}
-int __init make_proc_sysemu(void)
+
+static int proc_read_sysptvm(char *buf, char **start, off_t offset, int size,int *eof, void *data)
{
- struct proc_dir_entry *ent;
- if (!sysemu_supported)
- return 0;
+ int sysptvm=(get_using_sysptvm() != 0);
+ if (snprintf(buf, size, "%d\n", sysptvm) < size)
+ /* No overflow */
+ *eof = 1;
- ent = create_proc_entry("sysemu", 0600, NULL);
+ return strlen(buf);
+}
- if (ent == NULL)
- {
- printk(KERN_WARNING "Failed to register /proc/sysemu\n");
- return 0;
- }
+static int proc_write_sysptvm(struct file *file,const char __user *buf, unsigned long count,void *data)
+{
+ char tmp[2];
+
+ if (copy_from_user(tmp, buf, 1))
+ return -EFAULT;
+
+ if (tmp[0] == '0')
+ set_using_sysptvm(0);
+ if (tmp[0] == '1')
+ set_using_sysemu(/* XXX */ 6);
+ /* We use the first char, but pretend to write everything */
+ return count;
+}
- ent->read_proc = proc_read_sysemu;
- ent->write_proc = proc_write_sysemu;
+int __init make_proc_sysemu_or_sysptvm(void)
+{
+ struct proc_dir_entry *ent;
+ if (sysptvm_supported) {
+ ent = create_proc_entry("sysptvm", 0600, NULL);
+
+ if (ent == NULL)
+ {
+ printk(KERN_WARNING "Failed to register /proc/sysptvm\n");
+ return 0;
+ }
+
+ ent->read_proc = proc_read_sysptvm;
+ ent->write_proc = proc_write_sysptvm;
+ } else if (sysemu_supported) {
+ ent = create_proc_entry("sysemu", 0600, NULL);
+
+ if (ent == NULL)
+ {
+ printk(KERN_WARNING "Failed to register /proc/sysemu\n");
+ return 0;
+ }
+
+ ent->read_proc = proc_read_sysemu;
+ ent->write_proc = proc_write_sysemu;
+ }
return 0;
}
-late_initcall(make_proc_sysemu);
+late_initcall(make_proc_sysemu_or_sysptvm);
int singlestepping(void * t)
{
diff -Naur linux-2.6.28.2/arch/um/kernel/ptrace.c linux-2.6.28.2-vm/arch/um/kernel/ptrace.c
--- linux-2.6.28.2/arch/um/kernel/ptrace.c 2009-01-25 01:42:07.000000000 +0100
+++ linux-2.6.28.2-vm/arch/um/kernel/ptrace.c 2009-02-02 14:31:32.000000000 +0100
@@ -64,6 +64,11 @@
ret = poke_user(child, addr, data);
break;
+ case PTRACE_SYSEMU:
+ case PTRACE_SYSEMU_SINGLESTEP:
+ ret=-EIO;
+ break;
+
/* continue and stop at next (return from) syscall */
case PTRACE_SYSCALL:
/* restart after signal. */
@@ -76,6 +81,8 @@
if (request == PTRACE_SYSCALL)
set_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
else clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
+ child->ptrace &= ~PT_SYSCALL_MASK;
+ child->ptrace |= (addr & PTRACE_SYSCALL_MASK) << 28;
child->exit_code = data;
wake_up_process(child);
ret = 0;
@@ -102,7 +109,9 @@
ret = -EIO;
if (!valid_signal(data))
break;
+ child->ptrace &= ~PT_SYSCALL_MASK;
clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
+ child->ptrace |= (addr & PTRACE_SYSCALL_MASK) << 28;
set_singlestepping(child, 1);
child->exit_code = data;
/* give it a chance to run. */
@@ -245,7 +254,7 @@
* XXX Check PT_DTRACE vs TIF_SINGLESTEP for singlestepping check and
* PT_PTRACED vs TIF_SYSCALL_TRACE for syscall tracing check
*/
-void syscall_trace(struct uml_pt_regs *regs, int entryexit)
+int syscall_trace(struct uml_pt_regs *regs, int entryexit)
{
int is_singlestep = (current->ptrace & PT_DTRACE) && entryexit;
int tracesysgood;
@@ -267,10 +276,13 @@
send_sigtrap(current, regs, 0);
if (!test_thread_flag(TIF_SYSCALL_TRACE))
- return;
+ return 0;
if (!(current->ptrace & PT_PTRACED))
- return;
+ return 0;
+
+ if (entryexit && (current->ptrace & PT_SYSCALL_SKIPEXIT))
+ return 0;
/*
* the 0x80 provides a way for the tracing parent to distinguish
@@ -291,4 +303,8 @@
send_sig(current->exit_code, current, 1);
current->exit_code = 0;
}
+ if (!entryexit && (current->ptrace & PT_SYSCALL_SKIPCALL))
+ return 1;
+ else
+ return 0;
}
diff -Naur linux-2.6.28.2/arch/um/kernel/skas/syscall.c linux-2.6.28.2-vm/arch/um/kernel/skas/syscall.c
--- linux-2.6.28.2/arch/um/kernel/skas/syscall.c 2009-01-25 01:42:07.000000000 +0100
+++ linux-2.6.28.2-vm/arch/um/kernel/skas/syscall.c 2009-02-02 14:31:32.000000000 +0100
@@ -17,8 +17,9 @@
struct pt_regs *regs = container_of(r, struct pt_regs, regs);
long result;
int syscall;
+ int skip_call;
- syscall_trace(r, 0);
+ skip_call=syscall_trace(r, 0);
/*
* This should go in the declaration of syscall, but when I do that,
@@ -29,12 +30,14 @@
* gcc version 4.0.1 20050727 (Red Hat 4.0.1-5)
* in case it's a compiler bug.
*/
- syscall = UPT_SYSCALL_NR(r);
- if ((syscall >= NR_syscalls) || (syscall < 0))
- result = -ENOSYS;
- else result = EXECUTE_SYSCALL(syscall, regs);
+ if (skip_call == 0) {
+ syscall = UPT_SYSCALL_NR(r);
+ if ((syscall >= NR_syscalls) || (syscall < 0))
+ result = -ENOSYS;
+ else result = EXECUTE_SYSCALL(syscall, regs);
- REGS_SET_SYSCALL_RETURN(r->gp, result);
+ REGS_SET_SYSCALL_RETURN(r->gp, result);
+ }
syscall_trace(r, 1);
}
diff -Naur linux-2.6.28.2/arch/um/os-Linux/skas/process.c linux-2.6.28.2-vm/arch/um/os-Linux/skas/process.c
--- linux-2.6.28.2/arch/um/os-Linux/skas/process.c 2009-01-25 01:42:07.000000000 +0100
+++ linux-2.6.28.2-vm/arch/um/os-Linux/skas/process.c 2009-02-02 14:31:32.000000000 +0100
@@ -157,7 +157,7 @@
* (in local_using_sysemu
*/
static void handle_trap(int pid, struct uml_pt_regs *regs,
- int local_using_sysemu)
+ int local_using_sysptvm_or_sysemu)
{
int err, status;
@@ -167,7 +167,7 @@
/* Mark this as a syscall */
UPT_SYSCALL_NR(regs) = PT_SYSCALL_NR(regs->gp);
- if (!local_using_sysemu)
+ if (!local_using_sysptvm_or_sysemu)
{
err = ptrace(PTRACE_POKEUSR, pid, PT_SYSCALL_NR_OFFSET,
__NR_getpid);
@@ -354,6 +354,7 @@
int err, status, op, pid = userspace_pid[0];
/* To prevent races if using_sysemu changes under us.*/
int local_using_sysemu;
+ int local_using_sysptvm;
if (getitimer(ITIMER_VIRTUAL, &timer))
printk(UM_KERN_ERR "Failed to get itimer, errno = %d\n", errno);
@@ -375,11 +376,12 @@
/* Now we set local_using_sysemu to be used for one loop */
local_using_sysemu = get_using_sysemu();
+ local_using_sysptvm = get_using_sysptvm();
op = SELECT_PTRACE_OPERATION(local_using_sysemu,
singlestepping(NULL));
- if (ptrace(op, pid, 0, 0)) {
+ if (ptrace(op, pid, local_using_sysptvm, 0)) {
printk(UM_KERN_ERR "userspace - ptrace continue "
"failed, op = %d, errno = %d\n", op, errno);
fatal_sigsegv();
diff -Naur linux-2.6.28.2/arch/um/os-Linux/start_up.c linux-2.6.28.2-vm/arch/um/os-Linux/start_up.c
--- linux-2.6.28.2/arch/um/os-Linux/start_up.c 2009-01-25 01:42:07.000000000 +0100
+++ linux-2.6.28.2-vm/arch/um/os-Linux/start_up.c 2009-02-02 14:31:32.000000000 +0100
@@ -198,6 +198,35 @@
" See http://perso.wanadoo.fr/laurent.vivier/UML/ for further \n"
" information.\n\n");
+/* Changed only during early boot */
+static int force_sysptvm_disabled = 0;
+
+static int __init nosysptvm_cmd_param(char *str, int* add)
+{
+ force_sysptvm_disabled = 1;
+ return 0;
+}
+
+__uml_setup("nosysptvm", nosysptvm_cmd_param,
+ "nosysptvm\n"
+ " Turns off syscall emulation tags for ptrace (ptrace_vm) on.\n"
+ " Ptrace_vm is a feature introduced by Renzo Davoli. It changes\n"
+ " behaviour of ptrace() and helps reducing host context switch rate.\n"
+ "\n");
+
+static int use_sysemu = 0;
+
+static int __init usesysemu_cmd_param(char *str, int* add)
+{
+ use_sysemu = 1;
+ return 0;
+}
+
+__uml_setup("usesysemu", usesysemu_cmd_param,
+ "usesysemu\n"
+ " Use sysemu instead of sysptvm even when the kernel supports it.\n\n"
+ );
+
static void __init check_sysemu(void)
{
unsigned long regs[MAX_REG_NR];
@@ -293,6 +322,102 @@
non_fatal("missing\n");
}
+/* test thread code. This thread is started only to test
+ * which features are provided by the linux kernel */
+static int sysptvm_child(void *arg)
+{
+ int *featurep=arg;
+ int p[2]={-1,-1};
+ pid_t pid=os_getpid();
+ if(ptrace(PTRACE_TRACEME, 0, 0, 0) < 0){
+ perror("ptrace test_ptracemulti");
+ kill(pid, SIGKILL);
+ }
+ kill(pid, SIGSTOP);
+ *featurep=0;
+ os_getpid();
+ /* if it reaches this point in 1 stop it means that
+ * PTRACE_SYSCALL_SKIPEXIT works */
+ *featurep=PTRACE_SYSCALL_SKIPEXIT;
+ pipe(p);
+ /* if after a PTRACE_SYSCALL_SKIPCALL p[0] is already <0
+ * pipe has been really skipped */
+ if (p[0] < 0)
+ *featurep=PTRACE_SYSCALL_SKIPCALL;
+ else { /* clean up everything */
+ close(p[0]);
+ close(p[1]);
+ }
+ return 0;
+}
+
+/* kernel feature test:
+ * it returns:
+ * -1 error
+ * 0 old PTRACE_SYSCALL (addr is ignored)
+ * PTRACE_SYSCALL_SKIPEXIT: just skip_exit is provided
+ * PTRACE_SYSCALL_SKIPCALL: the entire syntax is implemented
+ * by the running kernel */
+static int __init test_ptrace_sysptvm(void) {
+ int pid, status, rv, feature;
+ static char stack[1024];
+ feature=0;
+
+ if((pid = clone(sysptvm_child, &stack[1020], SIGCHLD | CLONE_VM, &feature)) < 0)
+ return 0;
+ if(waitpid(pid, &status, WUNTRACED) < 0){
+ kill(pid, SIGKILL);
+ return 0;
+ }
+ /* restart and wait for the next syscall (getpid)*/
+ rv=ptrace(PTRACE_SYSCALL, pid, 0, 0);
+ if(waitpid(pid, &status, WUNTRACED) < 0)
+ goto out;
+ /* try to skip the exit call */
+ rv=ptrace(PTRACE_SYSCALL, pid, PTRACE_SYSCALL_SKIPEXIT, 0);
+ if (rv < 0)
+ goto out;
+ /* wait for the next stop */
+ if(waitpid(pid, &status, WUNTRACED) < 0)
+ goto out;
+ /* if feature is already 0 it means that this is the exit call,
+ * and it has not been skipped, otherwise this is the
+ * entry call for the system call "time" */
+ if (feature<PTRACE_SYSCALL_SKIPEXIT)
+ goto out;
+ /* restart (time) and and try to skip the entire call */
+ rv=ptrace(PTRACE_SYSCALL, pid, PTRACE_SYSCALL_SKIPCALL, 0);
+ if(waitpid(pid, &status, WUNTRACED) < 0)
+ return 0;
+out:
+ ptrace(PTRACE_KILL,pid,0,0);
+ /* eliminate zombie */
+ if(waitpid(pid, &status, WUNTRACED) < 0)
+ return 0;
+ return feature;
+}
+
+static int __init check_sysptvm(void)
+{
+ int feature=test_ptrace_sysptvm();
+
+ non_fatal("Checking ptrace new tags for syscall emulation...");
+ if (feature==PTRACE_SYSCALL_SKIPCALL) {
+ sysptvm_supported=1;
+ non_fatal("OK");
+ if (!force_sysptvm_disabled) {
+ set_using_sysptvm(PTRACE_SYSCALL_SKIPCALL);
+ non_fatal("\n");
+ return 1;
+ } else {
+ non_fatal(" (disabled)\n");
+ return 0;
+ }
+ } else
+ non_fatal("unsupported\n");
+ return 0;
+}
+
static void __init check_ptrace(void)
{
int pid, syscall, n, status;
@@ -330,7 +455,8 @@
}
stop_ptraced_child(pid, 0, 1);
non_fatal("OK\n");
- check_sysemu();
+ if (use_sysemu || !check_sysptvm())
+ check_sysemu();
}
extern void check_tmpexec(void);
--
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