[patch] really-ptrace-single-step2 ...
From: Davide Libenzi
Date: Tue May 11 2004 - 18:33:42 EST
This patch lets a ptrace process on x86 to "see" the instruction
following the INT #80h op. This has been tested on 2.6.6 using the
appended test source. Running over this:
80485a9: b8 14 00 00 00 mov $0x14,%eax
80485ae: cd 80 int $0x80
80485b0: 89 45 ec mov %eax,0xffffffec(%ebp)
80485b3: eb f4 jmp 80485a9 <main+0x85>
it produces:
waiting ...
done: pid=12387 status=1407
sig=5
EIP=0x080485a9
waiting ...
done: pid=12387 status=1407
sig=5
EIP=0x080485ae
waiting ...
done: pid=12387 status=1407
sig=5
EIP=0x080485b0
waiting ...
done: pid=12387 status=1407
sig=5
EIP=0x080485b3
- Davide
----------------------------- TEST ------------------------------
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/ptrace.h>
#include <sys/wait.h>
#include <linux/user.h>
#include <linux/unistd.h>
int main(int ac, char **av) {
int i, status, res;
long start, end;
pid_t cpid, pid;
struct user_regs_struct ur;
struct sigaction sa;
sigemptyset(&sa.sa_mask);
sa.sa_flags = 0;
sa.sa_handler = SIG_DFL;
sigaction(SIGCHLD, &sa, NULL);
printf("nargs=%d\n", ac);
if (ac == 1)
goto tracer;
printf("arg=%s\n", av[1]);
loop:
__asm__ volatile ("int $0x80"
: "=a" (res)
: "0" (__NR_getpid));
goto loop;
endloop:
exit(0);
tracer:
if ((cpid = fork()) != 0)
goto parent;
printf("child=%d\n", getpid());
ptrace(PTRACE_TRACEME, 0, NULL, NULL);
execl(av[0], av[0], "child", NULL);
exit(0);
parent:
start = (long) &&loop;
end = (long) &&endloop;
printf("pchild=%d\n", cpid);
for (;;) {
pid = wait(&status);
if (pid != cpid)
continue;
res = WSTOPSIG(status);
if (ptrace(PTRACE_GETREGS, pid, NULL, &ur)) {
printf("[%d] error: ptrace(PTRACE_GETREGS, %d)\n",
pid, pid);
return 1;
}
if (ptrace(PTRACE_SINGLESTEP, pid, NULL, res != SIGTRAP ? res: 0)) {
perror("ptrace(PTRACE_SINGLESTEP)");
return 1;
}
if (ur.eip >= start && ur.eip <= end)
break;
}
for (i = 0; i < 15; i++) {
printf("waiting ...\n");
pid = wait(&status);
printf("done: pid=%d status=%d\n", pid, status);
if (pid != cpid)
continue;
res = WSTOPSIG(status);
printf("sig=%d\n", res);
if (ptrace(PTRACE_GETREGS, pid, NULL, &ur)) {
printf("[%d] error: ptrace(PTRACE_GETREGS, %d)\n",
pid, pid);
return 1;
}
printf("EIP=0x%08x\n", ur.eip);
if (ptrace(PTRACE_SINGLESTEP, pid, NULL, res != SIGTRAP ? res: 0)) {
perror("ptrace(PTRACE_SINGLESTEP)");
return 1;
}
}
if (ptrace(PTRACE_CONT, cpid, NULL, SIGKILL)) {
perror("ptrace(PTRACE_SINGLESTEP)");
return 1;
}
return 0;
}
--------------------------- PATCH ----------------------------------
arch/i386/kernel/entry.S | 2 +-
arch/i386/kernel/ptrace.c | 7 ++++++-
include/asm-i386/thread_info.h | 2 +-
3 files changed, 8 insertions(+), 3 deletions(-)
Index: arch/i386/kernel/entry.S
===================================================================
RCS file: /usr/src/bkcvs/linux-2.5/arch/i386/kernel/entry.S,v
retrieving revision 1.83
diff -u -r1.83 entry.S
--- a/arch/i386/kernel/entry.S 12 Apr 2004 20:29:12 -0000 1.83
+++ b/arch/i386/kernel/entry.S 11 May 2004 18:49:56 -0000
@@ -354,7 +354,7 @@
# perform syscall exit tracing
ALIGN
syscall_exit_work:
- testb $(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT), %cl
+ testb $(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SINGLESTEP), %cl
jz work_pending
sti # could let do_syscall_trace() call
# schedule() instead
Index: arch/i386/kernel/ptrace.c
===================================================================
RCS file: /usr/src/bkcvs/linux-2.5/arch/i386/kernel/ptrace.c,v
retrieving revision 1.23
diff -u -r1.23 ptrace.c
--- a/arch/i386/kernel/ptrace.c 10 May 2004 21:25:52 -0000 1.23
+++ b/arch/i386/kernel/ptrace.c 11 May 2004 21:33:20 -0000
@@ -147,6 +147,7 @@
{
long tmp;
+ clear_tsk_thread_flag(child, TIF_SINGLESTEP);
tmp = get_stack_long(child, EFL_OFFSET) & ~TRAP_FLAG;
put_stack_long(child, EFL_OFFSET, tmp);
}
@@ -369,6 +370,7 @@
else {
clear_tsk_thread_flag(child, TIF_SYSCALL_TRACE);
}
+ clear_tsk_thread_flag(child, TIF_SINGLESTEP);
child->exit_code = data;
/* make sure the single step bit is not set. */
tmp = get_stack_long(child, EFL_OFFSET) & ~TRAP_FLAG;
@@ -390,6 +392,7 @@
if (child->state == TASK_ZOMBIE) /* already dead */
break;
child->exit_code = SIGKILL;
+ clear_tsk_thread_flag(child, TIF_SINGLESTEP);
/* make sure the single step bit is not set. */
tmp = get_stack_long(child, EFL_OFFSET) & ~TRAP_FLAG;
put_stack_long(child, EFL_OFFSET, tmp);
@@ -410,6 +413,7 @@
}
tmp = get_stack_long(child, EFL_OFFSET) | TRAP_FLAG;
put_stack_long(child, EFL_OFFSET, tmp);
+ set_tsk_thread_flag(child, TIF_SINGLESTEP);
child->exit_code = data;
/* give it a chance to run. */
wake_up_process(child);
@@ -534,7 +538,8 @@
audit_syscall_exit(current, regs->eax);
}
- if (!test_thread_flag(TIF_SYSCALL_TRACE))
+ if (!test_thread_flag(TIF_SYSCALL_TRACE) &&
+ !test_thread_flag(TIF_SINGLESTEP))
return;
if (!(current->ptrace & PT_PTRACED))
return;
Index: include/asm-i386/thread_info.h
===================================================================
RCS file: /usr/src/bkcvs/linux-2.5/include/asm-i386/thread_info.h,v
retrieving revision 1.19
diff -u -r1.19 thread_info.h
--- a/include/asm-i386/thread_info.h 12 Apr 2004 20:29:12 -0000 1.19
+++ b/include/asm-i386/thread_info.h 11 May 2004 18:47:03 -0000
@@ -165,7 +165,7 @@
/* work to do on interrupt/exception return */
#define _TIF_WORK_MASK \
- (0x0000FFFF & ~(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT))
+ (0x0000FFFF & ~(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SINGLESTEP))
#define _TIF_ALLWORK_MASK 0x0000FFFF /* work to do on any return to u-space */
/*
-
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