[patch 22/26] i386: fix infinite loop with singlestep int80 syscalls

Greg KH
2007-07-31T04:39:25Z

[-- Attachment #1: i386-fix-infinite-loop-with-singlestep-int80-syscalls.patch --]
[-- Type: text/plain, Size: 2921 bytes --]

-stable review patch. If anyone has any objections, please let us know.

------------------

The commit 635cf99a80f4ebee59d70eb64bb85ce829e4591f introduced a
regression. Executing a ptrace single step after certain int80
accesses will infinitely loop and never advance the PC.

The TIF_SINGLESTEP check should be done on the return from the syscall
and not before it.

The new test case is below:

/* Test whether singlestep through an int80 syscall works.
*/
#define _GNU_SOURCE
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ptrace.h>
#include <sys/wait.h>
#include <sys/mman.h>
#include <asm/user.h>
#include <string.h>

static int child, status;
static struct user_regs_struct regs;

static void do_child()
{
char str[80] = "child: int80 test\n";

ptrace(PTRACE_TRACEME, 0, 0, 0);
kill(getpid(), SIGUSR1);
write(fileno(stdout),str,strlen(str));
asm ("int $0x80" : : "a" (20)); /* getpid */
}

static void do_parent()
{
unsigned long eip, expected = 0;
again:
waitpid(child, &status, 0);
if (WIFEXITED(status) || WIFSIGNALED(status))
return;

if (WIFSTOPPED(status)) {
ptrace(PTRACE_GETREGS, child, 0, &regs);
eip = regs.eip;
if (expected)
fprintf(stderr, "child stop @ %08lx, expected %08lx %s\n",
eip, expected,
eip == expected ? "" : " <== ERROR");

if (*(unsigned short *)eip == 0x80cd) {
fprintf(stderr, "int 0x80 at %08x\n", (unsigned int)eip);
expected = eip + 2;
} else
expected = 0;

ptrace(PTRACE_SINGLESTEP, child, NULL, NULL);
}
goto again;
}

int main(int argc, char * const argv[])
{
child = fork();
if (child)
do_parent();
else
do_child();
return 0;
}

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Chuck Ebbert <cebbert@redhat.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
arch/i386/kernel/entry.S | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

--- linux-2.6.21.6.orig/arch/i386/kernel/entry.S
+++ linux-2.6.21.6/arch/i386/kernel/entry.S
@@ -371,10 +371,6 @@ ENTRY(system_call)
CFI_ADJUST_CFA_OFFSET 4
SAVE_ALL
GET_THREAD_INFO(%ebp)
- testl $TF_MASK,PT_EFLAGS(%esp)
- jz no_singlestep
- orl $_TIF_SINGLESTEP,TI_flags(%ebp)
-no_singlestep:
# system call tracing in operation / emulation
/* Note, _TIF_SECCOMP is bit number 8, and so it needs testw and not testb */
testw $(_TIF_SYSCALL_EMU|_TIF_SYSCALL_TRACE|_TIF_SECCOMP|_TIF_SYSCALL_AUDIT),TI_flags(%ebp)
@@ -389,6 +385,10 @@ syscall_exit:
# setting need_resched or sigpending
# between sampling and the iret
TRACE_IRQS_OFF
+ testl $TF_MASK,PT_EFLAGS(%esp) # If tracing set singlestep flag on exit
+ jz no_singlestep
+ orl $_TIF_SINGLESTEP,TI_flags(%ebp)
+no_singlestep:
movl TI_flags(%ebp), %ecx
testw $_TIF_ALLWORK_MASK, %cx # current->work
jne syscall_exit_work

--