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i386: fix regression, endless loop in ptrace singlestep over an int80

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The commit 635cf99a80 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.

I loops on each single step on the pop right after the int80 which writes out
to the console.  At that point you can issue as many single steps as you want
and it will not advance any further.

The 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: <stable@kernel.org>
Cc: Chuck Ebbert <76306.1226@compuserve.com>
Acked-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Jason Wessel 2007-07-06 02:39:50 -07:00 committed by Linus Torvalds
parent ef7320edb1
commit 1e2e99f0e4
1 changed files with 4 additions and 4 deletions
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8
arch/i386/kernel/entry.S
View File

@ -367,10 +367,6 @@ 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)
@ -385,6 +381,10 @@ 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