Commit 40f0933d authored by Roland McGrath's avatar Roland McGrath Committed by Ingo Molnar
Browse files

x86: ia32 syscall restart fix 



The code to restart syscalls after signals depends on checking for a
negative orig_ax, and for particular negative -ERESTART* values in ax.
These fields are 64 bits and for a 32-bit task they get zero-extended.
The syscall restart behavior is lost, a regression from a native 32-bit
kernel and from 64-bit tasks' behavior.

This patch fixes the problem by doing sign-extension where it matters.

For orig_ax, the only time the value should be -1 but winds up as
0x0ffffffff is via a 32-bit ptrace call. So the patch changes ptrace to
sign-extend the 32-bit orig_eax value when it's stored; it doesn't
change the checks on orig_ax, though it uses the new current_syscall()
inline to better document the subtle importance of the used of
signedness there.

The ax value is stored a lot of ways and it seems hard to get them all
sign-extended at their origins. So for that, we use the
current_syscall_ret() to sign-extend it only for 32-bit tasks at the
time of the -ERESTART* comparisons.

Signed-off-by: default avatarRoland McGrath <roland@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 9a46d7e5

arch/x86/kernel/ptrace.c

+8 −1
Original line number Diff line number Diff line
@@ -1055,10 +1055,17 @@ static int putreg32(struct task_struct *child, unsigned regno, u32 value) 
	R32(esi, si);

	R32(ebp, bp);

	R32(eax, ax);

	R32(orig_eax, orig_ax);

	R32(eip, ip);

	R32(esp, sp);



	case offsetof(struct user32, regs.orig_eax):

		/*

		 * Sign-extend the value so that orig_eax = -1

		 * causes (long)orig_ax < 0 tests to fire correctly.

		 */

		regs->orig_ax = (long) (s32) value;

		break;



	case offsetof(struct user32, regs.eflags):

		return set_flags(child, value);

arch/x86/kernel/signal_64.c

+33 −5
Original line number Diff line number Diff line
@@ -310,6 +310,35 @@ give_sigsegv: 
	return -EFAULT;

}



/*

 * Return -1L or the syscall number that @regs is executing.

 */

static long current_syscall(struct pt_regs *regs)

{

	/*

	 * We always sign-extend a -1 value being set here,

	 * so this is always either -1L or a syscall number.

	 */

	return regs->orig_ax;

}



/*

 * Return a value that is -EFOO if the system call in @regs->orig_ax

 * returned an error.  This only works for @regs from @current.

 */

static long current_syscall_ret(struct pt_regs *regs)

{

#ifdef CONFIG_IA32_EMULATION

	if (test_thread_flag(TIF_IA32))

		/*

		 * Sign-extend the value so (int)-EFOO becomes (long)-EFOO

		 * and will match correctly in comparisons.

		 */

		return (int) regs->ax;

#endif

	return regs->ax;

}



/*

 * OK, we're invoking a handler

 */
@@ -327,9 +356,9 @@ handle_signal(unsigned long sig, siginfo_t *info, struct k_sigaction *ka, 
#endif



	/* Are we from a system call? */

	if ((long)regs->orig_ax >= 0) {

	if (current_syscall(regs) >= 0) {

		/* If so, check system call restarting.. */

		switch (regs->ax) {

		switch (current_syscall_ret(regs)) {

		        case -ERESTART_RESTARTBLOCK:

			case -ERESTARTNOHAND:

				regs->ax = -EINTR;
@@ -426,10 +455,9 @@ static void do_signal(struct pt_regs *regs) 
	}



	/* Did we come from a system call? */

	if ((long)regs->orig_ax >= 0) {

	if (current_syscall(regs) >= 0) {

		/* Restart the system call - no handlers present */

		long res = regs->ax;

		switch (res) {

		switch (current_syscall_ret(regs)) {

		case -ERESTARTNOHAND:

		case -ERESTARTSYS:

		case -ERESTARTNOINTR:

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