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x86: ia32 syscall restart fix

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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: Roland McGrath <roland@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Roland McGrath 2008-02-28 19:57:07 -08:00 committed by Ingo Molnar
parent 9a46d7e5b6
commit 40f0933d51
2 changed files with 41 additions and 6 deletions
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9
arch/x86/kernel/ptrace.c
View File

@ -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);

38
arch/x86/kernel/signal_64.c
View File

@ -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: