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: Roland McGrath <roland@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 8f64abe..d5904ee 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -1055,10 +1055,17 @@
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);
diff --git a/arch/x86/kernel/signal_64.c b/arch/x86/kernel/signal_64.c
index 56b72fb..1c83e51 100644
--- a/arch/x86/kernel/signal_64.c
+++ b/arch/x86/kernel/signal_64.c
@@ -311,6 +311,35 @@
}
/*
+ * 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 @@
#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 @@
}
/* 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: