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Subject[PATCH v2 8/9] uprobes/x86: Send SIGILL if arch_uprobe_post_xol() fails
Currently the error from arch_uprobe_post_xol() is silently ignored.
This doesn't look good and this can lead to the hard-to-debug problems.

1. Change handle_singlestep() to loudly complain and send SIGILL.

Note: this only affects x86, ppc/arm can't fail.

2. Change arch_uprobe_post_xol() to call arch_uprobe_abort_xol() and
avoid TF games if it is going to return an error.

This can help to to analyze the problem, if nothing else we should
not report ->ip = xol_slot in the core-file.

Note: this means that handle_riprel_post_xol() can be called twice,
but this is fine because it is idempotent.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
arch/x86/kernel/uprobes.c | 16 ++++++++++++----
kernel/events/uprobes.c | 8 +++++++-
2 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 08cdb82..e72903e 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -594,6 +594,15 @@ int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
struct uprobe_task *utask = current->utask;

WARN_ON_ONCE(current->thread.trap_nr != UPROBE_TRAP_NR);
+
+ if (auprobe->ops->post_xol) {
+ int err = auprobe->ops->post_xol(auprobe, regs);
+ if (err) {
+ arch_uprobe_abort_xol(auprobe, regs);
+ return err;
+ }
+ }
+
current->thread.trap_nr = utask->autask.saved_trap_nr;
/*
* arch_uprobe_pre_xol() doesn't save the state of TIF_BLOCKSTEP
@@ -605,8 +614,6 @@ int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
else if (!(auprobe->fixups & UPROBE_FIX_SETF))
regs->flags &= ~X86_EFLAGS_TF;

- if (auprobe->ops->post_xol)
- return auprobe->ops->post_xol(auprobe, regs);
return 0;
}

@@ -641,8 +648,9 @@ int arch_uprobe_exception_notify(struct notifier_block *self, unsigned long val,

/*
* This function gets called when XOL instruction either gets trapped or
- * the thread has a fatal signal, so reset the instruction pointer to its
- * probed address.
+ * the thread has a fatal signal, or if arch_uprobe_post_xol() failed.
+ * Reset the instruction pointer to its probed address for the potential
+ * restart or for post mortem analysis.
*/
void arch_uprobe_abort_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
{
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 7a3e14e..2adbc97 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1858,10 +1858,11 @@ out:
static void handle_singlestep(struct uprobe_task *utask, struct pt_regs *regs)
{
struct uprobe *uprobe;
+ int err = 0;

uprobe = utask->active_uprobe;
if (utask->state == UTASK_SSTEP_ACK)
- arch_uprobe_post_xol(&uprobe->arch, regs);
+ err = arch_uprobe_post_xol(&uprobe->arch, regs);
else if (utask->state == UTASK_SSTEP_TRAPPED)
arch_uprobe_abort_xol(&uprobe->arch, regs);
else
@@ -1875,6 +1876,11 @@ static void handle_singlestep(struct uprobe_task *utask, struct pt_regs *regs)
spin_lock_irq(&current->sighand->siglock);
recalc_sigpending(); /* see uprobe_deny_signal() */
spin_unlock_irq(&current->sighand->siglock);
+
+ if (unlikely(err)) {
+ uprobe_warn(current, "execute the probed insn, sending SIGILL.");
+ force_sig_info(SIGILL, SEND_SIG_FORCED, current);
+ }
}

/*
--
1.5.5.1


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