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Subject[PATCH v7 3.2-rc2 26/30] uprobes: introduce uprobe_deny_signal()

A not-UTASK_RUNNING task obviously can't handle the signals, neither
it should stop/freeze/etc. It must not even exit if it was
SIGKILL'ed

This patch adds the new hook, uprobe_deny_signal(), called by
get_signal_to_deliver(). It simply clears TIF_SIGPENDING to ensure
that this thread can do nothing connected to signals until it
becomes UTASK_RUNNING.

We also change post_xol() path to do recalc_sigpending() before
return to user-mode, this ensures the signal can't be lost.

Original-patch-from: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
---
include/linux/uprobes.h | 5 +++++
kernel/signal.c | 3 +++
kernel/uprobes.c | 23 +++++++++++++++++++++++
3 files changed, 31 insertions(+), 0 deletions(-)

diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index 70d639c..8d12c06 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -129,6 +129,7 @@ extern unsigned long __weak get_uprobe_bkpt_addr(struct pt_regs *regs);
extern int uprobe_post_notifier(struct pt_regs *regs);
extern int uprobe_bkpt_notifier(struct pt_regs *regs);
extern void uprobe_notify_resume(struct pt_regs *regs);
+extern bool uprobe_deny_signal(void);
#else /* CONFIG_UPROBES is not defined */
static inline int register_uprobe(struct inode *inode, loff_t offset,
struct uprobe_consumer *consumer)
@@ -149,6 +150,10 @@ static inline void munmap_uprobe(struct vm_area_struct *vma)
static inline void uprobe_notify_resume(struct pt_regs *regs)
{
}
+static inline bool uprobe_deny_signal(void)
+{
+ return false;
+}
static inline unsigned long get_uprobe_bkpt_addr(struct pt_regs *regs)
{
return 0;
diff --git a/kernel/signal.c b/kernel/signal.c
index b3f78d0..5d68510 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2149,6 +2149,9 @@ int get_signal_to_deliver(siginfo_t *info, struct k_sigaction *return_ka,
struct signal_struct *signal = current->signal;
int signr;

+ if (unlikely(uprobe_deny_signal()))
+ return 0;
+
relock:
/*
* We'll jump back here after any time we were stopped in TASK_STOPPED.
diff --git a/kernel/uprobes.c b/kernel/uprobes.c
index 50cde86..3e7c4c5 100644
--- a/kernel/uprobes.c
+++ b/kernel/uprobes.c
@@ -1312,6 +1312,25 @@ static int pre_ssout(struct uprobe *uprobe, struct pt_regs *regs,
return -EFAULT;
}

+bool uprobe_deny_signal(void)
+{
+ struct task_struct *tsk = current;
+ struct uprobe_task *utask = tsk->utask;
+
+ if (likely(!utask || !utask->active_uprobe))
+ return false;
+
+ WARN_ON_ONCE(utask->state != UTASK_SSTEP);
+
+ if (signal_pending(tsk)) {
+ spin_lock_irq(&tsk->sighand->siglock);
+ clear_tsk_thread_flag(tsk, TIF_SIGPENDING);
+ spin_unlock_irq(&tsk->sighand->siglock);
+ }
+
+ return true;
+}
+
/*
* uprobe_notify_resume gets called in task context just before returning
* to userspace.
@@ -1371,6 +1390,10 @@ void uprobe_notify_resume(struct pt_regs *regs)
utask->state = UTASK_RUNNING;
user_disable_single_step(current);
xol_free_insn_slot(current);
+
+ spin_lock_irq(&current->sighand->siglock);
+ recalc_sigpending(); /* see uprobe_deny_signal() */
+ spin_unlock_irq(&current->sighand->siglock);
}
return;



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