On Wed, Feb 13, 2013 at 4:16 PM, Andrey Vagin <avagin@xxxxxxxxxx> wrote:
> This patch adds a new ptrace request PTRACE_PEEKSIGINFO.
>
> This request is used to retrieve information about a signal with the
> specified sequence number. A siginfo_t structure is copied from the child
> to location data in the parent.
>
> The low 16 bits of addr contains a sequence number of signal in a queue:
I think 16 bits is probably not enough.... Already, on the "out of the
box" system that I have at hand, one can queue more than 2^16-1
signals:
$ cat /proc/$$/status | grep SigQ
SigQ: 2/126065
Cheers,
Michael
> All other bits of addr is used for flags. Currently here is only one
> flag PTRACE_PEEK_SHARED for dumping signals from process-wide shared
> queue. If this flag is not set, a signal is read from a per-thread
> queue. A result siginfo contains a kernel part of si_code which usually
> striped, but it's required for queuing the same siginfo back during
> restore of pending signals.
>
> If a signal with the specified sequence number doesn't exist, ptrace
> returns ENOENT.
>
> This functionality is required for checkpointing pending signals.
>
> The prototype of this code was developed by Oleg Nesterov.
>
> Cc: Roland McGrath <roland@xxxxxxxxxx>
> Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
> Cc: David Howells <dhowells@xxxxxxxxxx>
> Cc: Dave Jones <davej@xxxxxxxxxx>
> Cc: "Michael Kerrisk (man-pages)" <mtk.manpages@xxxxxxxxx>
> Cc: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Andrey Vagin <avagin@xxxxxxxxxx>
> ---
> include/uapi/linux/ptrace.h | 9 +++++++
> kernel/ptrace.c | 64 +++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 73 insertions(+)
>
> diff --git a/include/uapi/linux/ptrace.h b/include/uapi/linux/ptrace.h
> index 022ab18..5d851d5 100644
> --- a/include/uapi/linux/ptrace.h
> +++ b/include/uapi/linux/ptrace.h
> @@ -52,6 +52,15 @@
> #define PTRACE_INTERRUPT 0x4207
> #define PTRACE_LISTEN 0x4208
>
> +#define PTRACE_PEEKSIGINFO 0x4209
> +
> +/*
> + * The lower 16 bits of addr is a sequence number of a signal.
> + * All other bits can be used for flags.
> + */
> +#define PTRACE_PEEKSIGINFO_FLAGS_MASK (~0UL << 16)
> +#define PTRACE_PEEK_SHARED (1UL << 31)
> +
> /* Wait extended result codes for the above trace options. */
> #define PTRACE_EVENT_FORK 1
> #define PTRACE_EVENT_VFORK 2
> diff --git a/kernel/ptrace.c b/kernel/ptrace.c
> index 1599157..27fd31a 100644
> --- a/kernel/ptrace.c
> +++ b/kernel/ptrace.c
> @@ -579,6 +579,40 @@ static int ptrace_setsiginfo(struct task_struct *child, const siginfo_t *info)
> return error;
> }
>
> +#ifdef CONFIG_CHECKPOINT_RESTORE
> +static int ptrace_peek_siginfo(struct task_struct *child,
> + unsigned long addr, siginfo_t *siginfo)
> +{
> + struct sigpending *pending;
> + struct sigqueue *q;
> + unsigned long flags;
> + unsigned int nr;
> + int ret = -ENOENT;
> +
> + nr = addr & ~PTRACE_PEEKSIGINFO_FLAGS_MASK;
> + flags = addr & PTRACE_PEEKSIGINFO_FLAGS_MASK;
> +
> + if (flags & PTRACE_PEEK_SHARED)
> + pending = &child->signal->shared_pending;
> + else
> + pending = &child->pending;
> +
> + if (flags & ~PTRACE_PEEK_SHARED)
> + return -EINVAL; /* unknown flags */
> +
> + spin_lock_irq(&child->sighand->siglock);
> + list_for_each_entry(q, &pending->list, list) {
> + if (!nr--) {
> + copy_siginfo(siginfo, &q->info);
> + ret = 0;
> + break;
> + }
> + }
> + spin_unlock_irq(&child->sighand->siglock);
> +
> + return ret;
> +}
> +#endif
>
> #ifdef PTRACE_SINGLESTEP
> #define is_singlestep(request) ((request) == PTRACE_SINGLESTEP)
> @@ -703,6 +737,21 @@ int ptrace_request(struct task_struct *child, long request,
> ret = put_user(child->ptrace_message, datalp);
> break;
>
> +#ifdef CONFIG_CHECKPOINT_RESTORE
> + case PTRACE_PEEKSIGINFO:
> + {
> + siginfo_t __user *uinfo = (siginfo_t __user *) data;
> +
> + ret = ptrace_peek_siginfo(child, addr, &siginfo);
> +
> + if (!ret)
> + ret = copy_siginfo_to_user(uinfo, &siginfo);
> + if (!ret)
> + ret = __put_user(siginfo.si_code, &uinfo->si_code);
> + break;
> + }
> +#endif
> +
> case PTRACE_GETSIGINFO:
> ret = ptrace_getsiginfo(child, &siginfo);
> if (!ret)
> @@ -959,6 +1008,21 @@ int compat_ptrace_request(struct task_struct *child, compat_long_t request,
> ret = put_user((compat_ulong_t) child->ptrace_message, datap);
> break;
>
> +#ifdef CONFIG_CHECKPOINT_RESTORE
> + case PTRACE_PEEKSIGINFO:
> + {
> + compat_siginfo_t __user *uinfo = compat_ptr(data);
> +
> + ret = ptrace_peek_siginfo(child, addr, &siginfo);
> +
> + if (!ret)
> + ret = copy_siginfo_to_user32(uinfo, &siginfo);
> + if (!ret)
> + ret = __put_user(siginfo.si_code, &uinfo->si_code);
> + break;
> + }
> +#endif
> +
> case PTRACE_GETSIGINFO:
> ret = ptrace_getsiginfo(child, &siginfo);
> if (!ret)
> --
> 1.7.11.7
>
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Author of "The Linux Programming Interface"; http://man7.org/tlpi/
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