On Tue, Jun 11, 2013 at 06:42:28PM +0200, Robert Richter wrote:
> From: Borislav Petkov <b...@alien8.de>
>
> Add the needed pieces for persistent events which makes them
> process-agnostic. Also, make their buffers read-only when mmaping them
> from userspace.
>
> While at it, do not return a void function, as caught by Fengguang's
> build robot.
>
> Changes made by Robert Richter <robert.rich...@linaro.org>:
>
> * mmap should return EACCES error if fd can not be opened writable.
> This error code also helps userland to map buffers readonly on
> failure.
>
> Signed-off-by: Borislav Petkov <b...@suse.de>
> [ Return -EACCES if mapped buffers must be readonly ]
> Signed-off-by: Robert Richter <robert.rich...@linaro.org>
> Signed-off-by: Robert Richter <r...@kernel.org>
> ---
> include/uapi/linux/perf_event.h | 3 ++-
> kernel/events/core.c | 10 +++++++++-
> 2 files changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index fb104e5..6032361 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -272,8 +272,9 @@ struct perf_event_attr {
>
> exclude_callchain_kernel : 1, /* exclude kernel
> callchains */
> exclude_callchain_user : 1, /* exclude user
> callchains */
> + persistent : 1, /* always-on event */
>
> - __reserved_1 : 41;
> + __reserved_1 : 40;
>
> union {
> __u32 wakeup_events; /* wakeup every n events */
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index b790ab6..a13e457 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -3713,6 +3713,11 @@ static void perf_mmap_close(struct vm_area_struct *vma)
> {
> struct perf_event *event = vma->vm_file->private_data;
>
> + if (event->attr.persistent) {
> + atomic_dec(&event->mmap_count);
> + return;
> + }
> +
> if (atomic_dec_and_mutex_lock(&event->mmap_count, &event->mmap_mutex)) {
> unsigned long size = perf_data_size(event->rb);
> struct user_struct *user = event->mmap_user;
> @@ -3756,9 +3761,12 @@ static int perf_mmap(struct file *file, struct
> vm_area_struct *vma)
> if (event->cpu == -1 && event->attr.inherit)
> return -EINVAL;
>
> - if (!(vma->vm_flags & VM_SHARED))
> + if (!(vma->vm_flags & VM_SHARED) && !event->attr.persistent)
> return -EINVAL;
>
> + if (event->attr.persistent && (vma->vm_flags & VM_WRITE))
> + return -EACCES;
> +
> vma_size = vma->vm_end - vma->vm_start;
> nr_pages = (vma_size / PAGE_SIZE) - 1;
I find this patch incomplete for its asymmetric; there a dec, but not an
implied inc.
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