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    Subject[PATCH 3.4 08/32] connector: improved unaligned access error fix
    Date
    3.4-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Chris Metcalf <cmetcalf@tilera.com>

    [ Upstream commit 1ca1a4cf59ea343a1a70084fe7cc96f37f3cf5b1 ]

    In af3e095a1fb4, Erik Jacobsen fixed one type of unaligned access
    bug for ia64 by converting a 64-bit write to use put_unaligned().
    Unfortunately, since gcc will convert a short memset() to a series
    of appropriately-aligned stores, the problem is now visible again
    on tilegx, where the memset that zeros out proc_event is converted
    to three 64-bit stores, causing an unaligned access panic.

    A better fix for the original problem is to ensure that proc_event
    is aligned to 8 bytes here. We can do that relatively easily by
    arranging to start the struct cn_msg aligned to 8 bytes and then
    offset by 4 bytes. Doing so means that the immediately following
    proc_event structure is then correctly aligned to 8 bytes.

    The result is that the memset() stores are now aligned, and as an
    added benefit, we can remove the put_unaligned() calls in the code.

    Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/connector/cn_proc.c | 66 ++++++++++++++++++++++++++------------------
    1 file changed, 39 insertions(+), 27 deletions(-)

    --- a/drivers/connector/cn_proc.c
    +++ b/drivers/connector/cn_proc.c
    @@ -31,11 +31,23 @@
    #include <linux/ptrace.h>
    #include <linux/atomic.h>

    -#include <asm/unaligned.h>
    -
    #include <linux/cn_proc.h>

    -#define CN_PROC_MSG_SIZE (sizeof(struct cn_msg) + sizeof(struct proc_event))
    +/*
    + * Size of a cn_msg followed by a proc_event structure. Since the
    + * sizeof struct cn_msg is a multiple of 4 bytes, but not 8 bytes, we
    + * add one 4-byte word to the size here, and then start the actual
    + * cn_msg structure 4 bytes into the stack buffer. The result is that
    + * the immediately following proc_event structure is aligned to 8 bytes.
    + */
    +#define CN_PROC_MSG_SIZE (sizeof(struct cn_msg) + sizeof(struct proc_event) + 4)
    +
    +/* See comment above; we test our assumption about sizeof struct cn_msg here. */
    +static inline struct cn_msg *buffer_to_cn_msg(__u8 *buffer)
    +{
    + BUILD_BUG_ON(sizeof(struct cn_msg) != 20);
    + return (struct cn_msg *)(buffer + 4);
    +}

    static atomic_t proc_event_num_listeners = ATOMIC_INIT(0);
    static struct cb_id cn_proc_event_id = { CN_IDX_PROC, CN_VAL_PROC };
    @@ -55,19 +67,19 @@ void proc_fork_connector(struct task_str
    {
    struct cn_msg *msg;
    struct proc_event *ev;
    - __u8 buffer[CN_PROC_MSG_SIZE];
    + __u8 buffer[CN_PROC_MSG_SIZE] __aligned(8);
    struct timespec ts;
    struct task_struct *parent;

    if (atomic_read(&proc_event_num_listeners) < 1)
    return;

    - msg = (struct cn_msg*)buffer;
    + msg = buffer_to_cn_msg(buffer);
    ev = (struct proc_event*)msg->data;
    memset(&ev->event_data, 0, sizeof(ev->event_data));
    get_seq(&msg->seq, &ev->cpu);
    ktime_get_ts(&ts); /* get high res monotonic timestamp */
    - put_unaligned(timespec_to_ns(&ts), (__u64 *)&ev->timestamp_ns);
    + ev->timestamp_ns = timespec_to_ns(&ts);
    ev->what = PROC_EVENT_FORK;
    rcu_read_lock();
    parent = rcu_dereference(task->real_parent);
    @@ -90,17 +102,17 @@ void proc_exec_connector(struct task_str
    struct cn_msg *msg;
    struct proc_event *ev;
    struct timespec ts;
    - __u8 buffer[CN_PROC_MSG_SIZE];
    + __u8 buffer[CN_PROC_MSG_SIZE] __aligned(8);

    if (atomic_read(&proc_event_num_listeners) < 1)
    return;

    - msg = (struct cn_msg*)buffer;
    + msg = buffer_to_cn_msg(buffer);
    ev = (struct proc_event*)msg->data;
    memset(&ev->event_data, 0, sizeof(ev->event_data));
    get_seq(&msg->seq, &ev->cpu);
    ktime_get_ts(&ts); /* get high res monotonic timestamp */
    - put_unaligned(timespec_to_ns(&ts), (__u64 *)&ev->timestamp_ns);
    + ev->timestamp_ns = timespec_to_ns(&ts);
    ev->what = PROC_EVENT_EXEC;
    ev->event_data.exec.process_pid = task->pid;
    ev->event_data.exec.process_tgid = task->tgid;
    @@ -116,14 +128,14 @@ void proc_id_connector(struct task_struc
    {
    struct cn_msg *msg;
    struct proc_event *ev;
    - __u8 buffer[CN_PROC_MSG_SIZE];
    + __u8 buffer[CN_PROC_MSG_SIZE] __aligned(8);
    struct timespec ts;
    const struct cred *cred;

    if (atomic_read(&proc_event_num_listeners) < 1)
    return;

    - msg = (struct cn_msg*)buffer;
    + msg = buffer_to_cn_msg(buffer);
    ev = (struct proc_event*)msg->data;
    memset(&ev->event_data, 0, sizeof(ev->event_data));
    ev->what = which_id;
    @@ -144,7 +156,7 @@ void proc_id_connector(struct task_struc
    rcu_read_unlock();
    get_seq(&msg->seq, &ev->cpu);
    ktime_get_ts(&ts); /* get high res monotonic timestamp */
    - put_unaligned(timespec_to_ns(&ts), (__u64 *)&ev->timestamp_ns);
    + ev->timestamp_ns = timespec_to_ns(&ts);

    memcpy(&msg->id, &cn_proc_event_id, sizeof(msg->id));
    msg->ack = 0; /* not used */
    @@ -158,17 +170,17 @@ void proc_sid_connector(struct task_stru
    struct cn_msg *msg;
    struct proc_event *ev;
    struct timespec ts;
    - __u8 buffer[CN_PROC_MSG_SIZE];
    + __u8 buffer[CN_PROC_MSG_SIZE] __aligned(8);

    if (atomic_read(&proc_event_num_listeners) < 1)
    return;

    - msg = (struct cn_msg *)buffer;
    + msg = buffer_to_cn_msg(buffer);
    ev = (struct proc_event *)msg->data;
    memset(&ev->event_data, 0, sizeof(ev->event_data));
    get_seq(&msg->seq, &ev->cpu);
    ktime_get_ts(&ts); /* get high res monotonic timestamp */
    - put_unaligned(timespec_to_ns(&ts), (__u64 *)&ev->timestamp_ns);
    + ev->timestamp_ns = timespec_to_ns(&ts);
    ev->what = PROC_EVENT_SID;
    ev->event_data.sid.process_pid = task->pid;
    ev->event_data.sid.process_tgid = task->tgid;
    @@ -185,17 +197,17 @@ void proc_ptrace_connector(struct task_s
    struct cn_msg *msg;
    struct proc_event *ev;
    struct timespec ts;
    - __u8 buffer[CN_PROC_MSG_SIZE];
    + __u8 buffer[CN_PROC_MSG_SIZE] __aligned(8);

    if (atomic_read(&proc_event_num_listeners) < 1)
    return;

    - msg = (struct cn_msg *)buffer;
    + msg = buffer_to_cn_msg(buffer);
    ev = (struct proc_event *)msg->data;
    memset(&ev->event_data, 0, sizeof(ev->event_data));
    get_seq(&msg->seq, &ev->cpu);
    ktime_get_ts(&ts); /* get high res monotonic timestamp */
    - put_unaligned(timespec_to_ns(&ts), (__u64 *)&ev->timestamp_ns);
    + ev->timestamp_ns = timespec_to_ns(&ts);
    ev->what = PROC_EVENT_PTRACE;
    ev->event_data.ptrace.process_pid = task->pid;
    ev->event_data.ptrace.process_tgid = task->tgid;
    @@ -220,17 +232,17 @@ void proc_comm_connector(struct task_str
    struct cn_msg *msg;
    struct proc_event *ev;
    struct timespec ts;
    - __u8 buffer[CN_PROC_MSG_SIZE];
    + __u8 buffer[CN_PROC_MSG_SIZE] __aligned(8);

    if (atomic_read(&proc_event_num_listeners) < 1)
    return;

    - msg = (struct cn_msg *)buffer;
    + msg = buffer_to_cn_msg(buffer);
    ev = (struct proc_event *)msg->data;
    memset(&ev->event_data, 0, sizeof(ev->event_data));
    get_seq(&msg->seq, &ev->cpu);
    ktime_get_ts(&ts); /* get high res monotonic timestamp */
    - put_unaligned(timespec_to_ns(&ts), (__u64 *)&ev->timestamp_ns);
    + ev->timestamp_ns = timespec_to_ns(&ts);
    ev->what = PROC_EVENT_COMM;
    ev->event_data.comm.process_pid = task->pid;
    ev->event_data.comm.process_tgid = task->tgid;
    @@ -247,18 +259,18 @@ void proc_exit_connector(struct task_str
    {
    struct cn_msg *msg;
    struct proc_event *ev;
    - __u8 buffer[CN_PROC_MSG_SIZE];
    + __u8 buffer[CN_PROC_MSG_SIZE] __aligned(8);
    struct timespec ts;

    if (atomic_read(&proc_event_num_listeners) < 1)
    return;

    - msg = (struct cn_msg*)buffer;
    + msg = buffer_to_cn_msg(buffer);
    ev = (struct proc_event*)msg->data;
    memset(&ev->event_data, 0, sizeof(ev->event_data));
    get_seq(&msg->seq, &ev->cpu);
    ktime_get_ts(&ts); /* get high res monotonic timestamp */
    - put_unaligned(timespec_to_ns(&ts), (__u64 *)&ev->timestamp_ns);
    + ev->timestamp_ns = timespec_to_ns(&ts);
    ev->what = PROC_EVENT_EXIT;
    ev->event_data.exit.process_pid = task->pid;
    ev->event_data.exit.process_tgid = task->tgid;
    @@ -284,18 +296,18 @@ static void cn_proc_ack(int err, int rcv
    {
    struct cn_msg *msg;
    struct proc_event *ev;
    - __u8 buffer[CN_PROC_MSG_SIZE];
    + __u8 buffer[CN_PROC_MSG_SIZE] __aligned(8);
    struct timespec ts;

    if (atomic_read(&proc_event_num_listeners) < 1)
    return;

    - msg = (struct cn_msg*)buffer;
    + msg = buffer_to_cn_msg(buffer);
    ev = (struct proc_event*)msg->data;
    memset(&ev->event_data, 0, sizeof(ev->event_data));
    msg->seq = rcvd_seq;
    ktime_get_ts(&ts); /* get high res monotonic timestamp */
    - put_unaligned(timespec_to_ns(&ts), (__u64 *)&ev->timestamp_ns);
    + ev->timestamp_ns = timespec_to_ns(&ts);
    ev->cpu = -1;
    ev->what = PROC_EVENT_NONE;
    ev->event_data.ack.err = err;



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