perf_counter: Add forward/backward attribute ABI compatibility

Provide for means of extending the perf_counter_attr in a 'natural' way.

We allow growing the structure by appending fields at the end by specifying
the full structure size inside it.

When a new kernel sees a smaller (old) structure, it will 0 pad the tail.
When an old kernel sees a larger (new) structure, it will verify the tail
consists of 0s, otherwise fail.

If we fail due to a size-mismatch, we return -E2BIG and write the kernel's
native attribe size back into the provided structure.

Furthermore, add some attribute verification, so that we'll fail counter
creation when unknown bits are present (PERF_SAMPLE, PERF_FORMAT, or in
the __reserved fields).

(This ABI detail is introduced while keeping the existing syscall ABI.)

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 86 insertions, 3 deletions

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 663bbe015057..29b685f551aa 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -3584,6 +3584,9 @@ perf_counter_alloc(struct perf_counter_attr *attr,
         case PERF_TYPE_TRACEPOINT:
                 pmu = tp_perf_counter_init(counter);
                 break;
+
+        default:
+                break;
         }
 done:
         err = 0;
@@ -3610,6 +3613,85 @@ done:
         return counter;
 }
 
+static int perf_copy_attr(struct perf_counter_attr __user *uattr,
+                          struct perf_counter_attr *attr)
+{
+        int ret;
+        u32 size;
+
+        if (!access_ok(VERIFY_WRITE, uattr, PERF_ATTR_SIZE_VER0))
+                return -EFAULT;
+
+        /*
+         * zero the full structure, so that a short copy will be nice.
+         */
+        memset(attr, 0, sizeof(*attr));
+
+        ret = get_user(size, &uattr->size);
+        if (ret)
+                return ret;
+
+        if (size > PAGE_SIZE)   /* silly large */
+                goto err_size;
+
+        if (!size)              /* abi compat */
+                size = PERF_ATTR_SIZE_VER0;
+
+        if (size < PERF_ATTR_SIZE_VER0)
+                goto err_size;
+
+        /*
+         * If we're handed a bigger struct than we know of,
+         * ensure all the unknown bits are 0.
+         */
+        if (size > sizeof(*attr)) {
+                unsigned long val;
+                unsigned long __user *addr;
+                unsigned long __user *end;
+
+                addr = PTR_ALIGN((void __user *)uattr + sizeof(*attr),
+                                sizeof(unsigned long));
+                end  = PTR_ALIGN((void __user *)uattr + size,
+                                sizeof(unsigned long));
+
+                for (; addr < end; addr += sizeof(unsigned long)) {
+                        ret = get_user(val, addr);
+                        if (ret)
+                                return ret;
+                        if (val)
+                                goto err_size;
+                }
+        }
+
+        ret = copy_from_user(attr, uattr, size);
+        if (ret)
+                return -EFAULT;
+
+        /*
+         * If the type exists, the corresponding creation will verify
+         * the attr->config.
+         */
+        if (attr->type >= PERF_TYPE_MAX)
+                return -EINVAL;
+
+        if (attr->__reserved_1 || attr->__reserved_2 || attr->__reserved_3)
+                return -EINVAL;
+
+        if (attr->sample_type & ~(PERF_SAMPLE_MAX-1))
+                return -EINVAL;
+
+        if (attr->read_format & ~(PERF_FORMAT_MAX-1))
+                return -EINVAL;
+
+out:
+        return ret;
+
+err_size:
+        put_user(sizeof(*attr), &uattr->size);
+        ret = -E2BIG;
+        goto out;
+}
+
 /**
  * sys_perf_counter_open - open a performance counter, associate it to a task/cpu
  *
@@ -3619,7 +3701,7 @@ done:
  * @group_fd:           group leader counter fd
  */
 SYSCALL_DEFINE5(perf_counter_open,
-                const struct perf_counter_attr __user *, attr_uptr,
+                struct perf_counter_attr __user *, attr_uptr,
                 pid_t, pid, int, cpu, int, group_fd, unsigned long, flags)
 {
         struct perf_counter *counter, *group_leader;
@@ -3635,8 +3717,9 @@ SYSCALL_DEFINE5(perf_counter_open,
         if (flags)
                 return -EINVAL;
 
-        if (copy_from_user(&attr, attr_uptr, sizeof(attr)) != 0)
-                return -EFAULT;
+        ret = perf_copy_attr(attr_uptr, &attr);
+        if (ret)
+                return ret;
 
         if (!attr.exclude_kernel) {
                 if (perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))