perf: Handle compat ioctl

When running a 32-bit userspace on a 64-bit kernel (eg. i386
application on x86_64 kernel or 32-bit arm userspace on arm64
kernel) some of the perf ioctls must be treated with special
care, as they have a pointer size encoded in the command.

For example, PERF_EVENT_IOC_ID in 32-bit world will be encoded
as 0x80042407, but 64-bit kernel will expect 0x80082407. In
result the ioctl will fail returning -ENOTTY.

This patch solves the problem by adding code fixing up the
size as compat_ioctl file operation.

Reported-by: Drew Richardson <drew.richardson@arm.com>
Signed-off-by: Pawel Moll <pawel.moll@arm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/1402671812-9078-1-git-send-email-pawel.moll@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 22 insertions, 1 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 1cf24b3e42ec..f9c1ed002dbc 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -41,6 +41,7 @@
 #include <linux/cgroup.h>
 #include <linux/module.h>
 #include <linux/mman.h>
+#include <linux/compat.h>
 
 #include "internal.h"
 
@@ -3717,6 +3718,26 @@ static long perf_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
         return 0;
 }
 
+#ifdef CONFIG_COMPAT
+static long perf_compat_ioctl(struct file *file, unsigned int cmd,
+                                unsigned long arg)
+{
+        switch (_IOC_NR(cmd)) {
+        case _IOC_NR(PERF_EVENT_IOC_SET_FILTER):
+        case _IOC_NR(PERF_EVENT_IOC_ID):
+                /* Fix up pointer size (usually 4 -> 8 in 32-on-64-bit case */
+                if (_IOC_SIZE(cmd) == sizeof(compat_uptr_t)) {
+                        cmd &= ~IOCSIZE_MASK;
+                        cmd |= sizeof(void *) << IOCSIZE_SHIFT;
+                }
+                break;
+        }
+        return perf_ioctl(file, cmd, arg);
+}
+#else
+# define perf_compat_ioctl NULL
+#endif
+
 int perf_event_task_enable(void)
 {
         struct perf_event *event;
@@ -4222,7 +4243,7 @@ static const struct file_operations perf_fops = {
         .read                   = perf_read,
         .poll                   = perf_poll,
         .unlocked_ioctl         = perf_ioctl,
-        .compat_ioctl           = perf_ioctl,
+        .compat_ioctl           = perf_compat_ioctl,
         .mmap                   = perf_mmap,
         .fasync                 = perf_fasync,
 };