[PATCH rdma-next 1/4] gcov: Open-code kmemdup() to work correctly with kernel and user space pointers

[Leon Romanovsky <leon@kernel.org>]

From: Leon Romanovsky <leonro@nvidia.com>

The kernel with KASAN and GCOV enabled generates the following splat
due to the situation that gcov_info can be both user and kernel pointer.

It is triggered by the memcpy() inside kmemdup(), so as a possible solution
let's copy fields manually.

 ==================================================================
 BUG: KASAN: global-out-of-bounds in kmemdup+0x43/0x70
 Read of size 120 at addr ffffffffa0d2c780 by task modprobe/296

 CPU: 0 PID: 296 Comm: modprobe Not tainted 5.9.0-rc1+ #1860
 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04 /01/2014
 Call Trace:
   dump_stack+0x128/0x1af
   print_address_description.constprop.0+0x2c/0x3f0
   _raw_spin_lock_irqsave+0x34/0xa0
   __kasan_check_read+0x1d/0x30
   kmemdup+0x43/0x70
   kmemdup+0x43/0x70
   gcov_info_dup+0x2d/0x730
   __kasan_check_write+0x20/0x30
   __mutex_unlock_slowpath+0x10d/0x740
   gcov_event+0x88d/0xd30
   gcov_module_notifier+0xe9/0x100
   notifier_call_chain+0xeb/0x170
   blocking_notifier_call_chain+0x75/0xc0
   __x64_sys_delete_module+0x326/0x5a0
   do_init_module+0x810/0x810
   syscall_enter_from_user_mode+0x40/0x420
   trace_hardirqs_on+0x45/0xb0
   syscall_enter_from_user_mode+0x40/0x420
   do_syscall_64+0x45/0x70
   entry_SYSCALL_64_after_hwframe+0x44/0xa9

 The buggy address belongs to the variable:
  __gcov_.uverbs_attr_get_obj+0x60/0xfffffffffff778e0 [mlx5_ib]

 Memory state around the buggy address:
  ffffffffa0d2c680: 00 f9 f9 f9 f9 f9 f9 f9 00 00 00 00 00 f9 f9 f9
  ffffffffa0d2c700: f9 f9 f9 f9 00 00 00 00 00 f9 f9 f9 f9 f9 f9 f9
 >ffffffffa0d2c780: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 f9 f9
                                                              ^
  ffffffffa0d2c800: f9 f9 f9 f9 00 00 00 00 00 f9 f9 f9 f9 f9 f9 f9
  ffffffffa0d2c880: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ==================================================================
 Disabling lock debugging due to kernel taint
 ---[ end trace 065ea9cc2ba144a6 ]---

Cc: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
 kernel/gcov/gcc_4_7.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/gcov/gcc_4_7.c b/kernel/gcov/gcc_4_7.c
index 908fdf5098c3..6d706c5eed5c 100644
--- a/kernel/gcov/gcc_4_7.c
+++ b/kernel/gcov/gcc_4_7.c
@@ -275,13 +275,13 @@ struct gcov_info *gcov_info_dup(struct gcov_info *info)
 	size_t fi_size; /* function info size */
 	size_t cv_size; /* counter values size */

-	dup = kmemdup(info, sizeof(*dup), GFP_KERNEL);
+	dup = kzalloc(sizeof(*dup), GFP_KERNEL);
 	if (!dup)
 		return NULL;

-	dup->next = NULL;
-	dup->filename = NULL;
-	dup->functions = NULL;
+	for (fi_idx = 0; fi_idx < GCOV_COUNTERS; fi_idx++)
+		dup->merge[fi_idx] = info->merge[fi_idx];
+	dup->n_functions = info->n_functions;

 	dup->filename = kstrdup(info->filename, GFP_KERNEL);
 	if (!dup->filename)
--
2.26.2