[RFC PATCH -rc] gcov: Protect from uninitialized number of functions provided by GCC

[Leon Romanovsky <leon@kernel.org>]

From: Leon Romanovsky <leonro@nvidia.com>

The kernel compiled with GCC 10.2.1 and KASAN together with GCOV enabled
produces the following splats while reloading modules.

First splat [1] is generated due to the situation that gcov_info can be both
user and kernel pointer, the memcpy() during kmemdup() causes to this.
As a possible solution copy fields manually.

Second splat [2] is seen because n_function provided by GCC through
__gcov_init() is ridiculously high, in my case it was 2698213824.
IMHO it means that this field is not initialized, but I'm not sure.

[1]
 ==================================================================
 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
 gcov: could not save data for '/home/leonro/src/kernel/drivers/infiniband/hw/mlx5/std_types.gcda' (out o
f memory)

[2]
Colin has similar error [3].

 ------------[ cut here ]------------
 WARNING: CPU: 0 PID: 296 at mm/page_alloc.c:4859 __alloc_pages_nodemask+0x670/0x3190
 Modules linked in: mlx5_ib(-) mlx5_core mlxfw ptp ib_ipoib pps_core rdma_ucm rdma_cm iw_cm ib_cm ib_umad  ib_uverbs ib_core
 CPU: 0 PID: 296 Comm: modprobe Tainted: G    B             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
 RIP: 0010:__alloc_pages_nodemask+0x670/0x3190
 Code: e9 af fc ff ff 48 83 05 fd 28 90 05 01 81 e7 00 20 00 00 48 c7 44 24 28 00 00 00 00 0f 85 fb fd ff  ff 48 83 05 f0 28 90 05 01 <0f> 0b 48 83 05 ee 28 90 05 01 48 83 05 ee 28 90 05 01 e9 dc fd ff
 RSP: 0018:ffff88805f7ffa28 EFLAGS: 00010202
 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 1ffff1100befff5e
 RDX: 0000000000000000 RSI: 0000000000000017 RDI: 0000000000000000
 RBP: 000000050695a900 R08: ffff888060fc7900 R09: ffff888060fc793b
 R10: ffffed100c1f8f27 R11: ffffed100c1f8f28 R12: 0000000000040dc0
 R13: 000000050695a900 R14: 0000000000000017 R15: 0000000000000001
 FS:  00007f521f695740(0000) GS:ffff88806ce00000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 00007f31b013f000 CR3: 000000006637e001 CR4: 0000000000370eb0
 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
 Call Trace:
  ? __kmalloc_track_caller+0x17a/0x570
  ? gcov_info_dup+0xfe/0x730
  ? gcov_event+0x88d/0xd30
  ? gcov_module_notifier+0xe9/0x100
  ? blocking_notifier_call_chain+0x75/0xc0
  ? __x64_sys_delete_module+0x326/0x5a0
  ? entry_SYSCALL_64_after_hwframe+0x44/0xa9
  ? mark_lock+0xba0/0xba0
  ? mark_lock+0xba0/0xba0
  ? notifier_call_chain+0xeb/0x170
  ? blocking_notifier_call_chain+0x75/0xc0
  ? __x64_sys_delete_module+0x326/0x5a0
  ? do_syscall_64+0x45/0x70
  ? entry_SYSCALL_64_after_hwframe+0x44/0xa9
  ? warn_alloc+0x130/0x130
  ? lock_acquire+0x1f2/0xa30
  ? fs_reclaim_acquire+0x1f/0x70
  ? fs_reclaim_release+0x1f/0x50
  ? __kasan_check_read+0x1d/0x30
  ? reacquire_held_locks+0x420/0x420
  ? reacquire_held_locks+0x420/0x420
  kmalloc_order+0x3f/0xc0
  kmalloc_order_trace+0x24/0x220
  __kmalloc+0x41b/0x5a0
  ? gcov_info_dup+0xfe/0x730
  ? memcpy+0x73/0xa0
  gcov_info_dup+0x176/0x730
  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
 RIP: 0033:0x7f521f7c531b
 Code: 73 01 c3 48 8b 0d 7d 0b 0c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa b8 b0 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 4d 0b 0c 00 f7 d8 64 89 01 48
 RSP: 002b:00007ffe1bd4af48 EFLAGS: 00000206 ORIG_RAX: 00000000000000b0
 RAX: ffffffffffffffda RBX: 0000561a3eae0910 RCX: 00007f521f7c531b
 RDX: 0000000000000000 RSI: 0000000000000800 RDI: 0000561a3eae0978
 RBP: 0000561a3eae0910 R08: 1999999999999999 R09: 0000000000000000
 R10: 00007f521f839ac0 R11: 0000000000000206 R12: 0000000000000000
 R13: 0000561a3eae0978 R14: 0000000000000000 R15: 0000561a3eae84d0
 irq event stamp: 326464
 hardirqs last  enabled at (326463): [<ffffffff832ecdde>] _raw_spin_unlock_irqrestore+0x8e/0xb0
 hardirqs last disabled at (326464): [<ffffffff832ec994>] _raw_spin_lock_irqsave+0x34/0xa0
 hardirqs last disabled at (326464): [<ffffffff832ec994>] _raw_spin_lock_irqsave+0x34/0xa0
 softirqs last  enabled at (320794): [<ffffffff83600931>] __do_softirq+0x931/0xbc4
 softirqs last disabled at (320789): [<ffffffff83400f2f>] asm_call_on_stack+0xf/0x20
 ---[ end trace 065ea9cc2ba144a6 ]---

[3] https://bugzilla.kernel.org/show_bug.cgi?id=208885#c1
Cc: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
I have a strong feeling that this solution is not correct, but don't
know how to do it right. The problem exists and reproducable in seconds.
---
 kernel/gcov/gcc_4_7.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/kernel/gcov/gcc_4_7.c b/kernel/gcov/gcc_4_7.c
index 908fdf5098c3..357ef839cdd3 100644
--- a/kernel/gcov/gcc_4_7.c
+++ b/kernel/gcov/gcc_4_7.c
@@ -275,20 +275,23 @@ 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;
+	dup->version = info->version;
+	dup->stamp = info->stamp;
+	for (fi_idx = 0; i < GCOV_COUNTERS; i++)
+		dup->merge[i] = info->merge[i];
+	dup->n_functions = info->n_functions;

-	dup->filename = kstrdup(info->filename, GFP_KERNEL);
+	dup->filename = kstrdup_const(info->filename, GFP_KERNEL);
 	if (!dup->filename)
 		goto err_free;

-	dup->functions = kcalloc(info->n_functions,
-				 sizeof(struct gcov_fn_info *), GFP_KERNEL);
+	dup->functions =
+		kcalloc(info->n_functions, sizeof(struct gcov_fn_info *),
+			GFP_KERNEL | __GFP_NOWARN);
 	if (!dup->functions)
 		goto err_free;

@@ -359,7 +362,7 @@ void gcov_info_free(struct gcov_info *info)

 free_info:
 	kfree(info->functions);
-	kfree(info->filename);
+	kfree_const(info->filename);
 	kfree(info);
 }

--
2.26.2