linux-kernel - Re: [PATCH] crypto: ccp - Fix crash when rebind ccp device for ccp.ko

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Message-ID: <d08e8494-851e-74b0-fdd8-ce2517dafc7a@amd.com>
Date: Mon, 23 Jun 2025 12:17:44 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: Mengbiao Xiong <xisme1998@...il.com>, herbert@...dor.apana.org.au,
 davem@...emloft.net
Cc: john.allen@....com, linux-crypto@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] crypto: ccp - Fix crash when rebind ccp device for ccp.ko

On 6/23/25 01:25, Mengbiao Xiong wrote:
> When CONFIG_CRYPTO_DEV_CCP_DEBUGFS is enabled, rebinding
> the ccp device causes the following crash:
> 
> $ echo '0000:0a:00.2' > /sys/bus/pci/drivers/ccp/unbind
> $ echo '0000:0a:00.2' > /sys/bus/pci/drivers/ccp/bind
> 
> [  204.976930] BUG: kernel NULL pointer dereference, address: 0000000000000098
> [  204.978026] #PF: supervisor write access in kernel mode
> [  204.979126] #PF: error_code(0x0002) - not-present page
> [  204.980226] PGD 0 P4D 0
> [  204.981317] Oops: Oops: 0002 [#1] SMP NOPTI
> ...
> [  204.997852] Call Trace:
> [  204.999074]  <TASK>
> [  205.000297]  start_creating+0x9f/0x1c0
> [  205.001533]  debugfs_create_dir+0x1f/0x170
> [  205.002769]  ? srso_return_thunk+0x5/0x5f
> [  205.004000]  ccp5_debugfs_setup+0x87/0x170 [ccp]
> [  205.005241]  ccp5_init+0x8b2/0x960 [ccp]
> [  205.006469]  ccp_dev_init+0xd4/0x150 [ccp]
> [  205.007709]  sp_init+0x5f/0x80 [ccp]
> [  205.008942]  sp_pci_probe+0x283/0x2e0 [ccp]
> [  205.010165]  ? srso_return_thunk+0x5/0x5f
> [  205.011376]  local_pci_probe+0x4f/0xb0
> [  205.012584]  pci_device_probe+0xdb/0x230
> [  205.013810]  really_probe+0xed/0x380
> [  205.015024]  __driver_probe_device+0x7e/0x160
> [  205.016240]  device_driver_attach+0x2f/0x60
> [  205.017457]  bind_store+0x7c/0xb0
> [  205.018663]  drv_attr_store+0x28/0x40
> [  205.019868]  sysfs_kf_write+0x5f/0x70
> [  205.021065]  kernfs_fop_write_iter+0x145/0x1d0
> [  205.022267]  vfs_write+0x308/0x440
> [  205.023453]  ksys_write+0x6d/0xe0
> [  205.024616]  __x64_sys_write+0x1e/0x30
> [  205.025778]  x64_sys_call+0x16ba/0x2150
> [  205.026942]  do_syscall_64+0x56/0x1e0
> [  205.028108]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
> [  205.029276] RIP: 0033:0x7fbc36f10104
> [  205.030420] Code: 89 02 48 c7 c0 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 8d 05 e1 08 2e 00 8b 00 85 c0 75 13 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 54 f3 c3 66 90 41 54 55 49 89 d4 53 48 89 f5
> 
> This patch sets ccp_debugfs_dir to NULL after destroying it in
> ccp5_debugfs_destroy, allowing the directory dentry to be
> recreated when rebinding the ccp device.
> 
> Tested on AMD Ryzen 7 1700X.
> 
> Fixes: 3cdbe346ed3f ("crypto: ccp - Add debugfs entries for CCP information")
> Signed-off-by: Mengbiao Xiong <xisme1998@...il.com>
> ---
>  drivers/crypto/ccp/ccp-debugfs.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/crypto/ccp/ccp-debugfs.c b/drivers/crypto/ccp/ccp-debugfs.c
> index a1055554b..0d432f3c4 100644
> --- a/drivers/crypto/ccp/ccp-debugfs.c
> +++ b/drivers/crypto/ccp/ccp-debugfs.c
> @@ -320,4 +320,5 @@ void ccp5_debugfs_setup(struct ccp_device *ccp)
>  void ccp5_debugfs_destroy(void)
>  {
>  	debugfs_remove_recursive(ccp_debugfs_dir);
> +	ccp_debugfs_dir = NULL;

Hmmm... it seems like this should be protected by the mutex similar to how
ccp5_debugfs_setup() is, right?

Maybe something like:

	mutex_lock(&ccp_debugfs_lock);
	if (ccp_debugfs_dir) {
		debugfs_remove_recursive(ccp_debugfs_dir);
		ccp_debugfs_dir = NULL;
	}
	mutex_unlock(&ccp_debugfs_lock);

That should also fix the issue, thoughts?

Thanks,
Tom

>  }