netdev - [RFC PATCH] net/smc: Consider using kfree_sensitive() to free cpu

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Message-Id: <20250411044456.1661380-1-zilin@seu.edu.cn>
Date: Fri, 11 Apr 2025 04:44:56 +0000
From: Zilin Guan <zilin@....edu.cn>
To: wenjia@...ux.ibm.com
Cc: jaka@...ux.ibm.com,
	alibuda@...ux.alibaba.com,
	tonylu@...ux.alibaba.com,
	guwen@...ux.alibaba.com,
	davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	horms@...nel.org,
	linux-rdma@...r.kernel.org,
	linux-s390@...r.kernel.org,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	jianhao.xu@....edu.cn,
	Zilin Guan <zilin@....edu.cn>
Subject: [RFC PATCH] net/smc: Consider using kfree_sensitive() to free cpu_addr

Hello,

In smcr_buf_unuse() and smc_buf_unuse(), memzero_explicit() is used to
clear cpu_addr when it is no longer in use, suggesting that cpu_addr
may contain sensitive information.

To ensure proper handling of this sensitive memory, I propose using
kfree_sensitive()/kvfree_sensitive instead of kfree()/vfree() to free
cpu_addr in both smcd_buf_free() and smc_buf_free(). This change aims
to prevent potential sensitive data leaks.

I am submitting this as an RFC to seek feedback on whether this change
is appropriate and aligns with the subsystem's expectations. If confirmed
to be useful, I will send a formal patch.

Signed-off-by: Zilin Guan <zilin@....edu.cn>
---
 net/smc/smc_core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c
index ac07b963aede..1b5eb0149b89 100644
--- a/net/smc/smc_core.c
+++ b/net/smc/smc_core.c
@@ -1388,7 +1388,7 @@ static void smcr_buf_free(struct smc_link_group *lgr, bool is_rmb,
 	if (!buf_desc->is_vm && buf_desc->pages)
 		__free_pages(buf_desc->pages, buf_desc->order);
 	else if (buf_desc->is_vm && buf_desc->cpu_addr)
-		vfree(buf_desc->cpu_addr);
+		kvfree_sensitive(buf_desc->cpu_addr, buf_desc->len);
 	kfree(buf_desc);
 }
 
@@ -1400,7 +1400,7 @@ static void smcd_buf_free(struct smc_link_group *lgr, bool is_dmb,
 		buf_desc->len += sizeof(struct smcd_cdc_msg);
 		smc_ism_unregister_dmb(lgr->smcd, buf_desc);
 	} else {
-		kfree(buf_desc->cpu_addr);
+		kfree_sensitive(buf_desc->cpu_addr);
 	}
 	kfree(buf_desc);
 }
-- 
2.34.1