Re: [RFC PATCH] net/smc: Consider using kfree_sensitive() to free cpu_addr

[Andrew Lunn]

On Fri, Apr 11, 2025 at 04:44:56AM +0000, Zilin Guan wrote:
> 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.

There is another possible meaning:

			memzero_explicit(conn->sndbuf_desc->cpu_addr, bufsize);
			WRITE_ONCE(conn->sndbuf_desc->used, 0);

The WRITE_ONCE() probably tells the hardware the buffer is ready for
it. In order to ensure they memzero has completed and that the
compiler does not reorder the instructions you need a memory barrier:

static inline void memzero_explicit(void *s, size_t count)
{
	memset(s, 0, count);
	barrier_data(s);
}

So it could be using memzero_explicit() just for the barrier_data().

Please spend some time to analyze this code, look at the git history
etc, see if there are any clues as to why memzero_explicit is used, or
if there is any indication of sensitive information.

	Andrew