Re: [PATCH] virtio-console: avoid DMA from vmalloc area
From: Xianting Tian
Date: Tue Jul 27 2021 - 22:58:47 EST
Arnd, thanks for your quick reply,
As we know put_chars() of virtio-console is registered to hvc framework.
I go throughed the code, actually there are totally three places that
put_chars() is called in hvc driver, but only 1 has issue which is
fixed by commit c4baad5029.
So I think the scenario that the buf is from "ioremap(), kmap_atomic() ,
fixmap, loadable module" doesn't exist for virtio-console.
If there is something wrong about above description, please correct me,
thanks.
Three places that put_chars() is called in hvc driver:
1, it is on stack buf, it is not ok for dma
hvc_console_print():
char c[N_OUTBUF] __ALIGNED__;
cons_ops[index]->put_chars(vtermnos[index], c, i);
2, just one byte, no issue for dma
static void hvc_poll_put_char(struct tty_driver *driver, int line,
char ch)
{
struct tty_struct *tty = driver->ttys[0];
struct hvc_struct *hp = tty->driver_data;
int n;
do {
n = hp->ops->put_chars(hp->vtermno, &ch, 1);
} while (n <= 0);
}
3, hp->outbuf is allocated in hvc_alloc() via kzalloc(), no issue for dma
static int hvc_push(struct hvc_struct *hp)
{
int n;
n = hp->ops->put_chars(hp->vtermno, hp->outbuf, hp->n_outbuf);
…
}
在 2021/7/27 下午9:18, Arnd Bergmann 写道:
On Tue, Jul 27, 2021 at 3:13 PM Xianting Tian
<xianting.tian@xxxxxxxxxxxxxxxxx> wrote:
@@ -1127,13 +1128,18 @@ static int put_chars(u32 vtermno, const char *buf, int count)
if (!port)
return -EPIPE;
- data = kmemdup(buf, count, GFP_ATOMIC);
- if (!data)
- return -ENOMEM;
+ if (is_vmalloc_addr(buf)) {
+ data = kmemdup(buf, count, GFP_ATOMIC);
What about buffers in .data? If those are in a loadable module, I guess you have
the same problem as with vmalloc() and vmap().
is_vmalloc_or_module_addr() would take care of both, not sure if there are
other examples that don't work. In theory it could be ioremap(), kmap_atomic()
or fixmap as well, but those seem less likely to matter here.
Arnd