Hi Andy,
On 2016/10/18 1:06, Andy Lutomirski wrote:
> hw_random carefully avoids using a stack buffer except in
> add_early_randomness(). This causes a crash in virtio_rng if
> CONFIG_VMAP_STACK=y.
I try to understand this patch, but I do not know why it will cause
a crash in virtio_rng with CONFIG_VMAP_STACK=y?
Could you please give me more info. about it.
Really thanks for that!
Yisheng Xie.
>
> Reported-by: Matt Mullins <mmullins@xxxxxxx>
> Tested-by: Matt Mullins <mmullins@xxxxxxx>
> Fixes: d3cc7996473a ("hwrng: fetch randomness only after device init")
> Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
> ---
>
> This fixes a crash in 4.9-rc1.
>
> resending because I typoed the git send-email command. I stealthily added
> Matt's Tested-by, too.
>
> drivers/char/hw_random/core.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
> index 9203f2d130c0..340f96e44642 100644
> --- a/drivers/char/hw_random/core.c
> +++ b/drivers/char/hw_random/core.c
> @@ -84,14 +84,14 @@ static size_t rng_buffer_size(void)
>
> static void add_early_randomness(struct hwrng *rng)
> {
> - unsigned char bytes[16];
> int bytes_read;
> + size_t size = min_t(size_t, 16, rng_buffer_size());
>
> mutex_lock(&reading_mutex);
> - bytes_read = rng_get_data(rng, bytes, sizeof(bytes), 1);
> + bytes_read = rng_get_data(rng, rng_buffer, size, 1);
> mutex_unlock(&reading_mutex);
> if (bytes_read > 0)
> - add_device_randomness(bytes, bytes_read);
> + add_device_randomness(rng_buffer, bytes_read);
> }
>
> static inline void cleanup_rng(struct kref *kref)
>
