Re: [kbuild-all] Re: [PATCH v43 01/15] Linux Random Number Generator

Chen, Rong A [off-list ref] wrote:

On 11/22/2021 7:47 PM, Stephan Mueller wrote:

quoted

Thanks for the notification.

I think this is a false-positive discussed before. __latent_entropy is
seemingly allowed for an entire linear buffer as seen in the declaration of
the variable input_pool_data in driver/char/random.c which is an array of u32.

The struct chacha20_state is a linear buffer of u32 words.

struct chacha20_block {
         u32 constants[4];
         union {
                 u32 u[CHACHA_KEY_SIZE_WORDS];
                 u8  b[CHACHA_KEY_SIZE];
         } key;
         u32 counter;
         u32 nonce[3];
};

Therefore it should be identical to the aforementioned example.

No. It is a struct & there's no guarantee all compilers will lay
it out as you  expect. There might even be a gap in the layout
since nonce[] has an odd number of elements.

quoted

The __latent_entropy marker therefore seems to be appropriate for this structure.

First, this is completely unnecessary since the input pool is marked for
latent entropy & changes there will affect the chacha context.

Also, if I'm reading the docs right, the __latent_entropy attribute
on a data structure only gets it initialised somewhat randomly.
If you want a continuous effect at runtime, then you need to
make the code mix the latent_entropy global variable into the
data structure.