Re: [PATCH RFC v2] tpm: tpm_vtpm_proxy: do not reference kernel memory as user memory

[Stefan Berger]

On 5/31/23 13:17, Jarkko Sakkinen wrote:
> On Tue, 2023-05-30 at 13:45 -0400, Stefan Berger wrote:
> > On 5/29/23 22:01, Jarkko Sakkinen wrote:
> > > From: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxx>
> >
> > > -	rc = copy_to_user(buf, proxy_dev->buffer, len);
> > > +	if (buf)
> > > +		rc = copy_to_user(buf, proxy_dev->buffer, len);
> > > +
> >
> > Looking through other drivers it seems buf is always expected to be a valid non-NULL pointer on file_operations.read().
> >
> >
> > https://elixir.bootlin.com/linux/latest/source/arch/x86/mm/tlb.c#L1279   simple_read_from_buffer will pass the pointer to the user buffer along and it ('to') ends up in copy_to_user(to, ...);
> >
> >
> > Same here: https://elixir.bootlin.com/linux/latest/source/security/integrity/ima/ima_fs.c#L41
>
> It is good to mention here that IMA uses __user tagged pointers
> correctly, and it does not really compare to the vtpm driver code
> by any possible means. So let's not add illegit comparison points.

Yes, sir. Did you read David' response?
> BR, Jarkko