On Sun, 2023-11-05 at 23:59 +0200, Jarkko Sakkinen wrote:
> On Thu, 2023-10-26 at 13:55 -0400, James Bottomley wrote:
> > On Thu, 2023-10-26 at 10:10 -0700, Jerry Snitselaar wrote:
> > > On Wed, Oct 25, 2023 at 08:35:55PM +0300, Jarkko Sakkinen wrote:
> > > > On Wed Oct 25, 2023 at 12:03 PM EEST, Jerry Snitselaar wrote:
> > > > > Reviewed-by: Jerry Snitselaar <jsnitsel@xxxxxxxxxx>
> > > >
> > > > On Wed, 2023-10-25 at 02:03 -0700, Jerry Snitselaar wrote:
> > > > > Reviewed-by: Jerry Snitselaar <jsnitsel@xxxxxxxxxx>
> > > > >
> > > >
> > > > Thanks I'll add it to the next round.
> > > >
> > > > For the tpm_buf_read(), I was thinking along the lines of:
> > > >
> > > > /**
> > > > * tpm_buf_read() - Read from a TPM buffer
> > > > * @buf: &tpm_buf instance
> > > > * @pos: position within the buffer
> > > > * @count: the number of bytes to read
> > > > * @output: the output buffer
> > > > *
> > > > * Read bytes from a TPM buffer, and update the position. Returns
> > > > false when the
> > > > * amount of bytes requested would overflow the buffer, which is
> > > > expected to
> > > > * only happen in the case of hardware failure.
> > > > */
> > > > static bool tpm_buf_read(const struct tpm_buf *buf, off_t *pos,
> > > > size_t count, void *output)
> > > > {
> > > > off_t next = *pos + count;
> > > >
> > > > if (next >= buf->length) {
> > > > pr_warn("%s: %lu >= %lu\n", __func__, next,
> > > > *offset);
> > > > return false;
> > > > }
> > > >
> > > > memcpy(output, &buf->data[*pos], count);
> > > > *offset = next;
> > > > return true;
> > > > }
> > > >
> > > > BR, Jarkko
> > > >
> > >
> > > Then the callers will check, and return -EIO?
> >
> > Really, no, why would we do that?
> >
> > The initial buffer is a page and no TPM currently can have a command
> > that big, so if the buffer overflows, it's likely a programming error
> > (failure to terminate loop or something) rather than a runtime one (a
> > user actually induced a command that big and wanted it to be sent to
> > the TPM). The only reason you might need to check is the no-alloc case
> > and you passed in a much smaller buffer, but even there, I would guess
> > it will come down to a coding fault not a possible runtime error.
>
>
> Yeah, this was my thinking too. So in HMAC case you anyway would not
> need to check it because crypto is destined to fail anyway.
>
> Returning boolean here does no harm so I thought that this is overally
> good compromise.
Or actually maybe we should go just with void, as it does have even
then "return value", as it emits to klog, right?
BR, Jarkko
