Re: [RFC v2 4/5] tpm: Increase TPM_BUFSIZE to 8kB for chunking support

[Jarkko Sakkinen]

On Sat, May 09, 2026 at 05:54:25PM +0300, Jarkko Sakkinen wrote:
> On Tue, Mar 24, 2026 at 11:42:43PM +0530, Arun Menon wrote:
> > The size of the command is checked against TPM_BUFSIZE early on before
> > even sending it to the backend. We therefore need to increase the
> > TPM_BUFSIZE to allow support for larger commands.
> > 
> > For now, 8KB seems sufficient for ML-KEM and ML-DSA algorithms and it is
> > also order-1 safe.
> > 
> > Signed-off-by: Arun Menon <armenon@xxxxxxxxxx>
> > ---
> >  drivers/char/tpm/tpm.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
> > index 87d68ddf270a7..26c3765fbd732 100644
> > --- a/drivers/char/tpm/tpm.h
> > +++ b/drivers/char/tpm/tpm.h
> > @@ -33,7 +33,7 @@
> >  #endif
> >  
> >  #define TPM_MINOR		224	/* officially assigned */
> > -#define TPM_BUFSIZE		4096
> > +#define TPM_BUFSIZE		8192
> >  #define TPM_NUM_DEVICES		65536
> >  #define TPM_RETRY		50
> >  
> > -- 
> > 2.53.0
> > 
> 
> Shouldn't this prepend previous patch?

Also did you remark that tpm_buf would also need changes as it is fixed
to PAGE_SIZE?

I've made a patch that essentially makes tpm_buf size variable as caller
does kzalloc:

https://lore.kernel.org/linux-integrity/20260125192526.782202-12-jarkko@xxxxxxxxxx/

I'd see this as pretty good long-term solution.

BR, Jarkko