On Sat, May 30, 2026 at 01:58:14AM +0300, Jarkko Sakkinen wrote: > On Tue, May 26, 2026 at 07:20:31PM +0100, Breno Leitao wrote: > > Hello Jarkko, > > > > On Mon, May 25, 2026 at 02:24:38AM +0000, Jarkko Sakkinen wrote: > > > On Sun, May 24, 2026 at 10:01:17AM -0400, Breno Leitao wrote: > > > > tpm_buf_append() guards against overflow of the underlying buffer by > > > > comparing the running length against PAGE_SIZE. Every other site in the > > > > TPM core uses TPM_BUFSIZE (4096) as the protocol-level cap on TPM > > > > command and response sizes. > > > > > > > > On 4K-page kernels PAGE_SIZE == TPM_BUFSIZE, so the two caps coincide > > > > and the inconsistency is invisible. On kernels with a larger base page > > > > size, e.g. CONFIG_ARM64_64K_PAGES=y or 16K pages, PAGE_SIZE exceeds > > > > TPM_BUFSIZE. > > > > > > > > This is a latent bug rather than user-visible bug, given most of the > > > > cases PAGE_SIZE = 4096. The mismatch is still worth fixing because > > > > future callers (e.g. the proposed TPM_BUFSIZE increase to 8 KiB, and the > > > > Secure Launch tpm_buf rework) rely on the overflow flag being > > > > authoritative. > > > > > > > > Use TPM_BUFSIZE instead of PAGE_SIZE so the append-time check > > > > matches the transmit-time cap on every page size. > > > > > > > > Signed-off-by: Breno Leitao <[email protected]> > > > > Fixes: a74f8b36352e ("tpm: introduce tpm_buf") > > > > --- > > > > > > There is no bug w/o a sympton of some sort. Not sure what the problem is > > > here. > > > > Sorry, there is no current problem in here, but there is inconsistency. > > > > There isn't a real problem today, just an inconsistency and what I > > called a latent bug, let me justify myself. > > > > Everywhere else in the TPM core uses TPM_BUFSIZE as the protocol cap, > > but this particular site uses PAGE_SIZE instead. Since PAGE_SIZE >= > > TPM_BUFSIZE, it doesn't cause any issue at the moment. > > > > That said, I still think the change is worthwhile for two reasons: > > > > 1. Consistency with the rest of the TPM core. > > 2. Decoupling TPM_BUFSIZE from PAGE_SIZE, so that if TPM_BUFSIZE ever > > grows beyond PAGE_SIZE[1], this code won't silently break. That's what I > > was referring to as a "latent bug" — though admittedly that phrasing > > was probably too strong. > > > > Link: > > https://lore.kernel.org/all/[email protected]/ [1] > > IMHO, if that is required for buffer chunking patch set, Arun > should pick it up a precursory patch but as far as mainline is > concerned right now, it is not broken. > > I'm somewhat resistant to any pure cleanup patches given how > things are right now in the world, *unless* they are part of > some relevant patch set as precursory patches.
That is fair, thanks for the heads-up! --breno
