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] Thanks for the review, --breno
