On Fri, May 13, 2022, Peter Gonda wrote: > On Thu, May 12, 2022 at 4:23 PM Ashish Kalra <Ashish.Kalra@xxxxxxx> wrote: > > > > From: Ashish Kalra <ashish.kalra@xxxxxxx> > > > > For some sev ioctl interfaces, the length parameter that is passed maybe > > less than or equal to SEV_FW_BLOB_MAX_SIZE, but larger than the data > > that PSP firmware returns. In this case, kmalloc will allocate memory > > that is the size of the input rather than the size of the data. > > Since PSP firmware doesn't fully overwrite the allocated buffer, these > > sev ioctl interface may return uninitialized kernel slab memory. > > > > Reported-by: Andy Nguyen <theflow@xxxxxxxxxx> > > Suggested-by: David Rientjes <rientjes@xxxxxxxxxx> > > Suggested-by: Peter Gonda <pgonda@xxxxxxxxxx> > > Cc: kvm@xxxxxxxxxxxxxxx > > Cc: linux-kernel@xxxxxxxxxxxxxxx > > Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx> > > --- > > arch/x86/kvm/svm/sev.c | 6 +++--- > > 1 file changed, 3 insertions(+), 3 deletions(-) > > > > Can we just update all the kmalloc()s that buffers get given to the > PSP? For instance doesn't sev_send_update_data() have an issue? > Reading the PSP spec it seems like a user can call this ioctl with a > large hdr_len and the PSP will only fill out what's actually required > like in these fixed up cases? This is assuming the PSP is written to > spec (and just the current version). I'd rather have all of these > instances updated. Agreed, the kernel should explicitly initialize any copy_to_user() to source and never rely on the PSP to fill the entire blob unless there's an ironclad guarantee the entire struct/blob will be written. E.g. it's probably ok to skip zeroing "data" in sev_ioctl_do_platform_status(), but even then it might be wortwhile as defense-in-depth. Looking through other copy_to_user() calls: - "blob" in sev_ioctl_do_pek_csr() - "id_blob" in sev_ioctl_do_get_id2() - "pdh_blob" and "cert_blob" in sev_ioctl_do_pdh_export() The last one is probably fine since the copy length comes from the PSP, but it's not like these ioctls are performance critical... /* If we query the length, FW responded with expected data. */ input.cert_chain_len = data.cert_chain_len; input.pdh_cert_len = data.pdh_cert_len;
