On Fri, May 13, 2022 at 2:11 PM Ashish Kalra <ashkalra@xxxxxxx> wrote: > > Hello Sean & Peter, > > On 5/13/22 14:49, Sean Christopherson wrote: > > 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. > > Yes, this function is also vulnerable as it allocates the return buffer > using kmalloc() and copies back to user the buffer sized as per the user > provided length (and not the FW returned length), so it surely needs fixup. > > I will update all these instances to use kzalloc() instead of kmalloc(). Do we need the alloc_page() in __sev_dbg_encrypt_user() to have __GFP_ZERO too? > > > 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() > > These functions are part of the ccp driver and a fix for them has > already been sent upstream to linux-crypto@xxxxxxxxxxxxxxx and > linux-kernel@xxxxxxxxxxxxxxx: > > [PATCH] crypto: ccp - Use kzalloc for sev ioctl interfaces to prevent > kernel memory leak > > Thanks, > > Ashish > > > > > 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;
