On Mon, Jun 27, 2022 at 12:10 PM Sean Christopherson <seanjc@xxxxxxxxxx> wrote: > > On Mon, Jun 27, 2022, Peter Gonda wrote: > > Clear to the @pages array pointer in sev_unpin_memory to avoid leaving a > > dangling pointer to invalid memory. > > > > Signed-off-by: Peter Gonda <pgonda@xxxxxxxxxx> > > Cc: Greg Thelen <gthelen@xxxxxxxxxx> > > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> > > Cc: Sean Christopherson <seanjc@xxxxxxxxxx> > > Cc: Tom Lendacky <thomas.lendacky@xxxxxxx> > > Cc: kvm@xxxxxxxxxxxxxxx > > Cc: linux-kernel@xxxxxxxxxxxxxxx > > --- > > arch/x86/kvm/svm/sev.c | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c > > index 309bcdb2f929..485ad86c01c6 100644 > > --- a/arch/x86/kvm/svm/sev.c > > +++ b/arch/x86/kvm/svm/sev.c > > @@ -452,6 +452,7 @@ static void sev_unpin_memory(struct kvm *kvm, struct page **pages, > > unpin_user_pages(pages, npages); > > kvfree(pages); > > sev->pages_locked -= npages; > > + *pages = NULL; > > Would this have helped detect a real bug? I generally like cleaning up, but this > leaves things in a somewhat inconsistent state, e.g. when unpinning a kvm_enc_region, > pages will be NULL but npages will be non-zero. It's somewhat moot because the > region is immediately freed in that case, but that begs the question of what real > benefit this provides. sev_dbg_crypt() is the only flow where there's much danger > of a use-after-free. > No strong opinion here, I just thought since this is a helper that takes a 'struct page **pages" we may as well clear this. While there are no bugs caught now if someone were to introduce something wrong this would make it more clear. We could update sev_unpin_memory() to take a int *npages so it can be cleared as well. Since kvm_enc_region describes a region with u64 instead of pointers that seemed "safer" give you'd have to cast them to dereference. Totally fine with the NACK of course. =]
