Re: [PATCH 1/5] KVM: e500: retry if no memslot is found
From: Sean Christopherson <seanjc@google.com>
Date: 2025-01-09 19:00:03
Also in:
kvm, lkml, regressions, stable
On Thu, Jan 09, 2025, Paolo Bonzini wrote:
quoted hunk ↗ jump to hunk
Avoid a NULL pointer dereference if the memslot table changes between the exit and the call to kvmppc_e500_shadow_map(). Cc: stable@vger.kernel.org Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> --- arch/powerpc/kvm/e500_mmu_host.c | 5 +++++ 1 file changed, 5 insertions(+)diff --git a/arch/powerpc/kvm/e500_mmu_host.c b/arch/powerpc/kvm/e500_mmu_host.c index e5a145b578a4..732335444d68 100644 --- a/arch/powerpc/kvm/e500_mmu_host.c +++ b/arch/powerpc/kvm/e500_mmu_host.c@@ -349,6 +349,11 @@ static inline int kvmppc_e500_shadow_map(struct kvmppc_vcpu_e500 *vcpu_e500, * pointer through from the first lookup. */ slot = gfn_to_memslot(vcpu_e500->vcpu.kvm, gfn); + if (!slot) { + ret = -EAGAIN; + goto out; + }
This is unnecessary, __gfn_to_hva_many() checks for a NULL @slot.
static unsigned long __gfn_to_hva_many(const struct kvm_memory_slot *slot, gfn_t gfn,
gfn_t *nr_pages, bool write)
{
if (!slot || slot->flags & KVM_MEMSLOT_INVALID)
return KVM_HVA_ERR_BAD;
if (memslot_is_readonly(slot) && write)
return KVM_HVA_ERR_RO_BAD;
if (nr_pages)
*nr_pages = slot->npages - (gfn - slot->base_gfn);
return __gfn_to_hva_memslot(slot, gfn);
}
unsigned long gfn_to_hva_memslot(struct kvm_memory_slot *slot,
gfn_t gfn)
{
return gfn_to_hva_many(slot, gfn, NULL);
}
Not checking the return value and doing a VMA lookup on hva=-1 when tlbsel==1 is
gross, but it should be functionally safe.
Returning -EAGAIN is nicer (kvmppc_e500_shadow_map() will inevitably return -EINVAL),
but in practice it doesn't matter because all callers ultimately ignore the return
value.
Since there's a ratelimited printk that yells if there's no slot, it's probably
best to let sleeping dogs lie.
if (likely(!pfnmap)) {
tsize_pages = 1UL << (tsize + 10 - PAGE_SHIFT);
pfn = __kvm_faultin_pfn(slot, gfn, FOLL_WRITE, NULL, &page);
if (is_error_noslot_pfn(pfn)) {
if (printk_ratelimit())
pr_err("%s: real page not found for gfn %lx\n",
__func__, (long)gfn);
return -EINVAL;
}
+
hva = gfn_to_hva_memslot(slot, gfn);
if (tlbsel == 1) {
--
2.47.1