From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Date: Wed, 03 Sep 2014 08:34:27 +0000 Subject: Re: [PATCH] powerpc/kvm/cma: Fix panic introduces by signed shift operation Message-Id: <5406D293.3060404@redhat.com> List-Id: References: <1409674381-29465-1-git-send-email-ldufour@linux.vnet.ibm.com> In-Reply-To: <1409674381-29465-1-git-send-email-ldufour@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Laurent Dufour , linuxppc-dev@lists.ozlabs.org Cc: kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, linux-kernel@vger.kernel.org, Alexey Kardashevskiy , Paul Mackerras , Alexander Graf , "Aneesh Kumar K.V" , Joonsoo Kim , Benjamin Herrenschmidt Il 02/09/2014 18:13, Laurent Dufour ha scritto: > fc95ca7284bc54953165cba76c3228bd2cdb9591 introduces a memset in > kvmppc_alloc_hpt since the general CMA doesn't clear the memory it > allocates. > > However, the size argument passed to memset is computed from a signed value > and its signed bit is extended by the cast the compiler is doing. This lead > to extremely large size value when dealing with order value >= 31, and > almost all the memory following the allocated space is cleaned. As a > consequence, the system is panicing and may even fail spawning the kdump > kernel. > > This fix makes use of an unsigned value for the memset's size argument to > avoid sign extension. Among this fix, another shift operation which may > lead to signed extended value too is also fixed. > > Cc: Alexey Kardashevskiy > Cc: Paul Mackerras > Cc: Alexander Graf > Cc: Aneesh Kumar K.V > Cc: Joonsoo Kim > Cc: Benjamin Herrenschmidt > Signed-off-by: Laurent Dufour > --- > arch/powerpc/kvm/book3s_64_mmu_hv.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c > index 72c20bb16d26..79294c4c5015 100644 > --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c > +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c > @@ -62,10 +62,10 @@ long kvmppc_alloc_hpt(struct kvm *kvm, u32 *htab_orderp) > } > > kvm->arch.hpt_cma_alloc = 0; > - page = kvm_alloc_hpt(1 << (order - PAGE_SHIFT)); > + page = kvm_alloc_hpt(1ul << (order - PAGE_SHIFT)); > if (page) { > hpt = (unsigned long)pfn_to_kaddr(page_to_pfn(page)); > - memset((void *)hpt, 0, (1 << order)); > + memset((void *)hpt, 0, (1ul << order)); > kvm->arch.hpt_cma_alloc = 1; > } > > Thanks, applied to kvm/master. Paolo