From: Gleb Natapov <gleb@redhat.com>
To: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Andy Honig <ahonig@google.com>, kvm <kvm@vger.kernel.org>
Subject: Re: KVM: x86: drop alignment checks from KVM_MSR_SYSTEM_TIME address
Date: Fri, 22 Mar 2013 23:57:08 +0200 [thread overview]
Message-ID: <20130322215708.GB9382@redhat.com> (raw)
In-Reply-To: <20130322211947.GA2685@amt.cnet>
On Fri, Mar 22, 2013 at 06:19:47PM -0300, Marcelo Tosatti wrote:
>
> The alignment check is not necessary given that "KVM: x86: Convert
> MSR_KVM_SYSTEM_TIME to use gfn_to_hva_cache" (0b79459b482e85cb742)
> uses kvm_write_guest which is able to handle data across page
> properly.
>
It uses kvm_write_guest_cached which calls to copy_to_user() directly.
While this will not allow to overwrite page that does not belong to qemu
process, it is possible to write outside of memory slot. May be we
should use kvm_write_guest to do system time updates.
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index f19ac0a..ec830fa 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1952,10 +1952,6 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>
> gpa_offset = data & ~(PAGE_MASK | 1);
>
> - /* Check that the address is 32-byte aligned. */
> - if (gpa_offset & (sizeof(struct pvclock_vcpu_time_info) - 1))
> - break;
> -
> if (kvm_gfn_to_hva_cache_init(vcpu->kvm,
> &vcpu->arch.pv_time, data & ~1ULL))
> vcpu->arch.pv_time_enabled = false;
--
Gleb.
next prev parent reply other threads:[~2013-03-22 21:57 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-03-22 19:14 KVM: x86: relax MSR_KVM_SYSTEM_TIME alignment check Marcelo Tosatti
2013-03-22 19:21 ` Gleb Natapov
2013-03-22 19:47 ` Marcelo Tosatti
2013-03-22 21:19 ` KVM: x86: drop alignment checks from KVM_MSR_SYSTEM_TIME address Marcelo Tosatti
2013-03-22 21:57 ` Gleb Natapov [this message]
2013-03-23 0:17 ` Andrew Honig
2013-03-23 14:12 ` Gleb Natapov
2013-04-11 16:05 ` Marcelo Tosatti
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