* [PATCH] KVM: x86: do not pass poisoned hva to __kvm_set_memory_region
@ 2020-06-11 18:01 Paolo Bonzini
2020-06-11 20:14 ` Maxim Levitsky
0 siblings, 1 reply; 2+ messages in thread
From: Paolo Bonzini @ 2020-06-11 18:01 UTC (permalink / raw)
To: linux-kernel, kvm; +Cc: Maxim Levitsky
__kvm_set_memory_region does not use the hva at all, so trying to
catch use-after-delete is pointless and, worse, it fails access_ok
now that we apply it to all memslots including private kernel ones.
This fixes an AVIC regression.
Fixes: 09d952c971a5 ("KVM: check userspace_addr for all memslots", 2020-06-01)
Reported-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/x86.c | 7 +------
1 file changed, 1 insertion(+), 6 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 290784ba63e4..00c88c2f34e4 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9951,13 +9951,8 @@ int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size)
if (!slot || !slot->npages)
return 0;
- /*
- * Stuff a non-canonical value to catch use-after-delete. This
- * ends up being 0 on 32-bit KVM, but there's no better
- * alternative.
- */
- hva = (unsigned long)(0xdeadull << 48);
old_npages = slot->npages;
+ hva = 0;
}
for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
--
2.26.2
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] KVM: x86: do not pass poisoned hva to __kvm_set_memory_region
2020-06-11 18:01 [PATCH] KVM: x86: do not pass poisoned hva to __kvm_set_memory_region Paolo Bonzini
@ 2020-06-11 20:14 ` Maxim Levitsky
0 siblings, 0 replies; 2+ messages in thread
From: Maxim Levitsky @ 2020-06-11 20:14 UTC (permalink / raw)
To: Paolo Bonzini, linux-kernel, kvm
On Thu, 2020-06-11 at 14:01 -0400, Paolo Bonzini wrote:
> __kvm_set_memory_region does not use the hva at all, so trying to
> catch use-after-delete is pointless and, worse, it fails access_ok
> now that we apply it to all memslots including private kernel ones.
> This fixes an AVIC regression.
>
> Fixes: 09d952c971a5 ("KVM: check userspace_addr for all memslots", 2020-06-01)
> Reported-by: Maxim Levitsky <mlevitsk@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> arch/x86/kvm/x86.c | 7 +------
> 1 file changed, 1 insertion(+), 6 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 290784ba63e4..00c88c2f34e4 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9951,13 +9951,8 @@ int __x86_set_memory_region(struct kvm *kvm, int id, gpa_t gpa, u32 size)
> if (!slot || !slot->npages)
> return 0;
>
> - /*
> - * Stuff a non-canonical value to catch use-after-delete. This
> - * ends up being 0 on 32-bit KVM, but there's no better
> - * alternative.
> - */
> - hva = (unsigned long)(0xdeadull << 48);
> old_npages = slot->npages;
> + hva = 0;
> }
>
> for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
Under assumption that we can assume that access_ok(0,0) is safe to assume
to be always true:
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
I also tested exactly this solution when triaging this bug and it works,
but I wasn't sure that this is the correct solution.
Best regards,
Maxim Levitsky
^ permalink raw reply [flat|nested] 2+ messages in thread
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