On Fri, Oct 01, 2021, Colin King wrote:
> From: Colin Ian King <colin.king@xxxxxxxxxxxxx>
>
> The allocation for *gfn_track should be for a slot->npages lot of
> short integers, however the current allocation is using sizeof(*gfn_track)
> and that is the size of a pointer, which is too large. Fix this by
> using sizeof(**gfn_track) instead.
>
> Addresses-Coverity: ("Wrong sizeof argument")
> Fixes: 35b330bba6a7 ("KVM: x86: only allocate gfn_track when necessary")
> Signed-off-by: Colin Ian King <colin.king@xxxxxxxxxxxxx>
> ---
> arch/x86/kvm/mmu/page_track.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/mmu/page_track.c b/arch/x86/kvm/mmu/page_track.c
> index bb5d60bd4dbf..5b785a5f7dc9 100644
> --- a/arch/x86/kvm/mmu/page_track.c
> +++ b/arch/x86/kvm/mmu/page_track.c
> @@ -92,7 +92,7 @@ int kvm_page_track_enable_mmu_write_tracking(struct kvm *kvm)
> slots = __kvm_memslots(kvm, i);
> kvm_for_each_memslot(slot, slots) {
> gfn_track = slot->arch.gfn_track + KVM_PAGE_TRACK_WRITE;
> - *gfn_track = kvcalloc(slot->npages, sizeof(*gfn_track),
> + *gfn_track = kvcalloc(slot->npages, sizeof(**gfn_track),
> GFP_KERNEL_ACCOUNT);
Eww (not your patch, the original code). IMO the double indirection is completely
unnecessary, e.g. I find this far easier to follow
diff --git a/arch/x86/kvm/mmu/page_track.c b/arch/x86/kvm/mmu/page_track.c
index bb5d60bd4dbf..8cae41b831dd 100644
--- a/arch/x86/kvm/mmu/page_track.c
+++ b/arch/x86/kvm/mmu/page_track.c
@@ -75,7 +75,7 @@ int kvm_page_track_enable_mmu_write_tracking(struct kvm *kvm)
{
struct kvm_memslots *slots;
struct kvm_memory_slot *slot;
- unsigned short **gfn_track;
+ unsigned short *gfn_track;
int i;
if (write_tracking_enabled(kvm))
@@ -91,13 +91,13 @@ int kvm_page_track_enable_mmu_write_tracking(struct kvm *kvm)
for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
slots = __kvm_memslots(kvm, i);
kvm_for_each_memslot(slot, slots) {
- gfn_track = slot->arch.gfn_track + KVM_PAGE_TRACK_WRITE;
- *gfn_track = kvcalloc(slot->npages, sizeof(*gfn_track),
- GFP_KERNEL_ACCOUNT);
- if (*gfn_track == NULL) {
+ gfn_track = kvcalloc(slot->npages, sizeof(*gfn_track),
+ GFP_KERNEL_ACCOUNT);
+ if (gfn_track == NULL) {
mutex_unlock(&kvm->slots_arch_lock);
return -ENOMEM;
}
+ slot->arch.gfn_track[KVM_PAGE_TRACK_WRITE] = gfn_track;
}
}
> if (*gfn_track == NULL) {
> mutex_unlock(&kvm->slots_arch_lock);
Hrm, this fails to free the gfn_track allocations for previous memslots. The
on-demand rmaps code has the exact same bug (it frees rmaps for previous lpages
in the _current_ slot, but does not free previous slots).
And having two separate flows (and flags) for rmaps vs. gfn_track is pointless,
and means we have to maintain two near-identical copies of non-obvious code.
Paolo, is it too late to just drop the original deae4a10f166 ("KVM: x86: only
allocate gfn_track when necessary")?
> --
> 2.32.0
>
