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UPSTREAM: KVM: arm64: Set the MTE tag bit before releasing the page

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Setting a page flag without holding a reference to the page
is living dangerously. In the tag-writing path, we drop the
reference to the page by calling kvm_release_pfn_dirty(),
and only then set the PG_mte_tagged bit.

It would be safer to do it the other way round.

Fixes: f0376edb1d ("KVM: arm64: Add ioctl to fetch/store tags in a guest")
Cc: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/87k0mjidwb.wl-maz@kernel.org
(cherry picked from commit 98db7259fa)
Signed-off-by: Will Deacon <willdeacon@google.com>
Bug: 192636784
Change-Id: Iea5ad082147127c19a580c98629ac60c696092f8
This commit is contained in:
Marc Zyngier
2021-06-24 14:21:05 +01:00
committed by Will Deacon
parent 71c05826d6
commit 663bbfa2a4
1 changed files with 8 additions and 4 deletions
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12
arch/arm64/kvm/guest.c
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@@ -1058,6 +1058,14 @@ long kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm,
} else {
num_tags = mte_copy_tags_from_user(maddr, tags,
MTE_GRANULES_PER_PAGE);
/*
* Set the flag after checking the write
* completed fully
*/
if (num_tags == MTE_GRANULES_PER_PAGE)
set_bit(PG_mte_tagged, &page->flags);
kvm_release_pfn_dirty(pfn);
}
@@ -1066,10 +1074,6 @@ long kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm,
goto out;
}
/* Set the flag after checking the write completed fully */
if (write)
set_bit(PG_mte_tagged, &page->flags);
gfn++;
tags += num_tags;
length -= PAGE_SIZE;