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Description |
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In the Linux kernel, the following vulnerability has been resolved:
arm64: tlb: Fix TLBI RANGE operand
KVM/arm64 relies on TLBI RANGE feature to flush TLBs when the dirty
pages are collected by VMM and the page table entries become write
protected during live migration. Unfortunately, the operand passed
to the TLBI RANGE instruction isn't correctly sorted out due to the
commit 117940aa6e5f ("KVM: arm64: Define kvm_tlb_flush_vmid_range()").
It leads to crash on the destination VM after live migration because
TLBs aren't flushed completely and some of the dirty pages are missed.
For example, I have a VM where 8GB memory is assigned, starting from
0x40000000 (1GB). Note that the host has 4KB as the base page size.
In the middile of migration, kvm_tlb_flush_vmid_range() is executed
to flush TLBs. It passes MAX_TLBI_RANGE_PAGES as the argument to
__kvm_tlb_flush_vmid_range() and __flush_s2_tlb_range_op(). SCALE#3
and NUM#31, corresponding to MAX_TLBI_RANGE_PAGES, isn't supported
by __TLBI_RANGE_NUM(). In this specific case, -1 has been returned
from __TLBI_RANGE_NUM() for SCALE#3/2/1/0 and rejected by the loop
in the __flush_tlb_range_op() until the variable @scale underflows
and becomes -9, 0xffff708000040000 is set as the operand. The operand
is wrong since it's sorted out by __TLBI_VADDR_RANGE() according to
invalid @scale and @num.
Fix it by extending __TLBI_RANGE_NUM() to support the combination of
SCALE#3 and NUM#31. With the changes, [-1 31] instead of [-1 30] can
be returned from the macro, meaning the TLBs for 0x200000 pages in the
above example can be flushed in one shoot with SCALE#3 and NUM#31. The
macro TLBI_RANGE_MASK is dropped since no one uses it any more. The
comments are also adjusted accordingly.
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