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2ed90cb093
Read mmu_invalidate_seq before dropping the mmap_lock so that KVM can
detect if the results of vma_lookup() (e.g. vma_shift) become stale
before it acquires kvm->mmu_lock. This fixes a theoretical bug where a
VMA could be changed by userspace after vma_lookup() and before KVM
reads the mmu_invalidate_seq, causing KVM to install page table entries
based on a (possibly) no-longer-valid vma_shift.
Re-order the MMU cache top-up to earlier in user_mem_abort() so that it
is not done after KVM has read mmu_invalidate_seq (i.e. so as to avoid
inducing spurious fault retries).
It's unlikely that any sane userspace currently modifies VMAs in such a
way as to trigger this race. And even with directed testing I was unable
to reproduce it. But a sufficiently motivated host userspace might be
able to exploit this race.
Note KVM/ARM had the same bug and was fixed in a separate, near
identical patch (see Link).
Link: https://lore.kernel.org/kvm/20230313235454.2964067-1-dmatlack@google.com/
Fixes: 9955371cc0 ("RISC-V: KVM: Implement MMU notifiers")
Cc: stable@vger.kernel.org
Signed-off-by: David Matlack <dmatlack@google.com>
Tested-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Anup Patel <anup@brainfault.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.