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commit13ec9308a8upstream. 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). This bug has existed since KVM/ARM's inception. 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. Fixes:94f8e6418d("KVM: ARM: Handle guest faults in KVM") Cc: stable@vger.kernel.org Reported-by: Sean Christopherson <seanjc@google.com> Signed-off-by: David Matlack <dmatlack@google.com> Reviewed-by: Marc Zyngier <maz@kernel.org> Link: https://lore.kernel.org/r/20230313235454.2964067-1-dmatlack@google.com Signed-off-by: Oliver Upton <oliver.upton@linux.dev> [will: Use FSC_PERM instead of ESR_ELx_FSC_PERM. Read 'mmu_notifier_seq' instead of 'mmu_invalidate_seq'. Fix up function references in comment.] Signed-off-by: Will Deacon <will@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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.