Re: [PATCH 0/4] KVM: arm64: Fix host access to the EL2 stacks

[Vincent Donnefort <vdonnefort@google.com>]

On Tue, Sep 08, 2026 at 12:07:09PM +0100, Fuad Tabba wrote:
> Hi folks,
> 
> The per-CPU EL2 stacks are initialised as host-owned after pKVM init.
> fix_host_ownership() walks only the linear-map alias of each memblock
> region, and the stacks, mapped in the private VA range for their guard
> pages, have none.
> 
> Patch 1 is the fix, and it needs none of the other three. Patch 4 adds
> the check that would have caught it and would catch similar instances
> in the future: once the transfer is done, walk the private VA range and
> fail init unless every valid leaf is hyp-owned, or is hyp text mapped
> without write access.
> 
> Patch 2 is a fix in its own right, but to a different bug.
> fix_host_ownership_walker() matches hyp text on its stage-1 permissions,
> and that test hasn't matched on a non-hVHE host since 7.0, so hyp text
> is donated there rather than left read-only. Nothing crashes, but the
> instruction dump on hyp panic reads a page the host can't access, so
> the Code: line comes out as question marks. It matches by physical
> address instead, which is what patch 4 needs too. Patch 3 splits the
> start of the range from the allocation cursor, with no functional
> change, so patch 4 knows where the range begins.
> 
> Based on Linux 7.3-rc2 (df2908090cda3).
> 
> Cheers,
> /fuad
> 
> Fuad Tabba (4):
>   KVM: arm64: Transfer the hyp stack pages out of the host stage-2
>   KVM: arm64: Match hyp text by physical address in fix_host_ownership()
>   KVM: arm64: Move the private VA allocation cursor to __io_map_next
>   KVM: arm64: Check every private mapping is hyp-owned at pKVM init
> 
>  arch/arm64/kvm/hyp/include/nvhe/mem_protect.h |  2 +
>  arch/arm64/kvm/hyp/include/nvhe/mm.h          |  1 +
>  arch/arm64/kvm/hyp/nvhe/mem_protect.c         | 20 +++++
>  arch/arm64/kvm/hyp/nvhe/mm.c                  | 79 ++++++++++++++++---
>  arch/arm64/kvm/hyp/nvhe/setup.c               | 16 +++-
>  5 files changed, 108 insertions(+), 10 deletions(-)
> 
> 
> base-commit: df2908090cda368b01ff43709f51890076c56157
> -- 
> 2.39.5
> 

Reviewed-by: Vincent Donnefort <vdonnefort@google.com>
Tested-by: Vincent Donnefort <vdonnefort@google.com>

-- 
Vincent