Re: [PATCH] KVM: arm64: Unregister HYP sections from kmemleak in protected mode

[Quentin Perret <qperret@google.com>]

On Thursday 29 Jul 2021 at 14:50:16 (+0100), Marc Zyngier wrote:
> Booting a KVM host in protected mode with kmemleak quickly results
> in a pretty bad crash, as kmemleak doesn't know that the HYP sections
> have been taken away.
> 
> Make the unregistration from kmemleak part of marking the sections
> as HYP-private. The rest of the HYP-specific data is obtained via
> the page allocator, which is not subjected to kmemleak.
> 
> Fixes: 90134ac9cabb ("KVM: arm64: Protect the .hyp sections from the host")
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> Cc: Quentin Perret <qperret@google.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: stable@vger.kernel.org # 5.13
> ---
>  arch/arm64/kvm/arm.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index e9a2b8f27792..23f12e602878 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -15,6 +15,7 @@
>  #include <linux/fs.h>
>  #include <linux/mman.h>
>  #include <linux/sched.h>
> +#include <linux/kmemleak.h>
>  #include <linux/kvm.h>
>  #include <linux/kvm_irqfd.h>
>  #include <linux/irqbypass.h>
> @@ -1960,8 +1961,12 @@ static inline int pkvm_mark_hyp(phys_addr_t start, phys_addr_t end)
>  }
>  
>  #define pkvm_mark_hyp_section(__section)		\
> +({							\
> +	u64 sz = __section##_end - __section##_start;	\
> +	kmemleak_free_part(__section##_start, sz);	\
>  	pkvm_mark_hyp(__pa_symbol(__section##_start),	\
> -			__pa_symbol(__section##_end))
> +		      __pa_symbol(__section##_end));	\
> +})

At some point we should also look into unmapping these sections from
EL1 stage-1 as well, as that should lead to better error messages in
case the host accesses hyp-private memory some other way. But this
patch makes sense on its own, so:

Reviewed-by: Quentin Perret <qperret@google.com>

Thanks,
Quentin