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From: Janosch Frank <frankja@linux.ibm.com>
To: Claudio Imbrenda <imbrenda@linux.ibm.com>, kvm@vger.kernel.org
Cc: cohuck@redhat.com, borntraeger@de.ibm.com, thuth@redhat.com,
	pasic@linux.ibm.com, david@redhat.com,
	linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 05/13] KVM: s390: pv: handle secure storage exceptions for normal guests
Date: Thu, 29 Jul 2021 14:17:11 +0200	[thread overview]
Message-ID: <103c158c-dba6-7421-af8d-4d771c1cf087@linux.ibm.com> (raw)
In-Reply-To: <20210728142631.41860-6-imbrenda@linux.ibm.com>

On 7/28/21 4:26 PM, Claudio Imbrenda wrote:
> With upcoming patches, normal guests might touch secure pages.
> 
> This patch extends the existing exception handler to convert the pages
> to non secure also when the exception is triggered by a normal guest.
> 
> This can happen for example when a secure guest reboots; the first
> stage of a secure guest is non secure, and in general a secure guest
> can reboot into non-secure mode.
> 
> If the secure memory of the previous boot has not been cleared up
> completely yet, a non-secure guest might touch secure memory, which
> will need to be handled properly.
> 
> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> ---
>  arch/s390/mm/fault.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
> index eb68b4f36927..b89d625ea2ec 100644
> --- a/arch/s390/mm/fault.c
> +++ b/arch/s390/mm/fault.c
> @@ -767,6 +767,7 @@ void do_secure_storage_access(struct pt_regs *regs)
>  	struct vm_area_struct *vma;
>  	struct mm_struct *mm;
>  	struct page *page;
> +	struct gmap *gmap;
>  	int rc;
>  
>  	/*
> @@ -796,6 +797,16 @@ void do_secure_storage_access(struct pt_regs *regs)
>  	}
>  
>  	switch (get_fault_type(regs)) {
> +	case GMAP_FAULT:
> +		gmap = (struct gmap *)S390_lowcore.gmap;
> +		/*
> +		 * Very unlikely, but if it happens, simply try again.
> +		 * The next attempt will trigger a different exception.
> +		 */

If we keep this the way it currently is then the comment needs to go to
the EFAULT check since it makes no sense above the gmap_translate().

> +		addr = __gmap_translate(gmap, addr);

So we had a valid gmap PTE to end up here where the guest touched a
secure page and triggered the exception. But we suddenly can't translate
the gaddr to a vmaddr because the gmap tracking doesn't have an entry
for the address.

My first instinct is to SIGSEGV the process since I can't come up with a
way out of this situation except for the process to map this back in.
The only reason I can think of that it was removed from the mapping is
malicious intent or a bug.

I think this is needs a VM_FAULT_BADMAP and a do_fault_error() call.

> +		if (addr == -EFAULT)
> +			break;
> +		fallthrough;
>  	case USER_FAULT:
>  		mm = current->mm;
>  		mmap_read_lock(mm);
> @@ -824,7 +835,6 @@ void do_secure_storage_access(struct pt_regs *regs)
>  		if (rc)
>  			BUG();
>  		break;
> -	case GMAP_FAULT:
>  	default:
>  		do_fault_error(regs, VM_READ | VM_WRITE, VM_FAULT_BADMAP);
>  		WARN_ON_ONCE(1);
> 


  reply	other threads:[~2021-07-29 12:17 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-28 14:26 [PATCH v2 00/13] KVM: s390: pv: implement lazy destroy Claudio Imbrenda
2021-07-28 14:26 ` [PATCH v2 01/13] KVM: s390: pv: avoid stall notifications for some UVCs Claudio Imbrenda
2021-07-29  9:58   ` Janosch Frank
2021-07-29 12:52     ` Claudio Imbrenda
2021-07-29 10:49   ` Cornelia Huck
2021-07-29 13:22     ` Claudio Imbrenda
2021-07-28 14:26 ` [PATCH v2 02/13] KVM: s390: pv: leak the ASCE page when destroy fails Claudio Imbrenda
2021-07-29 10:41   ` Janosch Frank
2021-07-29 12:54     ` Claudio Imbrenda
2021-07-29 13:45       ` Janosch Frank
2021-07-28 14:26 ` [PATCH v2 03/13] KVM: s390: pv: properly handle page flags for protected guests Claudio Imbrenda
2021-07-29 11:43   ` Janosch Frank
2021-07-28 14:26 ` [PATCH v2 04/13] KVM: s390: pv: handle secure storage violations " Claudio Imbrenda
2021-07-28 14:26 ` [PATCH v2 05/13] KVM: s390: pv: handle secure storage exceptions for normal guests Claudio Imbrenda
2021-07-29 12:17   ` Janosch Frank [this message]
2021-07-29 13:28     ` Claudio Imbrenda
2021-07-28 14:26 ` [PATCH v2 06/13] KVM: s390: pv: refactor s390_reset_acc Claudio Imbrenda
2021-07-28 14:26 ` [PATCH v2 07/13] KVM: s390: pv: usage counter instead of flag Claudio Imbrenda
2021-07-28 14:26 ` [PATCH v2 08/13] KVM: s390: pv: add export before import Claudio Imbrenda
2021-07-28 14:26 ` [PATCH v2 09/13] KVM: s390: pv: lazy destroy for reboot Claudio Imbrenda
2021-07-28 14:26 ` [PATCH v2 10/13] KVM: s390: pv: extend lazy destroy to handle shutdown Claudio Imbrenda
2021-07-28 14:26 ` [PATCH v2 11/13] KVM: s390: pv: module parameter to fence lazy destroy Claudio Imbrenda
2021-07-28 14:26 ` [PATCH v2 12/13] KVM: s390: pv: add OOM notifier for " Claudio Imbrenda
2021-07-28 14:26 ` [PATCH v2 13/13] KVM: s390: pv: add support for UV feature bits Claudio Imbrenda
2021-07-29  9:52   ` Janosch Frank
2021-07-29 13:28     ` Claudio Imbrenda

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