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Subject: RE: [RFC PATCH V4 07/17] drivers: hv: Decrypt percpu hvcall input arg
 page in sev-snp enlightened guest
Thread-Topic: [RFC PATCH V4 07/17] drivers: hv: Decrypt percpu hvcall input
 arg page in sev-snp enlightened guest
Thread-Index: AQHZZlQQ0QYT0ni+r0KiuRqdlrSObK8nypUg
Date:   Wed, 12 Apr 2023 14:34:43 +0000
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References: <20230403174406.4180472-1-ltykernel@gmail.com>
 <20230403174406.4180472-8-ltykernel@gmail.com>
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From: Tianyu Lan <ltykernel@gmail.com> Sent: Monday, April 3, 2023 10:44 AM
>=20
> Hypervisor needs to access iput arg page and guest should decrypt
> the page.
>=20
> Signed-off-by: Tianyu Lan <tiala@microsoft.com>
> ---
> Change since RFC V3:
> 	* Use pgcount to decrypt memory.
>=20
> Change since RFC V2:
> 	* Set inputarg to be zero after kfree()
> 	* Not free mem when fail to encrypt mem in the hv_common_cpu_die().
> ---
>  drivers/hv/hv_common.c | 21 ++++++++++++++++++++-
>  1 file changed, 20 insertions(+), 1 deletion(-)
>=20
> diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
> index e3b04e978932..455432d49fd3 100644
> --- a/drivers/hv/hv_common.c
> +++ b/drivers/hv/hv_common.c
> @@ -21,6 +21,7 @@
>  #include <linux/ptrace.h>
>  #include <linux/slab.h>
>  #include <linux/dma-map-ops.h>
> +#include <linux/set_memory.h>
>  #include <asm/hyperv-tlfs.h>
>  #include <asm/mshyperv.h>
>=20
> @@ -128,6 +129,7 @@ int hv_common_cpu_init(unsigned int cpu)
>  	u64 msr_vp_index;
>  	gfp_t flags;
>  	int pgcount =3D hv_root_partition ? 2 : 1;
> +	int ret;
>=20
>  	/* hv_cpu_init() can be called with IRQs disabled from hv_resume() */
>  	flags =3D irqs_disabled() ? GFP_ATOMIC : GFP_KERNEL;
> @@ -137,6 +139,17 @@ int hv_common_cpu_init(unsigned int cpu)
>  	if (!(*inputarg))
>  		return -ENOMEM;
>=20
> +	if (hv_isolation_type_en_snp()) {
> +		ret =3D set_memory_decrypted((unsigned long)*inputarg, pgcount);
> +		if (ret) {
> +			kfree(*inputarg);
> +			*inputarg =3D NULL;
> +			return ret;
> +		}
> +
> +		memset(*inputarg, 0x00, PAGE_SIZE);

The memset() needs to use pgcount * PAGE_SIZE.

> +	}
> +
>  	if (hv_root_partition) {
>  		outputarg =3D (void **)this_cpu_ptr(hyperv_pcpu_output_arg);
>  		*outputarg =3D (char *)(*inputarg) + HV_HYP_PAGE_SIZE;
> @@ -156,6 +169,7 @@ int hv_common_cpu_die(unsigned int cpu)
>  {
>  	unsigned long flags;
>  	void **inputarg, **outputarg;
> +	int pgcount =3D hv_root_partition ? 2 : 1;
>  	void *mem;
>=20
>  	local_irq_save(flags);
> @@ -171,7 +185,12 @@ int hv_common_cpu_die(unsigned int cpu)
>=20
>  	local_irq_restore(flags);
>=20
> -	kfree(mem);
> +	if (hv_isolation_type_en_snp()) {
> +		if (!set_memory_encrypted((unsigned long)mem, pgcount))
> +			kfree(mem);
> +	} else {
> +		kfree(mem);
> +	}
>=20
>  	return 0;
>  }
> --
> 2.25.1