linux-kernel - RE: [RFC PATCH V2 10/18] drivers: hv: Decrypt percpu hvcall input arg page in sev-snp enlightened guest

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Message-ID: <BYAPR21MB168878729E4A76AFC9B3E053D7E09@BYAPR21MB1688.namprd21.prod.outlook.com>
Date:   Wed, 14 Dec 2022 18:16:00 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     Tianyu Lan <ltykernel@...il.com>,
        "luto@...nel.org" <luto@...nel.org>,
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        "jgross@...e.com" <jgross@...e.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
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CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
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Subject: RE: [RFC PATCH V2 10/18] drivers: hv: Decrypt percpu hvcall input arg
 page in sev-snp enlightened guest

From: Tianyu Lan <ltykernel@...il.com> Sent: Friday, November 18, 2022 7:46 PM
> 
> Hypervisor needs to access iput arg page and guest should decrypt
> the page.
> 
> Signed-off-by: Tianyu Lan <tiala@...rosoft.com>
> ---
>  drivers/hv/hv_common.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
> index 2c6602571c47..c16961e686a0 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>
> 
> @@ -125,6 +126,7 @@ int hv_common_cpu_init(unsigned int cpu)
>  	u64 msr_vp_index;
>  	gfp_t flags;
>  	int pgcount = hv_root_partition ? 2 : 1;
> +	int ret;
> 
>  	/* hv_cpu_init() can be called with IRQs disabled from hv_resume() */
>  	flags = irqs_disabled() ? GFP_ATOMIC : GFP_KERNEL;
> @@ -134,6 +136,16 @@ int hv_common_cpu_init(unsigned int cpu)
>  	if (!(*inputarg))
>  		return -ENOMEM;
> 
> +	if (hv_isolation_type_en_snp()) {
> +		ret = set_memory_decrypted((unsigned long)*inputarg, 1);
> +		if (ret) {
> +			kfree(*inputarg);

After the kfree(), set *inputarg back to NULL.  There's other code that
tests the value of *inputarg to know if the per-CPU hypercall page has
been successfully allocated.

> +			return ret;
> +		}
> +
> +		memset(*inputarg, 0x00, PAGE_SIZE);
> +	}
> +
>  	if (hv_root_partition) {
>  		outputarg = (void **)this_cpu_ptr(hyperv_pcpu_output_arg);
>  		*outputarg = (char *)(*inputarg) + HV_HYP_PAGE_SIZE;
> @@ -168,6 +180,9 @@ int hv_common_cpu_die(unsigned int cpu)
> 
>  	local_irq_restore(flags);
> 
> +	if (hv_isolation_type_en_snp())
> +		set_memory_encrypted((unsigned long)mem, 1);
> +
>  	kfree(mem);
> 
>  	return 0;
> --
> 2.25.1