linux-kernel - Re: [PATCH 1/2] virt: sev-guest: Allocate request data dynamically

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Message-ID: <d9d5a244-10c3-4e49-91d1-2b7de71bdd5c@amd.com>
Date: Fri, 7 Mar 2025 21:52:36 +1100
From: Alexey Kardashevskiy <aik@....com>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
 Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
 Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>,
 Tom Lendacky <thomas.lendacky@....com>, Nikunj A Dadhania <nikunj@....com>,
 Ard Biesheuvel <ardb@...nel.org>, Pavan Kumar Paluri <papaluri@....com>,
 Ashish Kalra <ashish.kalra@....com>, Paolo Bonzini <pbonzini@...hat.com>,
 Michael Roth <michael.roth@....com>,
 Kevin Loughlin <kevinloughlin@...gle.com>,
 Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>,
 Brijesh Singh <brijesh.singh@....com>, Liam Merwick
 <liam.merwick@...cle.com>, stable@...r.kernel.org, andreas.stuehrk@...i.tech
Subject: Re: [PATCH 1/2] virt: sev-guest: Allocate request data dynamically



On 7/3/25 12:36, Alexey Kardashevskiy wrote:
> From: Nikunj A Dadhania <nikunj@....com>
> 
> Commit ae596615d93d ("virt: sev-guest: Reduce the scope of SNP command
> mutex") narrowed the command mutex scope to snp_send_guest_request.
> However, GET_REPORT, GET_DERIVED_KEY, and GET_EXT_REPORT share the req
> structure in snp_guest_dev. Without the mutex protection, concurrent
> requests can overwrite each other's data. Fix it by dynamically allocating
> the request structure.
> 
> Fixes: ae596615d93d ("virt: sev-guest: Reduce the scope of SNP command mutex")
> Cc: stable@...r.kernel.org
> Reported-by: andreas.stuehrk@...i.tech
> Closes: https://github.com/AMDESE/AMDSEV/issues/265
> Signed-off-by: Nikunj A Dadhania <nikunj@....com>


oh. forgot:

Signed-off-by: Alexey Kardashevskiy <aik@....com>




> ---
>   drivers/virt/coco/sev-guest/sev-guest.c | 24 ++++++++++++--------
>   1 file changed, 15 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
> index ddec5677e247..4699fdc9ed44 100644
> --- a/drivers/virt/coco/sev-guest/sev-guest.c
> +++ b/drivers/virt/coco/sev-guest/sev-guest.c
> @@ -39,12 +39,6 @@ struct snp_guest_dev {
>   	struct miscdevice misc;
>   
>   	struct snp_msg_desc *msg_desc;
> -
> -	union {
> -		struct snp_report_req report;
> -		struct snp_derived_key_req derived_key;
> -		struct snp_ext_report_req ext_report;
> -	} req;
>   };
>   
>   /*
> @@ -72,7 +66,7 @@ struct snp_req_resp {
>   
>   static int get_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_ioctl *arg)
>   {
> -	struct snp_report_req *report_req = &snp_dev->req.report;
> +	struct snp_report_req *report_req __free(kfree) = NULL;
>   	struct snp_msg_desc *mdesc = snp_dev->msg_desc;
>   	struct snp_report_resp *report_resp;
>   	struct snp_guest_req req = {};
> @@ -81,6 +75,10 @@ static int get_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_io
>   	if (!arg->req_data || !arg->resp_data)
>   		return -EINVAL;
>   
> +	report_req = kzalloc(sizeof(*report_req), GFP_KERNEL_ACCOUNT);
> +	if (!report_req)
> +		return -ENOMEM;
> +
>   	if (copy_from_user(report_req, (void __user *)arg->req_data, sizeof(*report_req)))
>   		return -EFAULT;
>   
> @@ -117,7 +115,7 @@ static int get_report(struct snp_guest_dev *snp_dev, struct snp_guest_request_io
>   
>   static int get_derived_key(struct snp_guest_dev *snp_dev, struct snp_guest_request_ioctl *arg)
>   {
> -	struct snp_derived_key_req *derived_key_req = &snp_dev->req.derived_key;
> +	struct snp_derived_key_req *derived_key_req __free(kfree) = NULL;
>   	struct snp_derived_key_resp derived_key_resp = {0};
>   	struct snp_msg_desc *mdesc = snp_dev->msg_desc;
>   	struct snp_guest_req req = {};
> @@ -137,6 +135,10 @@ static int get_derived_key(struct snp_guest_dev *snp_dev, struct snp_guest_reque
>   	if (sizeof(buf) < resp_len)
>   		return -ENOMEM;
>   
> +	derived_key_req = kzalloc(sizeof(*derived_key_req), GFP_KERNEL_ACCOUNT);
> +	if (!derived_key_req)
> +		return -ENOMEM;
> +
>   	if (copy_from_user(derived_key_req, (void __user *)arg->req_data,
>   			   sizeof(*derived_key_req)))
>   		return -EFAULT;
> @@ -169,7 +171,7 @@ static int get_ext_report(struct snp_guest_dev *snp_dev, struct snp_guest_reques
>   			  struct snp_req_resp *io)
>   
>   {
> -	struct snp_ext_report_req *report_req = &snp_dev->req.ext_report;
> +	struct snp_ext_report_req *report_req __free(kfree) = NULL;
>   	struct snp_msg_desc *mdesc = snp_dev->msg_desc;
>   	struct snp_report_resp *report_resp;
>   	struct snp_guest_req req = {};
> @@ -179,6 +181,10 @@ static int get_ext_report(struct snp_guest_dev *snp_dev, struct snp_guest_reques
>   	if (sockptr_is_null(io->req_data) || sockptr_is_null(io->resp_data))
>   		return -EINVAL;
>   
> +	report_req = kzalloc(sizeof(*report_req), GFP_KERNEL_ACCOUNT);
> +	if (!report_req)
> +		return -ENOMEM;
> +
>   	if (copy_from_sockptr(report_req, io->req_data, sizeof(*report_req)))
>   		return -EFAULT;
>   

-- 
Alexey