linux-kernel - Re: [PATCH v4 3/4] virt/coco/sev-guest: Remove err in handle_guest

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Date:   Fri, 28 Oct 2022 09:46:43 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Dionna Glaze <dionnaglaze@...gle.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Joerg Roedel <jroedel@...e.de>,
        Peter Gonda <pgonda@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v4 3/4] virt/coco/sev-guest: Remove err in
 handle_guest_request

On 10/24/22 17:46, Dionna Glaze wrote:
> The err variable may not be set in the call to snp_issue_guest_request,
> yet it is unconditionally written back to fw_err if fw_err is non-null.
> This is undefined behavior, and currently returns uninitialized kernel
> stack memory to user space.
> 
> The fw_err argument is better to just pass through to
> snp_issue_guest_request, so we do that. Since the issue_request's
> signature has changed fw_err to exitinfo2, we change the argument name
> here.
> 
> Cc: Tom Lendacky <Thomas.Lendacky@....com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Joerg Roedel <jroedel@...e.de>
> Cc: Peter Gonda <pgonda@...gle.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> Fixes: fce96cf04430 ("virt: Add SEV-SNP guest driver")
> Signed-off-by: Dionna Glaze <dionnaglaze@...gle.com>

Reviewed-by: Tom Lendacky <thomas.lendacky@....com>

> ---
>   drivers/virt/coco/sev-guest/sev-guest.c | 7 ++-----
>   1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
> index f422f9c58ba7..0508c2f46f6b 100644
> --- a/drivers/virt/coco/sev-guest/sev-guest.c
> +++ b/drivers/virt/coco/sev-guest/sev-guest.c
> @@ -303,9 +303,8 @@ static int enc_payload(struct snp_guest_dev *snp_dev, u64 seqno, int version, u8
>   
>   static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, int msg_ver,
>   				u8 type, void *req_buf, size_t req_sz, void *resp_buf,
> -				u32 resp_sz, __u64 *fw_err)
> +				u32 resp_sz, __u64 *exitinfo2)
>   {
> -	unsigned long err;
>   	u64 seqno;
>   	int rc;
>   
> @@ -322,9 +321,7 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
>   		return rc;
>   
>   	/* Call firmware to process the request */
> -	rc = snp_issue_guest_request(exit_code, &snp_dev->input, &err);
> -	if (fw_err)
> -		*fw_err = err;
> +	rc = snp_issue_guest_request(exit_code, &snp_dev->input, exitinfo2);
>   
>   	if (rc)
>   		return rc;