linux-kernel - Re: [PATCH v2] virt/coco/sev-guest: Remove err in handle_guest

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Message-ID: <3265d311-0e02-6e98-377a-d93a5d0b90cc@amd.com>
Date:   Wed, 19 Oct 2022 15:32:10 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Dionna Glaze <dionnaglaze@...gle.com>, x86@...nel.org,
        linux-kernel@...r.kernel.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 v2] virt/coco/sev-guest: Remove err in
 handle_guest_request

On 10/19/22 14:58, 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.
> 
> 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>
> 
> Signed-off-by: Dionna Glaze <dionnaglaze@...gle.com>

You should include a Fixes: tag.

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

Also, you may want to base your other series [1] on this one, since you'll
likely get conflicts if this is applied first.

[1] https://lore.kernel.org/lkml/20221019173537.1238121-1-dionnaglaze@google.com/

Thanks,
Tom

> ---
>   drivers/virt/coco/sev-guest/sev-guest.c | 5 +----
>   1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
> index f422f9c58ba7..00708b4491e0 100644
> --- a/drivers/virt/coco/sev-guest/sev-guest.c
> +++ b/drivers/virt/coco/sev-guest/sev-guest.c
> @@ -305,7 +305,6 @@ static int handle_guest_request(struct snp_guest_dev *snp_dev, u64 exit_code, in
>   				u8 type, void *req_buf, size_t req_sz, void *resp_buf,
>   				u32 resp_sz, __u64 *fw_err)
>   {
> -	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, fw_err);
>   
>   	if (rc)
>   		return rc;