linux-kernel - Re: [PATCH v7 3/4] virt: sev-guest: Remove err in handle_guest

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Message-ID: <CAMkAt6oPMgAEewMDaf+gdJ+D5bXe6dZX0ty0nGp_NWgaymxXcg@mail.gmail.com>
Date:   Fri, 4 Nov 2022 15:47:31 -0600
From:   Peter Gonda <pgonda@...gle.com>
To:     Dionna Glaze <dionnaglaze@...gle.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Tom Lendacky <Thomas.Lendacky@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Joerg Roedel <jroedel@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Borislav Petkov <bp@...e.de>, Haowen Bai <baihaowen@...zu.com>,
        Liam Merwick <liam.merwick@...cle.com>,
        Yang Yingliang <yangyingliang@...wei.com>
Subject: Re: [PATCH v7 3/4] virt: sev-guest: Remove err in handle_guest_request

On Fri, Nov 4, 2022 at 2:16 PM Dionna Glaze <dionnaglaze@...gle.com> 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>
> Cc: Borislav Petkov <bp@...e.de>
> Cc: Haowen Bai <baihaowen@...zu.com>
> Cc: Liam Merwick <liam.merwick@...cle.com>
> Cc: Yang Yingliang <yangyingliang@...wei.com>
>
> Fixes: fce96cf04430 ("virt: Add SEV-SNP guest driver")
> Signed-off-by: Dionna Glaze <dionnaglaze@...gle.com>
> ---
>  drivers/virt/coco/sev-guest/sev-guest.c | 14 +++++---------
>  1 file changed, 5 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/virt/coco/sev-guest/sev-guest.c b/drivers/virt/coco/sev-guest/sev-guest.c
> index d08ff87c2dac..5ebf87651299 100644
> --- a/drivers/virt/coco/sev-guest/sev-guest.c
> +++ b/drivers/virt/coco/sev-guest/sev-guest.c
> @@ -322,9 +322,8 @@ 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)

I was off before, but handle_guest_request() is actually the function
Borislav suggested tweaking. Why don't we update
handle_guest_request() to take snp_guest_request_ioctl here since we
are already updating all the call sites in the next patch.