2022-10-25 00:28:56

by Dionna Amalie Glaze

Subject: [PATCH v4 3/4] virt/coco/sev-guest: Remove err in handle_guest_request

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 <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Joerg Roedel <[email protected]>
Cc: Peter Gonda <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Dave Hansen <[email protected]>

Fixes: fce96cf04430 ("virt: Add SEV-SNP guest driver")
Signed-off-by: Dionna Glaze <[email protected]>
---
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;
--
2.38.0.135.g90850a2211-goog

2022-10-28 15:09:12

by Tom Lendacky

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 <[email protected]>
> Cc: Paolo Bonzini <[email protected]>
> Cc: Joerg Roedel <[email protected]>
> Cc: Peter Gonda <[email protected]>
> Cc: Thomas Gleixner <[email protected]>
> Cc: Dave Hansen <[email protected]>
>
> Fixes: fce96cf04430 ("virt: Add SEV-SNP guest driver")
> Signed-off-by: Dionna Glaze <[email protected]>

Reviewed-by: Tom Lendacky <[email protected]>

> ---
> 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;