Re: [PATCH v8 36/40] x86/sev: Provide support for SNP guest request NAEs

Borislav Petkov
2022-01-27T16:21:17Z

On Fri, Dec 10, 2021 at 09:43:28AM -0600, Brijesh Singh wrote:
> Version 2 of GHCB specification provides SNP_GUEST_REQUEST and
> SNP_EXT_GUEST_REQUEST NAE that can be used by the SNP guest to communicate
> with the PSP.
>
> While at it, add a snp_issue_guest_request() helper that can be used by

Not "that can" but "that will".

> driver or other subsystem to issue the request to PSP.
>
> See SEV-SNP and GHCB spec for more details.
>
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> ---
> arch/x86/include/asm/sev-common.h | 3 ++
> arch/x86/include/asm/sev.h | 14 +++++++++
> arch/x86/include/uapi/asm/svm.h | 4 +++
> arch/x86/kernel/sev.c | 51 +++++++++++++++++++++++++++++++
> 4 files changed, 72 insertions(+)
>
> diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
> index 673e6778194b..346600724b84 100644
> --- a/arch/x86/include/asm/sev-common.h
> +++ b/arch/x86/include/asm/sev-common.h
> @@ -128,6 +128,9 @@ struct snp_psc_desc {
> struct psc_entry entries[VMGEXIT_PSC_MAX_ENTRY];
> } __packed;
>
> +/* Guest message request error code */
> +#define SNP_GUEST_REQ_INVALID_LEN BIT_ULL(32)

SZ_4G is more descriptive, perhaps...

> +int snp_issue_guest_request(u64 exit_code, struct snp_req_data *input, unsigned long *fw_err)
> +{
> + struct ghcb_state state;
> + unsigned long flags;
> + struct ghcb *ghcb;
> + int ret;
> +
> + if (!cc_platform_has(CC_ATTR_SEV_SNP))
> + return -ENODEV;
> +
> + /* __sev_get_ghcb() need to run with IRQs disabled because it using per-cpu GHCB */

needs it is using a

> + local_irq_save(flags);
> +
> + ghcb = __sev_get_ghcb(&state);
> + if (!ghcb) {
> + ret = -EIO;
> + goto e_restore_irq;
> + }
> +
> + vc_ghcb_invalidate(ghcb);
> +
> + if (exit_code == SVM_VMGEXIT_EXT_GUEST_REQUEST) {
> + ghcb_set_rax(ghcb, input->data_gpa);
> + ghcb_set_rbx(ghcb, input->data_npages);
> + }
> +
> + ret = sev_es_ghcb_hv_call(ghcb, true, NULL, exit_code, input->req_gpa, input->resp_gpa);
^^^^^

That's ctxt which is accessed without a NULL check in
verify_exception_info().

Why aren't you allocating a ctxt on stack like the other callers do?

--
Regards/Gruss,
Boris.