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

[Brijesh Singh]

On 1/27/22 10:21 AM, Borislav Petkov wrote:
> 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".
Noted.

> >   
> > +/* Guest message request error code */
> > +#define SNP_GUEST_REQ_INVALID_LEN	BIT_ULL(32)
>
> SZ_4G is more descriptive, perhaps...

I am okay with using SZ_4G but per the spec they don't spell that its 4G 
size. It says bit 32 will should be set on error.



> > +
> > +	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?

Typically the sev_es_ghcb_hv_handler() is called from #VC handler, which 
provides the context structure. But in this and PSC case, the caller is 
not a #VC handler, so we don't have a context structure. But as you 
pointed, we could allocate context structure on the stack and pass it 
down so that verify_exception_info() does not cause a panic with NULL 
deference (when HV violates the spec and inject exception while handling 
this NAE).

thanks