Messages in this thread |  | | Date | Wed, 29 Dec 2021 12:09:01 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH v8 15/40] x86/mm: Add support to validate memory when changing C-bit |
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On Fri, Dec 10, 2021 at 09:43:07AM -0600, Brijesh Singh wrote: > The set_memory_{encrypt,decrypt}() are used for changing the pages
$ git grep -E "set_memory_decrypt\W" $
Please check all your commit messages whether you're quoting the proper functions.
> from decrypted (shared) to encrypted (private) and vice versa. > When SEV-SNP is active, the page state transition needs to go through > additional steps.
... "done by the guest."
I think it is important to state here who's supposed to do those additional steps.
...
> @@ -659,6 +659,161 @@ void __init snp_prep_memory(unsigned long paddr, unsigned int sz, enum psc_op op > WARN(1, "invalid memory op %d\n", op); > } > > +static int vmgexit_psc(struct snp_psc_desc *desc) > +{ > + int cur_entry, end_entry, ret = 0; > + struct snp_psc_desc *data; > + struct ghcb_state state; > + unsigned long flags; > + struct ghcb *ghcb; > + > + /* __sev_get_ghcb() need to run with IRQs disabled because it using per-cpu GHCB */
"... because it uses a per-CPU GHCB."
> + local_irq_save(flags); > + > + ghcb = __sev_get_ghcb(&state); > + if (unlikely(!ghcb)) > + panic("SEV-SNP: Failed to get GHCB\n");
__sev_get_ghcb() will already panic if even the backup GHCB is active so you don't need to panic here too - just check the retval.
> + /* Copy the input desc into GHCB shared buffer */ > + data = (struct snp_psc_desc *)ghcb->shared_buffer; > + memcpy(ghcb->shared_buffer, desc, min_t(int, GHCB_SHARED_BUF_SIZE, sizeof(*desc))); > + > + /* > + * As per the GHCB specification, the hypervisor can resume the guest > + * before processing all the entries. Check whether all the entries > + * are processed. If not, then keep retrying. > + * > + * The stragtegy here is to wait for the hypervisor to change the page
+ * The stragtegy here is to wait for the hypervisor to change the page Unknown word [stragtegy] in comment, suggestions: ['strategy', 'strategist']
> + * state in the RMP table before guest accesses the memory pages. If the > + * page state change was not successful, then later memory access will result > + * in a crash. > + */ > + cur_entry = data->hdr.cur_entry; > + end_entry = data->hdr.end_entry; > + > + while (data->hdr.cur_entry <= data->hdr.end_entry) { > + ghcb_set_sw_scratch(ghcb, (u64)__pa(data)); > +
Add a comment here:
/* This will advance the shared buffer data points to. */
I had asked about it already but nada:
"So then you *absoulutely* want to use data->hdr everywhere and then also write why in the comment above the check that data gets updated by the HV call."
> + ret = sev_es_ghcb_hv_call(ghcb, true, NULL, SVM_VMGEXIT_PSC, 0, 0); > + > + /* > + * Page State Change VMGEXIT can pass error code through > + * exit_info_2. > + */ > + if (WARN(ret || ghcb->save.sw_exit_info_2, > + "SEV-SNP: PSC failed ret=%d exit_info_2=%llx\n", > + ret, ghcb->save.sw_exit_info_2)) { > + ret = 1; > + goto out; > + } > + > + /* Verify that reserved bit is not set */ > + if (WARN(data->hdr.reserved, "Reserved bit is set in the PSC header\n")) { > + ret = 1; > + goto out; > + } > + > + /* > + * Sanity check that entry processing is not going backward.
"... backwards."
> + * This will happen only if hypervisor is tricking us. > + */ > + if (WARN(data->hdr.end_entry > end_entry || cur_entry > data->hdr.cur_entry, > +"SEV-SNP: PSC processing going backward, end_entry %d (got %d) cur_entry %d (got %d)\n", > + end_entry, data->hdr.end_entry, cur_entry, data->hdr.cur_entry)) { > + ret = 1; > + goto out; > + } > + } > + > +out: > + __sev_put_ghcb(&state); > + local_irq_restore(flags); > + > + return ret; > +} > + > +static void __set_pages_state(struct snp_psc_desc *data, unsigned long vaddr, > + unsigned long vaddr_end, int op) > +{ > + struct psc_hdr *hdr; > + struct psc_entry *e; > + unsigned long pfn; > + int i; > + > + hdr = &data->hdr; > + e = data->entries; > + > + memset(data, 0, sizeof(*data)); > + i = 0; > + > + while (vaddr < vaddr_end) { > + if (is_vmalloc_addr((void *)vaddr)) > + pfn = vmalloc_to_pfn((void *)vaddr); > + else > + pfn = __pa(vaddr) >> PAGE_SHIFT; > + > + e->gfn = pfn; > + e->operation = op; > + hdr->end_entry = i;
/* * Current SNP implementation doesn't keep track of the page size so use * 4K for simplicity. */
> + e->pagesize = RMP_PG_SIZE_4K; > + > + vaddr = vaddr + PAGE_SIZE; > + e++; > + i++; > + }
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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