Messages in this thread | | | Date | Mon, 2 May 2022 09:02:27 -0700 | Subject | Re: [PATCH v5 3/3] x86/tdx: Add Quote generation support | From | Sathyanarayanan Kuppuswamy <> |
| |
Hi Kai,
On 5/1/22 10:01 PM, Kai Huang wrote: > >> + >> +static long tdx_get_quote(void __user *argp) >> +{ >> + struct tdx_quote_req quote_req; >> + long ret = 0; >> + int order; >> + >> + /* Hold lock to serialize GetQuote requests */ >> + mutex_lock("e_lock); >> + >> + reinit_completion(&req_compl); >> + >> + /* Copy GetQuote request struct from user buffer */ >> + if (copy_from_user("e_req, argp, sizeof(struct tdx_quote_req))) { >> + ret = -EFAULT; >> + goto quote_failed; >> + } >> + >> + /* Make sure the length & timeout is valid */ >> + if (!quote_req.len || !quote_req.timeout) { >> + ret = -EINVAL; >> + goto quote_failed; >> + } >> + >> + /* Get order for Quote buffer page allocation */ >> + order = get_order(quote_req.len); >> + >> + /* >> + * Allocate buffer to get TD Quote from the VMM. >> + * Size needs to be 4KB aligned (which is already >> + * met in page allocation). >> + */ >> + tdquote = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, order); >> + if (!tdquote) { >> + ret = -ENOMEM; >> + goto quote_failed; >> + } >> + >> + /* >> + * Since this buffer will be shared with the VMM via GetQuote >> + * hypercall, decrypt it. >> + */ >> + ret = set_memory_decrypted((unsigned long)tdquote, 1UL << order); >> + if (ret) >> + goto quote_failed; >> + >> + /* Copy TDREPORT from user buffer to kernel Quote buffer */ >> + if (copy_from_user(tdquote, (void __user *)quote_req.buf, quote_req.len)) { >> + ret = -EFAULT; >> + goto quote_failed; >> + } >> + >> + /* Submit GetQuote Request */ >> + ret = tdx_get_quote_hypercall(tdquote, (1ULL << order) * PAGE_SIZE); >> + if (ret) { >> + pr_err("GetQuote hypercall failed, status:%lx\n", ret); >> + ret = -EIO; >> + goto quote_failed; >> + } >> + >> + /* Wait for attestation completion */ >> + ret = wait_for_completion_interruptible(&req_compl); >> + if (ret <= 0) { >> + ret = -EIO; >> + goto quote_failed; >> + } >> + >> + /* Copy output data back to user buffer */ >> + if (copy_to_user((void __user *)quote_req.buf, tdquote, quote_req.len)) >> + ret = -EFAULT; >> + >> +quote_failed: >> + if (tdquote) >> + free_pages((unsigned long)tdquote, order); > > The buffer is freed w/o being converted back to private. How can you prevent > the buffer from being allocated by kernel and used as private pages again?
Yes. It needs set_memory_encrypted() call here. I will fix this in next version.
> > Also, the buffer may be still used by VMM when timeout (IN_FLIGHT), how can > this even work?
We will never reach here for IN_FLIGHT case. We will block in wait_for_completion_interruptible() till the status changes to success or failure.
> >> + tdquote = NULL; >> + mutex_unlock("e_lock); >> + return ret; >> +} >> + >> +static void attestation_callback_handler(void) >> +{ >> + struct tdx_quote_hdr *quote_hdr; >> + >> + quote_hdr = (struct tdx_quote_hdr *) tdquote; >> + >> + /* Check for spurious callback IRQ case */ >> + if (!tdquote || quote_hdr->status == GET_QUOTE_IN_FLIGHT) >> + return; > > I don't get the logic. Please explain.
I am trying to handle spurious IRQ case here. If we receive a callback IRQ from VMM before even we allocate tdquote or post the GetQuote request, accessing quote_hdr->status will lead to NULL pointer exception. So I have added check for valid quote buffer (tdquote != NULL)
Second condition (quote_hdr->status == GET_QUOTE_IN_FLIGHT)) makes sure we don't mark the current quote request complete until the Quote buffer status changes to GET_QUOTE_SUCCESS, GET_QUOTE_ERROR or GET_QUOTE_SERVICE_UNAVAILABLE.
> >> + >> + complete(&req_compl); >> +} >> + >
-- Sathyanarayanan Kuppuswamy Linux Kernel Developer
| |