Re: [PATCH v41 20/24] selftests/x86: Add a selftest for SGX

Jarkko Sakkinen
2020-11-17T21:28:13Z

On Tue, Nov 17, 2020 at 06:26:50PM +0100, Borislav Petkov wrote:
> On Fri, Nov 13, 2020 at 12:01:31AM +0200, Jarkko Sakkinen wrote:
> > +bool encl_load(const char *path, struct encl *encl)
> > +{
> > + Elf64_Phdr *phdr_tbl;
> > + off_t src_offset;
> > + Elf64_Ehdr *ehdr;
> > + int i, j;
> > + int ret;
> > +
> > + memset(encl, 0, sizeof(*encl));
> > +
> > + ret = open("/dev/sgx_enclave", O_RDWR);
> > + if (ret < 0) {
> > + fprintf(stderr, "Unable to open /dev/sgx_enclave\n");
> > + goto err;
> > + }
> > +
> > + encl->fd = ret;
> > +
> > + if (!encl_map_bin(path, encl))
> > + goto err;
> > +
> > + ehdr = encl->bin;
> > + phdr_tbl = encl->bin + ehdr->e_phoff;
> > +
> > + for (i = 0; i < ehdr->e_phnum; i++) {
> > + Elf64_Phdr *phdr = &phdr_tbl[i];
> > +
> > + if (phdr->p_type == PT_LOAD)
> > + encl->nr_segments++;
> > + }
> > +
> > + encl->segment_tbl = calloc(encl->nr_segments,
> > + sizeof(struct encl_segment));
> > + if (!encl->segment_tbl)
> > + goto err;
> > +
> > + for (i = 0, j = 0; i < ehdr->e_phnum; i++) {
> > + Elf64_Phdr *phdr = &phdr_tbl[i];
> > + unsigned int flags = phdr->p_flags;
> > + struct encl_segment *seg;
> > +
> > + if (phdr->p_type != PT_LOAD)
> > + continue;
> > +
> > + seg = &encl->segment_tbl[j];
> > +
> > + if (!!(flags & ~(PF_R | PF_W | PF_X))) {
> > + fprintf(stderr,
> > + "%d has invalid segment flags 0x%02x.\n", i,
> > + phdr->p_flags);
> > + goto err;
> > + }
> > +
> > + if (j == 0 && flags != (PF_R | PF_W)) {
> > + fprintf(stderr,
> > + "TCS has invalid segment flags 0x%02x.\n",
> > + phdr->p_flags);
> > + goto err;
> > + }
> > +
> > + if (j == 0) {
> > + src_offset = (phdr->p_offset & PAGE_MASK) - src_offset;
> > +
> > + seg->prot = PROT_READ | PROT_WRITE;
> > + seg->flags = SGX_PAGE_TYPE_TCS << 8;
> > + } else {
> > + seg->prot = (phdr->p_flags & PF_R) ? PROT_READ : 0;
> > + seg->prot |= (phdr->p_flags & PF_W) ? PROT_WRITE : 0;
> > + seg->prot |= (phdr->p_flags & PF_X) ? PROT_EXEC : 0;
> > + seg->flags = (SGX_PAGE_TYPE_REG << 8) | seg->prot;
> > + }
> > +
> > + seg->offset = (phdr->p_offset & PAGE_MASK) - src_offset;
> > + seg->size = (phdr->p_filesz + PAGE_SIZE - 1) & PAGE_MASK;
> > +
> > + printf("0x%016lx 0x%016lx 0x%02x\n", seg->offset, seg->size,
> > + seg->prot);
> > +
> > + j++;
> > + }
> > +
> > + assert(j == encl->nr_segments);
> > +
> > + encl->src = encl->bin + src_offset;
> > + encl->src_size = encl->segment_tbl[j - 1].offset +
> > + encl->segment_tbl[j - 1].size;
> > +
> > + for (encl->encl_size = 4096; encl->encl_size < encl->src_size; )
> > + encl->encl_size <<= 1;
>
> Something's fishy. That selftest fails with
>
> mmap: Cannot allocate memory
>
> I sprinkled some printfs at this size computation above and here's what
> it says:
>
> 0x00007fdd3b4ca190 0x0000000000002000 0x03
> 0x00007fdd3b4cc190 0x0000000000001000 0x05
> 0x00007fdd3b4cd190 0x0000000000003000 0x03
> encl_load: encl->nr_segments: 3
> encl_load: seg2 offset: 0x7fdd3b4cd190, seg2 size: 12288
> encl_load: encl_size: 140737488355328, src_size: 140588159402384
> encl_map_area: encl_size: 140737488355328
> mmap: Cannot allocate memory
>
> src_size is computed by adding the offset and size of the last segment
> which is at index 2.

src_size does not look right. I'll debug.

> The loop computes encl_size to 0x0000800000000000 then and mmap tries to
> map double that in encl_map_area(). Looks like too much to me too.

The enclave base must be naturally aligned in relative to its size.

> What's up?
>
> --
> Regards/Gruss,
> Boris.
>
> https://people.kernel.org/tglx/notes-about-netiquette

/Jarkko