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

Borislav Petkov
2020-11-17T17:27:19Z

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.

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.

What's up?

--
Regards/Gruss,
Boris.