On Thu, Aug 27, 2020 at 12:47:04AM -0400, Nathaniel McCallum wrote: > > +int main(int argc, char *argv[], char *envp[]) > > +{ > > + struct sgx_enclave_exception exception; > > + struct vdso_symtab symtab; > > + Elf64_Sym *eenter_sym; > > + uint64_t result = 0; > > + struct encl encl; > > + unsigned int i; > > + void *addr; > > + > > + if (!encl_load("test_encl.elf", &encl)) > > + goto err; > > + > > + if (!encl_measure(&encl)) > > + goto err; > > + > > + if (!encl_build(&encl)) > > + goto err; > > + > > + /* > > + * An enclave consumer only must do this. > > + */ > > + for (i = 0; i < encl.nr_segments; i++) { > > + struct encl_segment *seg = &encl.segment_tbl[i]; > > + > > + addr = mmap((void *)encl.encl_base + seg->offset, seg->size, > > + seg->prot, MAP_SHARED | MAP_FIXED, encl.fd, 0); > > My patch version is a bit behind (v32), but I suspect this still > applies. I discovered the following by accident. > > In the Enarx code base, this invocation succeeds: > mmap(0x200000000000, 0x1000, PROT_READ | PROT_WRITE, MAP_SHARED | > MAP_FIXED, sgxfd, 0) > > However, this one fails with -EINVAL: > mmap(0x200000000000, 0x1000, PROT_READ | PROT_WRITE, > MAP_SHARED_VALIDATE | MAP_FIXED, sgxfd, 0) > > From man mmap: > > MAP_SHARED_VALIDATE (since Linux 4.15) > This flag provides the same behavior as MAP_SHARED > except that MAP_SHARED mappings ignore unknown > flags in flags. By contrast, when creating a mapping > using MAP_SHARED_VALIDATE, the kernel veri‐ > fies all passed flags are known and fails the > mapping with the error EOPNOTSUPP for unknown > flags. This mapping type is also required to be able to > use some mapping flags (e.g., MAP_SYNC). > > I can try again on a newer patch set tomorrow if need be. But the > documentation of mmap() doesn't match the behavior I'm seeing. A brief > look through the patch set didn't turn up anything obvious that could > be causing this.
This is a bug in sgx_get_unmapped_area(). EPC must be mapped SHARED, and so MAP_PRIVATE is disallowed. The current check is: if (flags & MAP_PRIVATE) return -EINVAL; and the base "flags" are: #define MAP_SHARED 0x01 /* Share changes */ #define MAP_PRIVATE 0x02 /* Changes are private */ #define MAP_SHARED_VALIDATE 0x03 /* share + validate extension flags */ which causes the SGX check to interpret MAP_SHARED_VALIDATE as MAP_PRIVATE. The types are just that, types, not flag modifiers. So the SGX code needs to be: if ((flags & MAP_TYPE) == MAP_PRIVATE) return -EINVAL; or unsigned long map_type = (flags & MAP_TYPE); if (map_type != MAP_SHARED && map_type != MAP_SHARED_VALIDATE) return -EINVAL; Side topic, there is at least one existing bug of this nature, in mm/nommu.c. I'll send a patch for that and look for any other instances of the bad pattern.