On Thu, Aug 27, 2020 at 08:20:51AM -0700, Sean Christopherson wrote:
> 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;
Updated, thanks.
/Jarkko
