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    SubjectRe: [PATCH v36 22/24] selftests/x86: Add a selftest for SGX
    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

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