[PAL] Allow to validate entrypoint ELF file separately

[dimakuv]

Description of the changes

Previously, the entrypoint ELF file (loader.entrypoint in manifest) contents were validated during file read and file mmap, just like with all other files. In particular, Linux-SGX PAL expects the entrypoint to be marked as sgx.trusted_files and validates its SHA256 hash during file read/mmap.

However, future commits will move handling of sgx.trusted_files to the LibOS layer. Thus, file read/mmap at the PAL layer will lose validation guarantees. This commit introduces a separate loader.entrypoint_sha256 manifest option and a corresponding logic to validate the (only required) entrypoint file. A new assumption is made now, that the only file to be loaded by PAL (and not by LibOS) is this entrypoint file; this assumption can be made because the entrypoint has no dependencies.

Extracted from #1812.

Related to #1716 (ideally both should be merged one after another).

How to test this PR?

CI is enough.

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This change is 

[dimakuv]

Reviewable status: 0 of 6 files reviewed, all discussions resolved, not enough approvals from maintainers (2 more required), not enough approvals from different teams (1 more required, approved so far: Intel)

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-- commits line 16 at r1:
Please note that this assumption is already enforced by our PAL code:

gramine/pal/src/pal_rtld.c

Lines 261 to 269 in e3d3aa3

	case DT_NEEDED:
	if (needed_offset_found) {
	log_error("Loaded binary has more than one dependency (must be only one "
	"dependency -- the PAL binary)");
	return -PAL_ERROR_DENIED;
	}
	needed_offset = dynamic_section_entry->d_un.d_val;
	needed_offset_found = true;
	break;

[dimakuv]

Reviewable status: 0 of 6 files reviewed, 2 unresolved discussions, not enough approvals from maintainers (2 more required), not enough approvals from different teams (1 more required, approved so far: Intel) (waiting on @dimakuv)

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pal/src/host/linux-sgx/pal_misc.c line 22 at r1 (raw file):

#include "pal_linux_error.h"
#include "seqlock.h"
#include "sgx_arch.h"

TODO: Get rid of sgx_arch.h and sgx_file_hash_t

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pal/src/host/linux-sgx/pal_misc.c line 834 at r1 (raw file):

    }

    if (!entrypoint_sha256_str || strlen(entrypoint_sha256_str) != sizeof(sgx_file_hash_t) * 2) {

TODO: The first clause was already checked above, remove

[dimakuv]

Reviewable status: 0 of 6 files reviewed, all discussions resolved, not enough approvals from maintainers (2 more required), not enough approvals from different teams (1 more required, approved so far: Intel), "fixup! " found in commit messages' one-liners

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pal/src/host/linux-sgx/pal_misc.c line 22 at r1 (raw file):

Previously, dimakuv (Dmitrii Kuvaiskii) wrote…

TODO: Get rid of sgx_arch.h and sgx_file_hash_t

Done

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pal/src/host/linux-sgx/pal_misc.c line 834 at r1 (raw file):

Previously, dimakuv (Dmitrii Kuvaiskii) wrote…

TODO: The first clause was already checked above, remove

Done

[mkow]

Reviewed 5 of 6 files at r1, 1 of 1 files at r2, all commit messages.
Reviewable status: all files reviewed, 6 unresolved discussions, not enough approvals from maintainers (1 more required), not enough approvals from different teams (1 more required, approved so far: Intel), "fixup! " found in commit messages' one-liners (waiting on @dimakuv)

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-- commits line 2 at r2:
that's not optional, which "allow" implies

Suggestion:

[PAL] Validate entrypoint ELF file separately

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pal/src/pal_rtld.c line 659 at r2 (raw file):

    ret = _PalStreamAttributesQueryByHandle(handle, &attr);
    if (ret < 0) {
        log_error("Getting size of ELF file failed");

Suggestion:

log_error("Getting size of loader entrypoint binary failed");

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pal/src/pal_rtld.c line 665 at r2 (raw file):

    buf = malloc(attr.pending_size);
    if (!buf) {
        log_error("Allocating buffer to hold ELF file of size %lu failed", attr.pending_size);

ditto - missing context which ELF file
actually, same for a few other places below

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pal/src/pal_rtld.c line 672 at r2 (raw file):

    size_t remaining = attr.pending_size;
    while (remaining > 0) {
        int64_t read = _PalStreamRead(handle, buf_offset, remaining, buf + buf_offset);

Everything here is wrong ;) ret vs read

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pal/src/host/linux-sgx/pal_misc.c line 832 at r2 (raw file):

        log_error("Cannot find 'loader.entrypoint_sha256' in manifest");
        ret = -PAL_ERROR_INVAL;
        goto out;

Suggestion:

        return -PAL_ERROR_INVAL;

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python/graminelibos/manifest.py line 304 at r2 (raw file):

        if not 'entrypoint_sha256' in loader:
            entrypoint_tf = TrustedFile.from_realpath(uri2path(loader['entrypoint'])).ensure_hash()
            loader.setdefault('entrypoint_sha256', entrypoint_tf.sha256);

Suggestion:

loader['entrypoint_sha256'] = entrypoint_tf.sha256