Re: [PATCH 1/4] selftests/sgx: Fix segfault upon early test failure

[Jarkko Sakkinen <jarkko@kernel.org>]

On Fri, Jan 28, 2022 at 10:23:56AM -0800, Reinette Chatre wrote:
> A segfault is encountered if there happens to be an
> early failure of any of the SGX tests. One way to
> reproduce this is to remove the enclave binary
> "test_encl.elf" that will trigger early enclave loading
> failure followed by a segfault.
> 
> The segfault occurs within encl_delete() that cleans up
> after an enclave by umapping its mapped regions and closing
> the file descriptor to the SGX driver. As integrated with
> the kselftest harness encl_delete() is called upon exit
> from every test, irrespective of test success. encl_delete()
> is also called to clean up if an error is encountered during
> enclave loading.
> 
> encl_delete() is thus responsible for cleaning any amount of
> enclave state - including state that has already been cleaned.
> 
> encl_delete() starts by accessing encl->segment_tbl that may
> not have been created yet due to a very early failure or may
> already be cleaned up because of a failure encountered after
> encl->segment_tbl was created.
> 
> Ensure encl->segment_tbl is valid before attempting to access
> memory offset from it. The offset with which it is accessed,
> encl->nr_segments, is initialized after encl->segment_tbl and
> thus considered valid to use after the encl->segment_tbl check
> succeeds.

Nit: textwidth=75

Not something I would NAK but just saying.

> 
> Fixes: 3200505d4de6 ("selftests/sgx: Create a heap for the test enclave")
> Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
> ---
>  tools/testing/selftests/sgx/load.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/testing/selftests/sgx/load.c b/tools/testing/selftests/sgx/load.c
> index 9d4322c946e2..006b464c8fc9 100644
> --- a/tools/testing/selftests/sgx/load.c
> +++ b/tools/testing/selftests/sgx/load.c
> @@ -21,7 +21,7 @@
>  
>  void encl_delete(struct encl *encl)
>  {
> -	struct encl_segment *heap_seg = &encl->segment_tbl[encl->nr_segments - 1];
> +	struct encl_segment *heap_seg;
>  
>  	if (encl->encl_base)
>  		munmap((void *)encl->encl_base, encl->encl_size);
> @@ -32,10 +32,11 @@ void encl_delete(struct encl *encl)
>  	if (encl->fd)
>  		close(encl->fd);
>  
> -	munmap(heap_seg->src, heap_seg->size);
> -
> -	if (encl->segment_tbl)
> +	if (encl->segment_tbl) {
> +		heap_seg = &encl->segment_tbl[encl->nr_segments - 1];
> +		munmap(heap_seg->src, heap_seg->size);
>  		free(encl->segment_tbl);
> +	}
>  
>  	memset(encl, 0, sizeof(*encl));
>  }
> -- 
> 2.25.1
> 

Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Tested-by: Jarkko Sakkinen <jarkko@kernel.org> 

I tested this by a minor code mod to trigger to failure case.

/Jarkko