linux-kernel - [PATCH] selftests/sgx: remove checks for file execute permissions

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Message-Id: <20210621190556.4B5DCBB1@viggo.jf.intel.com>
Date:   Mon, 21 Jun 2021 12:05:56 -0700
From:   Dave Hansen <dave.hansen@...ux.intel.com>
To:     linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        tim.gardner@...onical.com, jarkko@...nel.org,
        reinette.chatre@...el.com, shuah@...nel.org,
        linux-sgx@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: [PATCH] selftests/sgx: remove checks for file execute permissions


The SGX selftests can fail for a bunch of non-obvious reasons
like 'noexec' permissions on /dev (which is the default *EVERYWHERE*
it seems).

A new test mistakenly also looked for +x permission on the
/dev/sgx_enclave.  File execute permissions really only apply to
the ability of execve() to work on a file, *NOT* on the ability
for an application to map the file with PROT_EXEC.  SGX needs to
mmap(PROT_EXEC), but doesn't need to execve() the device file.

Remove the check.

Fixes: 4284f7acb78b ("selftests/sgx: Improve error detection and messages")
Reported-by: Tim Gardner <tim.gardner@...onical.com>
Cc: Jarkko Sakkinen <jarkko@...nel.org>
Cc: Reinette Chatre <reinette.chatre@...el.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Shuah Khan <shuah@...nel.org>
Cc: linux-sgx@...r.kernel.org
Cc: linux-kselftest@...r.kernel.org
Cc: linux-kernel@...r.kernel.org

---

 b/tools/testing/selftests/sgx/load.c |   16 +++-------------
 1 file changed, 3 insertions(+), 13 deletions(-)

diff -puN tools/testing/selftests/sgx/load.c~sgx-no-file-exec tools/testing/selftests/sgx/load.c
--- a/tools/testing/selftests/sgx/load.c~sgx-no-file-exec	2021-06-21 11:48:25.226294281 -0700
+++ b/tools/testing/selftests/sgx/load.c	2021-06-21 12:03:28.023292029 -0700
@@ -150,16 +150,6 @@ bool encl_load(const char *path, struct
 		goto err;
 	}
 
-	/*
-	 * This just checks if the /dev file has these permission
-	 * bits set.  It does not check that the current user is
-	 * the owner or in the owning group.
-	 */
-	if (!(sb.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))) {
-		fprintf(stderr, "no execute permissions on device file %s\n", device_path);
-		goto err;
-	}
-
 	ptr = mmap(NULL, PAGE_SIZE, PROT_READ, MAP_SHARED, fd, 0);
 	if (ptr == (void *)-1) {
 		perror("mmap for read");
@@ -169,13 +159,13 @@ bool encl_load(const char *path, struct
 
 #define ERR_MSG \
 "mmap() succeeded for PROT_READ, but failed for PROT_EXEC.\n" \
-" Check that current user has execute permissions on %s and \n" \
-" that /dev does not have noexec set: mount | grep \"/dev .*noexec\"\n" \
+" Check that /dev does not have noexec set:\n" \
+" \tmount | grep \"/dev .*noexec\"\n" \
 " If so, remount it executable: mount -o remount,exec /dev\n\n"
 
 	ptr = mmap(NULL, PAGE_SIZE, PROT_EXEC, MAP_SHARED, fd, 0);
 	if (ptr == (void *)-1) {
-		fprintf(stderr, ERR_MSG, device_path);
+		fprintf(stderr, ERR_MSG);
 		goto err;
 	}
 	munmap(ptr, PAGE_SIZE);
_