[PATCH for_v29 v3 2/2] selftests/sgx: Add selftest to invoke __vsgx_enter_enclave() from C

[Sean Christopherson <sean.j.christopherson@intel.com>]

Add a selftest to call __vsgx_enter_enclave() from C.  Stop clearing
non-volatile registers in the enclave's trampoline code to avoid
clobbering the untrusted runtime's state when the vDSO is called from C.

Suggested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 tools/testing/selftests/sgx/main.c             | 18 +++++++++++++++---
 .../selftests/sgx/test_encl_bootstrap.S        |  6 +-----
 2 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/tools/testing/selftests/sgx/main.c b/tools/testing/selftests/sgx/main.c
index f6bb40f22884..5394b2f6af8e 100644
--- a/tools/testing/selftests/sgx/main.c
+++ b/tools/testing/selftests/sgx/main.c
@@ -19,7 +19,7 @@
 #include "main.h"
 
 static const uint64_t MAGIC = 0x1122334455667788ULL;
-void *eenter;
+vdso_sgx_enter_enclave_t eenter;
 
 struct vdso_symtab {
 	Elf64_Sym *elf_symtab;
@@ -173,15 +173,27 @@ int main(int argc, char *argv[], char *envp[])
 
 	sgx_call_vdso((void *)&MAGIC, &result, 0, EENTER, NULL, NULL,
 		      (void *)encl.encl_base, &exception, NULL);
-	if (result != MAGIC)
+	if (result != MAGIC) {
+		printf("FAIL: sgx_call_vdso(), expected: 0x%lx, got: 0x%lx\n",
+		       MAGIC, result);
 		goto err;
+	}
+
+	/* Invoke the vDSO directly. */
+	result = 0;
+	eenter((unsigned long)&MAGIC, (unsigned long)&result, 0, EENTER, 0, 0,
+	       (void *)encl.encl_base, &exception, NULL);
+	if (result != MAGIC) {
+		printf("FAIL: eenter(), expected: 0x%lx, got: 0x%lx\n",
+		       MAGIC, result);
+		goto err;
+	}
 
 	printf("SUCCESS\n");
 	encl_delete(&encl);
 	exit(0);
 
 err:
-	printf("FAILURE\n");
 	encl_delete(&encl);
 	exit(1);
 }
diff --git a/tools/testing/selftests/sgx/test_encl_bootstrap.S b/tools/testing/selftests/sgx/test_encl_bootstrap.S
index 6a5d734cbf16..6836ea86126e 100644
--- a/tools/testing/selftests/sgx/test_encl_bootstrap.S
+++ b/tools/testing/selftests/sgx/test_encl_bootstrap.S
@@ -54,7 +54,7 @@ encl_entry:
 
 	pop	%rbx # pop the enclave base address
 
-	# Clear GPRs.
+	/* Clear volatile GPRs, except RAX (EEXIT leaf). */
 	xor     %rcx, %rcx
 	xor     %rdx, %rdx
 	xor     %rdi, %rdi
@@ -63,10 +63,6 @@ encl_entry:
 	xor     %r9, %r9
 	xor     %r10, %r10
 	xor     %r11, %r11
-	xor     %r12, %r12
-	xor     %r13, %r13
-	xor     %r14, %r14
-	xor     %r15, %r15
 
 	# Reset status flags.
 	add     %rdx, %rdx # OF = SF = AF = CF = 0; ZF = PF = 1
-- 
2.26.0