selftests/sgx: Remove incomplete ABI sanitization code in test enclave

JIRA: https://issues.redhat.com/browse/RHEL-22826
Upstream Status: merged into the linux.git

commit 886c5be
Author: Jo Van Bulck <jo.vanbulck@cs.kuleuven.be>
Date:   Thu Oct 5 17:38:54 2023 +0200

    selftests/sgx: Remove incomplete ABI sanitization code in test enclave

    As the selftest enclave is *not* intended for production, simplify the
    code by not initializing CPU configuration registers as expected by the
    ABI on enclave entry or cleansing caller-save registers on enclave exit.

    Signed-off-by: Jo Van Bulck <jo.vanbulck@cs.kuleuven.be>
    Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
    Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
    Link: https://lore.kernel.org/all/da0cfb1e-e347-f7f2-ac72-aec0ee0d867d@intel.com/
    Link: https://lore.kernel.org/all/20231005153854.25566-14-jo.vanbulck%40cs.kuleuven.be

Signed-off-by: Vladis Dronov <vdronov@redhat.com>

Author: nefigtut

tools/testing/selftests/sgx/test_encl_bootstrap.S

@@ -59,21 +59,11 @@ encl_entry_core:
 
 	push	%rcx # push the address after EENTER
 
+	# NOTE: as the selftest enclave is *not* intended for production,
+	# simplify the code by not initializing ABI registers on entry or
+	# cleansing caller-save registers on exit.
 	call	encl_body
 
-	/* Clear volatile GPRs, except RAX (EEXIT function). */
-	xor     %rcx, %rcx
-	xor     %rdx, %rdx
-	xor     %rdi, %rdi
-	xor     %rsi, %rsi
-	xor     %r8, %r8
-	xor     %r9, %r9
-	xor     %r10, %r10
-	xor     %r11, %r11
-
-	# Reset status flags.
-	add     %rdx, %rdx # OF = SF = AF = CF = 0; ZF = PF = 1
-
 	# Prepare EEXIT target by popping the address of the instruction after
 	# EENTER to RBX.
 	pop	%rbx