[PATCH v3 11/11] kselftest: arm64: fake_sigreturn_misaligned_sp

[Cristian Marussi <cristian.marussi@arm.com>]

Added a simple fake_sigreturn testcase which places a valid
sigframe on a non-16 bytes aligned SP.
fake_sigretrun() helper function has been patched accordingly
to support placing a sigframe on a non-16 bytes aligned address.
Expects a SIGSEGV on test PASS.

Adds also a test TODO lists holding some further test ideas.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
---
Re-added this text after fixing the forced misaglinment procedure in
fake_sigreturn() itself: require a ZERO alignment and you'll get
your sigframe placed on a misaligned SP (2-bytes off the 16-align)
---
 .../testing/selftests/arm64/signal/signals.S  | 21 +++++++++----
 .../arm64/signal/testcases/TODO.readme        |  8 +++++
 .../testcases/fake_sigreturn_misaligned_sp.c  | 30 +++++++++++++++++++
 3 files changed, 53 insertions(+), 6 deletions(-)
 create mode 100644 tools/testing/selftests/arm64/signal/testcases/TODO.readme
 create mode 100644 tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_misaligned_sp.c

diff --git a/tools/testing/selftests/arm64/signal/signals.S b/tools/testing/selftests/arm64/signal/signals.S
index 6262b877400b..2099871176ed 100644
--- a/tools/testing/selftests/arm64/signal/signals.S
+++ b/tools/testing/selftests/arm64/signal/signals.S
@@ -13,19 +13,28 @@ call_fmt:
 
 .globl fake_sigreturn
 
-/*	fake_sigreturn	x0:&sigframe,  x1:sigframe_size,  x2:alignment_SP */
+/*	fake_sigreturn	x0:&sigframe, x1:sigframe_sz, x2:align */
 fake_sigreturn:
-	mov x20, x0
-	mov x21, x1
-	mov x22, x2
-	mov x23, sp
 
-	/* create space on the stack for fake sigframe..."x22"-aligned */
+	/* Save args and decide which aligment to enforce */
+	mov 	x23, sp
+	mov	x20, x0
+	mov 	x21, x1
+	/* x22 and x24 used for forcing alignment or misalignment */
+	mov	x22, x2
+	mov	x24, #0
+	cbnz	x22, 1f
+	mov	x22, #16
+	mov	x24, #2
+
+1:	/* create space on the stack for fake sigframe..."x22"-aligned */
 	mov x0, #0
 	add x0, x21, x22
 	sub x22, x22, #1
 	bic x0, x0, x22
 	sub x23, x23, x0
+	/* force misaligned by x24 bytes if required alignment was zero */
+	add x23, x23, x24
 
 	ldr x0, =call_fmt
 	mov x1, x21
diff --git a/tools/testing/selftests/arm64/signal/testcases/TODO.readme b/tools/testing/selftests/arm64/signal/testcases/TODO.readme
new file mode 100644
index 000000000000..5c949492e7ab
--- /dev/null
+++ b/tools/testing/selftests/arm64/signal/testcases/TODO.readme
@@ -0,0 +1,8 @@
+Some more possible ideas for signals tests:
+
+- fake_sigreturn_unmapped_sp
+- fake_sigreturn_kernelspace_sp
+- fake_sigreturn_sve_bad_extra_context
+- mangle_sve_invalid_extra_context
+- mangle_pstate_invalid_el for H modes (+ macroization ?)
+- fake_sigreturn_overflow_reserved
diff --git a/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_misaligned_sp.c b/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_misaligned_sp.c
new file mode 100644
index 000000000000..3ee8c500c7d1
--- /dev/null
+++ b/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_misaligned_sp.c
@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (C) 2019 ARM Limited */
+
+#include <ucontext.h>
+
+#include "test_signals_utils.h"
+#include "testcases.h"
+
+struct fake_sigframe sf;
+
+static int fake_sigreturn_misaligned_run(struct tdescr *td,
+				         siginfo_t *si, ucontext_t *uc)
+{
+	/* just to fill the ucontext_t with something real */
+	if (!get_current_context(td, &sf.uc))
+		return 1;
+
+	/* Forcing sigframe on misaligned (=!16) SP */
+	fake_sigreturn(&sf, sizeof(sf), 0);
+
+	return 1;
+}
+
+struct tdescr tde = {
+		.name = "FAKE_SIGRETURN_MISALIGNED_SP",
+		.descr = "Triggers a fake sigreturn with a misaligned sigframe on SP",
+		.sig_ok = SIGSEGV,
+		.timeout = 3,
+		.run = fake_sigreturn_misaligned_run,
+};
-- 
2.17.1