[tip: x86/asm] selftests/kexec: Add x86_64 selftest for kexec-jump and exception handling

[tip-bot2 for David Woodhouse]

The following commit has been merged into the x86/asm branch of tip:

Commit-ID:     7615b94b6371dab5d7d8c1ca4f95ed3f866e1c51
Gitweb:        https://git.kernel.org/tip/7615b94b6371dab5d7d8c1ca4f95ed3f866e1c51
Author:        David Woodhouse <dwmw@xxxxxxxxxxxx>
AuthorDate:    Wed, 26 Mar 2025 14:16:04 
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Thu, 10 Apr 2025 12:17:14 +02:00

selftests/kexec: Add x86_64 selftest for kexec-jump and exception handling

Add a self test which exercises both the kexec-jump facility, and the
kexec exception handling.

Invoke a trivial payload which just does an int3 and returns,
flip-flopping its entry point for the next invocation between two
implementations of the same thing.

Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Ard Biesheuvel <ardb@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20250326142404.256980-5-dwmw2@xxxxxxxxxxxxx
---
 tools/testing/selftests/kexec/Makefile           |  7 +-
 tools/testing/selftests/kexec/test_kexec_jump.c  | 72 +++++++++++++++-
 tools/testing/selftests/kexec/test_kexec_jump.sh | 42 +++++++++-
 3 files changed, 121 insertions(+)
 create mode 100644 tools/testing/selftests/kexec/test_kexec_jump.c
 create mode 100755 tools/testing/selftests/kexec/test_kexec_jump.sh

diff --git a/tools/testing/selftests/kexec/Makefile b/tools/testing/selftests/kexec/Makefile
index 67fe7a4..e3000cc 100644
--- a/tools/testing/selftests/kexec/Makefile
+++ b/tools/testing/selftests/kexec/Makefile
@@ -8,6 +8,13 @@ ifeq ($(ARCH_PROCESSED),$(filter $(ARCH_PROCESSED),x86 ppc64le))
 TEST_PROGS := test_kexec_load.sh test_kexec_file_load.sh
 TEST_FILES := kexec_common_lib.sh
 
+include ../../../scripts/Makefile.arch
+
+ifeq ($(IS_64_BIT)$(ARCH_PROCESSED),1x86)
+TEST_PROGS += test_kexec_jump.sh
+test_kexec_jump.sh: $(OUTPUT)/test_kexec_jump
+endif
+
 include ../lib.mk
 
 endif
diff --git a/tools/testing/selftests/kexec/test_kexec_jump.c b/tools/testing/selftests/kexec/test_kexec_jump.c
new file mode 100644
index 0000000..fbce287
--- /dev/null
+++ b/tools/testing/selftests/kexec/test_kexec_jump.c
@@ -0,0 +1,72 @@
+#include <unistd.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <linux/kexec.h>
+#include <linux/reboot.h>
+#include <sys/reboot.h>
+#include <sys/syscall.h>
+
+asm(
+    "  .code64\n"
+    "  .data\n"
+    "purgatory_start:\n"
+
+    // Trigger kexec debug exception handling
+    "  int3\n"
+
+    // Set load address for next time
+    "  leaq purgatory_start_b(%rip), %r11\n"
+    "  movq %r11, 8(%rsp)\n"
+
+    // Back to Linux
+    "  ret\n"
+
+    // Same again
+    "purgatory_start_b:\n"
+
+    // Trigger kexec debug exception handling
+    "  int3\n"
+
+    // Set load address for next time
+    "  leaq purgatory_start(%rip), %r11\n"
+    "  movq %r11, 8(%rsp)\n"
+
+    // Back to Linux
+    "  ret\n"
+
+    "purgatory_end:\n"
+    ".previous"
+);
+extern char purgatory_start[], purgatory_end[];
+
+int main (void)
+{
+        struct kexec_segment segment = {};
+	int ret;
+
+	segment.buf = purgatory_start;
+	segment.bufsz = purgatory_end - purgatory_start;
+	segment.mem = (void *)0x400000;
+	segment.memsz = 0x1000;
+	ret = syscall(__NR_kexec_load, 0x400000, 1, &segment, KEXEC_PRESERVE_CONTEXT);
+	if (ret) {
+		perror("kexec_load");
+		exit(1);
+	}
+
+	ret = syscall(__NR_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, LINUX_REBOOT_CMD_KEXEC);
+	if (ret) {
+		perror("kexec reboot");
+		exit(1);
+	}
+
+	ret = syscall(__NR_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, LINUX_REBOOT_CMD_KEXEC);
+	if (ret) {
+		perror("kexec reboot");
+		exit(1);
+	}
+	printf("Success\n");
+	return 0;
+}
+
diff --git a/tools/testing/selftests/kexec/test_kexec_jump.sh b/tools/testing/selftests/kexec/test_kexec_jump.sh
new file mode 100755
index 0000000..6ae9770
--- /dev/null
+++ b/tools/testing/selftests/kexec/test_kexec_jump.sh
@@ -0,0 +1,42 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+#
+# Prevent loading a kernel image via the kexec_load syscall when
+# signatures are required.  (Dependent on CONFIG_IMA_ARCH_POLICY.)
+
+TEST="$0"
+. ./kexec_common_lib.sh
+
+# kexec requires root privileges
+require_root_privileges
+
+# get the kernel config
+get_kconfig
+
+kconfig_enabled "CONFIG_KEXEC_JUMP=y" "kexec_jump is enabled"
+if [ $? -eq 0 ]; then
+	log_skip "kexec_jump is not enabled"
+fi
+
+kconfig_enabled "CONFIG_IMA_APPRAISE=y" "IMA enabled"
+ima_appraise=$?
+
+kconfig_enabled "CONFIG_IMA_ARCH_POLICY=y" \
+	"IMA architecture specific policy enabled"
+arch_policy=$?
+
+get_secureboot_mode
+secureboot=$?
+
+if [ $secureboot -eq 1 ] && [ $arch_policy -eq 1 ]; then
+    log_skip "Secure boot and CONFIG_IMA_ARCH_POLICY are enabled"
+fi
+
+./test_kexec_jump
+if [ $? -eq 0 ]; then
+    log_pass "kexec_jump succeeded"
+else
+    # The more likely failure mode if anything went wrong is that the
+    # kernel just crashes. But if we get back here, sure, whine anyway.
+    log_fail "kexec_jump failed"
+fi