selftests/exec: Add 32 tests for AT_EXECVE_CHECK and exec securebits

Test that checks performed by execveat(..., AT_EXECVE_CHECK) are
consistent with noexec mount points and file execute permissions.

Test that SECBIT_EXEC_RESTRICT_FILE and SECBIT_EXEC_DENY_INTERACTIVE are
inherited by child processes and that they can be pinned with the
appropriate SECBIT_EXEC_RESTRICT_FILE_LOCKED and
SECBIT_EXEC_DENY_INTERACTIVE_LOCKED bits.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Paul Moore <paul@paul-moore.com>
Cc: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Link: https://lore.kernel.org/r/20241212174223.389435-4-mic@digikod.net
Signed-off-by: Kees Cook <kees@kernel.org>

tools/testing/selftests/exec/.gitignore

@@ -9,6 +9,8 @@ execveat.ephemeral
 execveat.denatured
 non-regular
 null-argv
+/check-exec
+/false
 /load_address.*
 !load_address.c
 /recursion-depth

tools/testing/selftests/exec/Makefile

@@ -1,6 +1,9 @@
 # SPDX-License-Identifier: GPL-2.0
 CFLAGS = -Wall
 CFLAGS += -Wno-nonnull
+CFLAGS += $(KHDR_INCLUDES)
+
+LDLIBS += -lcap
 
 ALIGNS := 0x1000 0x200000 0x1000000
 ALIGN_PIES        := $(patsubst %,load_address.%,$(ALIGNS))
@@ -9,12 +12,14 @@ ALIGNMENT_TESTS   := $(ALIGN_PIES) $(ALIGN_STATIC_PIES)
 
 TEST_PROGS := binfmt_script.py
 TEST_GEN_PROGS := execveat non-regular $(ALIGNMENT_TESTS)
+TEST_GEN_PROGS_EXTENDED := false
 TEST_GEN_FILES := execveat.symlink execveat.denatured script subdir
 # Makefile is a run-time dependency, since it's accessed by the execveat test
 TEST_FILES := Makefile
 
 TEST_GEN_PROGS += recursion-depth
 TEST_GEN_PROGS += null-argv
+TEST_GEN_PROGS += check-exec
 
 EXTRA_CLEAN := $(OUTPUT)/subdir.moved $(OUTPUT)/execveat.moved $(OUTPUT)/xxxxx*	\
 	       $(OUTPUT)/S_I*.test
@@ -38,3 +43,5 @@ $(OUTPUT)/load_address.0x%: load_address.c
 $(OUTPUT)/load_address.static.0x%: load_address.c
 	$(CC) $(CFLAGS) $(LDFLAGS) -Wl,-z,max-page-size=$(lastword $(subst ., ,$@)) \
 		-fPIE -static-pie $< -o $@
+$(OUTPUT)/false: false.c
+	$(CC) $(CFLAGS) $(LDFLAGS) -static $< -o $@