app: create dedicated selftest directory

This directory contains bare-metal applications designed to test various
functionalities provided by `libsgxstep` without the need for SGX enclaves.

Also add some documentation cf #48

.github/workflows/ci.yaml

@@ -50,4 +50,5 @@ jobs:
       - name: Build SGX-Step sample applications
         run: |
           source /opt/intel/sgxsdk/environment
+          for d in $GITHUB_WORKSPACE/app/selftest/*/ ; do echo -e "\n**** $d ****\n" ; cd "$d" ; make ; ldd ./app ; done
           for d in $GITHUB_WORKSPACE/app/*/ ; do echo -e "\n**** $d ****\n" ; cd "$d" ; make ; ldd ./app ; done

README.md

@@ -242,7 +242,7 @@ the example applications in the "app" directory.
 First, check the APIC and interrupt-descriptor table setup:
 
 ```bash
-$ cd app/idt
+$ cd app/selftest/idt
 $ make run    # fires interrupts in an infinite loop to stress-test stability; exit with CTRL-C
 ```
 
@@ -282,7 +282,7 @@ access rights on specific code or data pages of interest.
 
 **Note (timer interval).** The exact timer interval value depends on CPU
 frequency, and hence remains inherently platform-specific (see also
-[app/apic](app/apic) for detailed microbenchmarks assessing the accuracy of
+[app/selftest/apic](app/selftest/apic) for detailed microbenchmarks assessing the accuracy of
 various APIC timer modes). Configure a suitable value in `/app/bench/main.c`.
 We established precise timer intervals for our evaluation platforms (see table
 below) by tweaking and observing the NOP microbenchmark enclave instruction

app/selftest/README.md

@@ -0,0 +1,31 @@
+# SGX-Step "Selftest" Applications
+
+This directory contains bare-metal applications designed to test various functionalities provided by `libsgxstep` without the need for SGX enclaves.
+
+## Directory Overview
+
+| Directory  | Description                                                                                               |
+|------------|-----------------------------------------------------------------------------------------------------------|
+| `apic`     | Microbenchmarks for timer interrupts via various Advanced Programmable Interrupt Controller (APIC) modes. |
+| `apic-ipi` | Microbenchmarks for APIC inter-processor interrupts.                                                      |
+| `cpl`      | Changing the Current Privilege Level (CPL) through calland interrupt GDT/IDT gates.                       |
+| `idt`      | Custom handlers for software and timer interrupts via the Interrupt Descriptor Table (IDT).               |
+| `idt_isr_map` | Stresstest to demonstrate custom IDT handlers can be called across processes.                          |
+
+## Usage
+
+To run the selftest applications:
+
+1. Navigate to the desired directory.
+2. Compile the application:
+   ```bash
+   make
+   ```
+3. Run the application with:
+   ```bash
+   sudo ./app
+   ```
+
+Reference output is available in the respective README files within each subdirectory.
+
+**Note:** Any crashes during execution may indicate that your machine is not set up correctly for using SGX-Step. 

app/apic-ipi/Makefile → app/selftest/apic-ipi/Makefile

@@ -1,4 +1,4 @@
-LIBSGXSTEP_DIR       = ../..
+LIBSGXSTEP_DIR       = ../../..
 LIBSGXSTEP           = $(LIBSGXSTEP_DIR)/libsgxstep
 -include $(LIBSGXSTEP)/Makefile.config
 

app/apic/Makefile → app/selftest/apic/Makefile

@@ -1,4 +1,4 @@
-LIBSGXSTEP_DIR       = ../..
+LIBSGXSTEP_DIR       = ../../..
 LIBSGXSTEP           = $(LIBSGXSTEP_DIR)/libsgxstep
 -include $(LIBSGXSTEP)/Makefile.config
 

app/cpl/Makefile → app/selftest/cpl/Makefile

@@ -1,4 +1,4 @@
-LIBSGXSTEP_DIR       = ../..
+LIBSGXSTEP_DIR       = ../../..
 LIBSGXSTEP           = $(LIBSGXSTEP_DIR)/libsgxstep
 -include $(LIBSGXSTEP)/Makefile.config
 

app/idt_isr_map/Makefile → app/selftest/idt/Makefile

@@ -1,4 +1,4 @@
-LIBSGXSTEP_DIR       = ../..
+LIBSGXSTEP_DIR       = ../../..
 LIBSGXSTEP           = $(LIBSGXSTEP_DIR)/libsgxstep
 -include $(LIBSGXSTEP)/Makefile.config
 

app/idt/main.c → app/selftest/idt/main.c

@@ -28,7 +28,7 @@
 #define DO_APIC_SW_IRQ              1
 #define DO_APIC_TMR_IRQ             1
 #define DO_EXEC_PRIV                1
-#define NUM                         100
+#define NUM                         10
 #define INFINITE_LOOP               1
 #define NEMESIS_HIGH                1
 

app/idt/Makefile → app/selftest/idt_isr_map/Makefile

@@ -1,4 +1,4 @@
-LIBSGXSTEP_DIR       = ../..
+LIBSGXSTEP_DIR       = ../../..
 LIBSGXSTEP           = $(LIBSGXSTEP_DIR)/libsgxstep
 -include $(LIBSGXSTEP)/Makefile.config
 

libsgxstep/Makefile.config

@@ -23,4 +23,5 @@ ifndef LIBSGXSTEP_SILENT
    export LIBSGXSTEP_SILENT=0
 endif
 
+LDFLAGS             += -z noexecstack
 CFLAGS              += -DSGX_STEP_PLATFORM=$(SGX_STEP_PLATFORM) -DNO_SGX=$(NO_SGX) -DLIBSGXSTEP_SILENT=$(LIBSGXSTEP_SILENT)