ARM: kprobes: Add decoding table test coverage analysis

This is used to verify that all combinations of CPU instructions
described by the kprobes decoding tables have a test case.

Signed-off-by: Jon Medhurst <tixy@yxit.co.uk>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>

diff --git a/arch/arm/kernel/kprobes-test.c b/arch/arm/kernel/kprobes-test.c
index 6c0946c023f86a98b00d07f9aa7ac722beb699b6..fe169e934d4250c6045e4bce78c0fcfcfb4b20e8 100644 (file)
--- a/arch/arm/kernel/kprobes-test.c
+++ b/arch/arm/kernel/kprobes-test.c
@@ -178,6 +178,7 @@
 
 #include <linux/kernel.h>
 #include <linux/module.h>
+#include <linux/slab.h>
 #include <linux/kprobes.h>
 
 #include "kprobes.h"
@@ -528,6 +529,250 @@ static int table_test(const union decode_item *table)
 }
 
 
+/*
+ * Decoding table test coverage analysis
+ *
+ * coverage_start() builds a coverage_table which contains a list of
+ * coverage_entry's to match each entry in the specified kprobes instruction
+ * decoding table.
+ *
+ * When test cases are run, coverage_add() is called to process each case.
+ * This looks up the corresponding entry in the coverage_table and sets it as
+ * being matched, as well as clearing the regs flag appropriate for the test.
+ *
+ * After all test cases have been run, coverage_end() is called to check that
+ * all entries in coverage_table have been matched and that all regs flags are
+ * cleared. I.e. that all possible combinations of instructions described by
+ * the kprobes decoding tables have had a test case executed for them.
+ */
+
+bool coverage_fail;
+
+#define MAX_COVERAGE_ENTRIES 256
+
+struct coverage_entry {
+       const struct decode_header      *header;
+       unsigned                        regs;
+       unsigned                        nesting;
+       char                            matched;
+};
+
+struct coverage_table {
+       struct coverage_entry   *base;
+       unsigned                num_entries;
+       unsigned                nesting;
+};
+
+struct coverage_table coverage;
+
+#define COVERAGE_ANY_REG       (1<<0)
+#define COVERAGE_SP            (1<<1)
+#define COVERAGE_PC            (1<<2)
+#define COVERAGE_PCWB          (1<<3)
+
+static const char coverage_register_lookup[16] = {
+       [REG_TYPE_ANY]          = COVERAGE_ANY_REG | COVERAGE_SP | COVERAGE_PC,
+       [REG_TYPE_SAMEAS16]     = COVERAGE_ANY_REG,
+       [REG_TYPE_SP]           = COVERAGE_SP,
+       [REG_TYPE_PC]           = COVERAGE_PC,
+       [REG_TYPE_NOSP]         = COVERAGE_ANY_REG | COVERAGE_SP,
+       [REG_TYPE_NOSPPC]       = COVERAGE_ANY_REG | COVERAGE_SP | COVERAGE_PC,
+       [REG_TYPE_NOPC]         = COVERAGE_ANY_REG | COVERAGE_PC,
+       [REG_TYPE_NOPCWB]       = COVERAGE_ANY_REG | COVERAGE_PC | COVERAGE_PCWB,
+       [REG_TYPE_NOPCX]        = COVERAGE_ANY_REG,
+       [REG_TYPE_NOSPPCX]      = COVERAGE_ANY_REG | COVERAGE_SP,
+};
+
+unsigned coverage_start_registers(const struct decode_header *h)
+{
+       unsigned regs = 0;
+       int i;
+       for (i = 0; i < 20; i += 4) {
+               int r = (h->type_regs.bits >> (DECODE_TYPE_BITS + i)) & 0xf;
+               regs |= coverage_register_lookup[r] << i;
+       }
+       return regs;
+}
+
+static int coverage_start_fn(const struct decode_header *h, void *args)
+{
+       struct coverage_table *coverage = (struct coverage_table *)args;
+       enum decode_type type = h->type_regs.bits & DECODE_TYPE_MASK;
+       struct coverage_entry *entry = coverage->base + coverage->num_entries;
+
+       if (coverage->num_entries == MAX_COVERAGE_ENTRIES - 1) {
+               pr_err("FAIL: Out of space for test coverage data");
+               return -ENOMEM;
+       }
+
+       ++coverage->num_entries;
+
+       entry->header = h;
+       entry->regs = coverage_start_registers(h);
+       entry->nesting = coverage->nesting;
+       entry->matched = false;
+
+       if (type == DECODE_TYPE_TABLE) {
+               struct decode_table *d = (struct decode_table *)h;
+               int ret;
+               ++coverage->nesting;
+               ret = table_iter(d->table.table, coverage_start_fn, coverage);
+               --coverage->nesting;
+               return ret;
+       }
+
+       return 0;
+}
+
+static int coverage_start(const union decode_item *table)
+{
+       coverage.base = kmalloc(MAX_COVERAGE_ENTRIES *
+                               sizeof(struct coverage_entry), GFP_KERNEL);
+       coverage.num_entries = 0;
+       coverage.nesting = 0;
+       return table_iter(table, coverage_start_fn, &coverage);
+}
+
+static void
+coverage_add_registers(struct coverage_entry *entry, kprobe_opcode_t insn)
+{
+       int regs = entry->header->type_regs.bits >> DECODE_TYPE_BITS;
+       int i;
+       for (i = 0; i < 20; i += 4) {
+               enum decode_reg_type reg_type = (regs >> i) & 0xf;
+               int reg = (insn >> i) & 0xf;
+               int flag;
+
+               if (!reg_type)
+                       continue;
+
+               if (reg == 13)
+                       flag = COVERAGE_SP;
+               else if (reg == 15)
+                       flag = COVERAGE_PC;
+               else
+                       flag = COVERAGE_ANY_REG;
+               entry->regs &= ~(flag << i);
+
+               switch (reg_type) {
+
+               case REG_TYPE_NONE:
+               case REG_TYPE_ANY:
+               case REG_TYPE_SAMEAS16:
+                       break;
+
+               case REG_TYPE_SP:
+                       if (reg != 13)
+                               return;
+                       break;
+
+               case REG_TYPE_PC:
+                       if (reg != 15)
+                               return;
+                       break;
+
+               case REG_TYPE_NOSP:
+                       if (reg == 13)
+                               return;
+                       break;
+
+               case REG_TYPE_NOSPPC:
+               case REG_TYPE_NOSPPCX:
+                       if (reg == 13 || reg == 15)
+                               return;
+                       break;
+
+               case REG_TYPE_NOPCWB:
+                       if (!is_writeback(insn))
+                               break;
+                       if (reg == 15) {
+                               entry->regs &= ~(COVERAGE_PCWB << i);
+                               return;
+                       }
+                       break;
+
+               case REG_TYPE_NOPC:
+               case REG_TYPE_NOPCX:
+                       if (reg == 15)
+                               return;
+                       break;
+               }
+
+       }
+}
+
+static void coverage_add(kprobe_opcode_t insn)
+{
+       struct coverage_entry *entry = coverage.base;
+       struct coverage_entry *end = coverage.base + coverage.num_entries;
+       bool matched = false;
+       unsigned nesting = 0;
+
+       for (; entry < end; ++entry) {
+               const struct decode_header *h = entry->header;
+               enum decode_type type = h->type_regs.bits & DECODE_TYPE_MASK;
+
+               if (entry->nesting > nesting)
+                       continue; /* Skip sub-table we didn't match */
+
+               if (entry->nesting < nesting)
+                       break; /* End of sub-table we were scanning */
+
+               if (!matched) {
+                       if ((insn & h->mask.bits) != h->value.bits)
+                               continue;
+                       entry->matched = true;
+               }
+
+               switch (type) {
+
+               case DECODE_TYPE_TABLE:
+                       ++nesting;
+                       break;
+
+               case DECODE_TYPE_CUSTOM:
+               case DECODE_TYPE_SIMULATE:
+               case DECODE_TYPE_EMULATE:
+                       coverage_add_registers(entry, insn);
+                       return;
+
+               case DECODE_TYPE_OR:
+                       matched = true;
+                       break;
+
+               case DECODE_TYPE_REJECT:
+               default:
+                       return;
+               }
+
+       }
+}
+
+static void coverage_end(void)
+{
+       struct coverage_entry *entry = coverage.base;
+       struct coverage_entry *end = coverage.base + coverage.num_entries;
+
+       for (; entry < end; ++entry) {
+               u32 mask = entry->header->mask.bits;
+               u32 value = entry->header->value.bits;
+
+               if (entry->regs) {
+                       pr_err("FAIL: Register test coverage missing for %08x %08x (%05x)\n",
+                               mask, value, entry->regs);
+                       coverage_fail = true;
+               }
+               if (!entry->matched) {
+                       pr_err("FAIL: Test coverage entry missing for %08x %08x\n",
+                               mask, value);
+                       coverage_fail = true;
+               }
+       }
+
+       kfree(coverage.base);
+}
+
+
 /*
  * Framework for instruction set test cases
  */
@@ -1039,6 +1284,8 @@ static uintptr_t __used kprobes_test_case_start(const char *title, void *stack)
                }
        }
 
+       coverage_add(current_instruction);
+
        if (end_arg->flags & ARG_FLAG_UNSUPPORTED) {
                if (register_test_probe(&test_case_probe) < 0)
                        goto pass;
@@ -1213,8 +1460,13 @@ static int run_test_cases(void (*tests)(void), const union decode_item *table)
                return ret;
 
        pr_info("    Run test cases\n");
+       ret = coverage_start(table);
+       if (ret)
+               return ret;
+
        tests();
 
+       coverage_end();
        return 0;
 }
 
@@ -1274,6 +1526,15 @@ static int __init run_all_tests(void)
                goto out;
        }
 
+#if __LINUX_ARM_ARCH__ >= 7
+       /* We are able to run all test cases so coverage should be complete */
+       if (coverage_fail) {
+               pr_err("FAIL: Test coverage checks failed\n");
+               ret = -EINVAL;
+               goto out;
+       }
+#endif
+
 out:
        if (ret == 0)
                pr_info("Finished kprobe tests OK\n");