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>

1 files changed, 261 insertions, 0 deletions

diff --git a/arch/arm/kernel/kprobes-test.c b/arch/arm/kernel/kprobes-test.c
index 6c0946c023f..fe169e934d4 100644
--- 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"
@@ -529,6 +530,250 @@ 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");