Fuzzing Patches for 2021-09-01

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Merge remote-tracking branch 'remotes/a1xndr/tags/fuzz-pull-2021-09-01' into staging

Fuzzing Patches for 2021-09-01

# gpg: Signature made Wed 01 Sep 2021 12:42:00 BST
# gpg:                using RSA key FAD4E2BF871375D6340517C44E661DDE583A964E
# gpg: Good signature from "Alexander Bulekov <alxndr@bu.edu>" [unknown]
# gpg: WARNING: This key is not certified with a trusted signature!
# gpg:          There is no indication that the signature belongs to the owner.
# Primary key fingerprint: FAD4 E2BF 8713 75D6 3405  17C4 4E66 1DDE 583A 964E

* remotes/a1xndr/tags/fuzz-pull-2021-09-01:
  MAINTAINERS: add fuzzing reviewer
  MAINTAINERS: Add myself as a reviewer for Device Fuzzing
  fuzz: unblock SIGALRM so the timeout works
  fuzz: use ITIMER_REAL for timeouts
  fuzz: add an instrumentation filter
  fuzz: make object-name matching case-insensitive
  fuzz: adjust timeout to allow for longer inputs
  fuzz: fix sparse memory access in the DMA callback

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

MAINTAINERS

@@ -2760,6 +2760,8 @@ R: Paolo Bonzini <pbonzini@redhat.com>
 R: Bandan Das <bsd@redhat.com>
 R: Stefan Hajnoczi <stefanha@redhat.com>
 R: Thomas Huth <thuth@redhat.com>
+R: Darren Kenny <darren.kenny@oracle.com> 
+R: Qiuhao Li <Qiuhao.Li@outlook.com>
 S: Maintained
 F: tests/qtest/fuzz/
 F: tests/qtest/fuzz-*test.c

configure

@@ -4198,13 +4198,21 @@ fi
 
 ##########################################
 # checks for fuzzer
-if test "$fuzzing" = "yes" && test -z "${LIB_FUZZING_ENGINE+xxx}"; then
+if test "$fuzzing" = "yes" ; then
   write_c_fuzzer_skeleton
-  if compile_prog "$CPU_CFLAGS -Werror -fsanitize=fuzzer" ""; then
+  if test -z "${LIB_FUZZING_ENGINE+xxx}"; then
-    have_fuzzer=yes
+    if compile_prog "$CPU_CFLAGS -Werror -fsanitize=fuzzer" ""; then
-  else
+      have_fuzzer=yes
-    error_exit "Your compiler doesn't support -fsanitize=fuzzer"
+    else
-    exit 1
+      error_exit "Your compiler doesn't support -fsanitize=fuzzer"
+      exit 1
+    fi
+  fi
+
+  have_clang_coverage_filter=no
+  echo > $TMPTXT
+  if compile_prog "$CPU_CFLAGS -Werror -fsanitize=fuzzer -fsanitize-coverage-allowlist=$TMPTXT" ""; then
+    have_clang_coverage_filter=yes
   fi
 fi
 
@@ -4884,6 +4892,14 @@ if test "$fuzzing" = "yes" ; then
   else
     FUZZ_EXE_LDFLAGS="$LIB_FUZZING_ENGINE"
   fi
+
+  # Specify a filter to only instrument code that is directly related to
+  # virtual-devices.
+  if test "$have_clang_coverage_filter" = "yes" ; then
+    cp "$source_path/scripts/oss-fuzz/instrumentation-filter-template" \
+       instrumentation-filter
+    QEMU_CFLAGS="$QEMU_CFLAGS -fsanitize-coverage-allowlist=instrumentation-filter"
+  fi
 fi
 
 if test "$plugins" = "yes" ; then

scripts/oss-fuzz/instrumentation-filter-template

@@ -0,0 +1,15 @@
+# Code that we actually want the fuzzer to target
+# See: https://clang.llvm.org/docs/SanitizerCoverage.html#disabling-instrumentation-without-source-modification
+#
+src:*/hw/*
+src:*/include/hw/*
+src:*/slirp/*
+src:*/net/*
+
+# We don't care about coverage over fuzzer-specific code, however we should
+# instrument the fuzzer entry-point so libFuzzer always sees at least some
+# coverage - otherwise it will exit after the first input
+src:*/tests/qtest/fuzz/fuzz.c
+
+# Enable instrumentation for all functions in those files
+fun:*

tests/qtest/fuzz/generic_fuzz.c

@@ -240,10 +240,17 @@ void fuzz_dma_read_cb(size_t addr, size_t len, MemoryRegion *mr)
                                       addr, &addr1, &l, true,
                                       MEMTXATTRS_UNSPECIFIED);
 
-        if (!(memory_region_is_ram(mr1) ||
+        /*
-              memory_region_is_romd(mr1)) && mr1 != sparse_mem_mr) {
+         *  If mr1 isn't RAM, address_space_translate doesn't update l. Use
+         *  memory_access_size to identify the number of bytes that it is safe
+         *  to write without accidentally writing to another MemoryRegion.
+         */
+        if (!memory_region_is_ram(mr1)) {
             l = memory_access_size(mr1, l, addr1);
-        } else {
+        }
+        if (memory_region_is_ram(mr1) ||
+            memory_region_is_romd(mr1) ||
+            mr1 == sparse_mem_mr) {
             /* ROM/RAM case */
             if (qtest_log_enabled) {
                 /*
@@ -661,31 +668,41 @@ static void generic_fuzz(QTestState *s, const unsigned char *Data, size_t Size)
     uint8_t op;
 
     if (fork() == 0) {
+        struct sigaction sact;
+        struct itimerval timer;
+        sigset_t set;
         /*
          * Sometimes the fuzzer will find inputs that take quite a long time to
          * process. Often times, these inputs do not result in new coverage.
          * Even if these inputs might be interesting, they can slow down the
-         * fuzzer, overall. Set a timeout to avoid hurting performance, too much
+         * fuzzer, overall. Set a timeout for each command to avoid hurting
+         * performance, too much
          */
         if (timeout) {
-            struct sigaction sact;
-            struct itimerval timer;
 
             sigemptyset(&sact.sa_mask);
             sact.sa_flags   = SA_NODEFER;
             sact.sa_handler = handle_timeout;
             sigaction(SIGALRM, &sact, NULL);
 
+            sigemptyset(&set);
+            sigaddset(&set, SIGALRM);
+            pthread_sigmask(SIG_UNBLOCK, &set, NULL);
+
             memset(&timer, 0, sizeof(timer));
             timer.it_value.tv_sec = timeout / USEC_IN_SEC;
             timer.it_value.tv_usec = timeout % USEC_IN_SEC;
-            setitimer(ITIMER_VIRTUAL, &timer, NULL);
         }
 
         op_clear_dma_patterns(s, NULL, 0);
         pci_disabled = false;
 
         while (cmd && Size) {
+            /* Reset the timeout, each time we run a new command */
+            if (timeout) {
+                setitimer(ITIMER_REAL, &timer, NULL);
+            }
+
             /* Get the length until the next command or end of input */
             nextcmd = memmem(cmd, Size, SEPARATOR, strlen(SEPARATOR));
             cmd_len = nextcmd ? nextcmd - cmd : Size;
@@ -746,8 +763,13 @@ static int locate_fuzz_memory_regions(Object *child, void *opaque)
 
 static int locate_fuzz_objects(Object *child, void *opaque)
 {
+    GString *type_name;
+    GString *path_name;
     char *pattern = opaque;
-    if (g_pattern_match_simple(pattern, object_get_typename(child))) {
+
+    type_name = g_string_new(object_get_typename(child));
+    g_string_ascii_down(type_name);
+    if (g_pattern_match_simple(pattern, type_name->str)) {
         /* Find and save ptrs to any child MemoryRegions */
         object_child_foreach_recursive(child, locate_fuzz_memory_regions, NULL);
 
@@ -764,8 +786,9 @@ static int locate_fuzz_objects(Object *child, void *opaque)
             g_ptr_array_add(fuzzable_pci_devices, PCI_DEVICE(child));
         }
     } else if (object_dynamic_cast(OBJECT(child), TYPE_MEMORY_REGION)) {
-        if (g_pattern_match_simple(pattern,
+        path_name = g_string_new(object_get_canonical_path_component(child));
-            object_get_canonical_path_component(child))) {
+        g_string_ascii_down(path_name);
+        if (g_pattern_match_simple(pattern, path_name->str)) {
             MemoryRegion *mr;
             mr = MEMORY_REGION(child);
             if ((memory_region_is_ram(mr) ||
@@ -774,7 +797,9 @@ static int locate_fuzz_objects(Object *child, void *opaque)
                 g_hash_table_insert(fuzzable_memoryregions, mr, (gpointer)true);
             }
         }
+        g_string_free(path_name, true);
     }
+    g_string_free(type_name, true);
     return 0;
 }
 
@@ -802,6 +827,7 @@ static void generic_pre_fuzz(QTestState *s)
     MemoryRegion *mr;
     QPCIBus *pcibus;
     char **result;
+    GString *name_pattern;
 
     if (!getenv("QEMU_FUZZ_OBJECTS")) {
         usage();
@@ -831,10 +857,17 @@ static void generic_pre_fuzz(QTestState *s)
 
     result = g_strsplit(getenv("QEMU_FUZZ_OBJECTS"), " ", -1);
     for (int i = 0; result[i] != NULL; i++) {
+        name_pattern = g_string_new(result[i]);
+        /*
+         * Make the pattern lowercase. We do the same for all the MemoryRegion
+         * and Type names so the configs are case-insensitive.
+         */
+        g_string_ascii_down(name_pattern);
         printf("Matching objects by name %s\n", result[i]);
         object_child_foreach_recursive(qdev_get_machine(),
                                     locate_fuzz_objects,
-                                    result[i]);
+                                    name_pattern->str);
+        g_string_free(name_pattern, true);
     }
     g_strfreev(result);
     printf("This process will try to fuzz the following MemoryRegions:\n");