1 files changed, 186 insertions, 0 deletions
diff --git a/linker/linker_note_gnu_property.cpp b/linker/linker_note_gnu_property.cpp
new file mode 100644
index 000000000..be1aebc88
--- /dev/null
+++ b/linker/linker_note_gnu_property.cpp
@@ -0,0 +1,186 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include "linker_note_gnu_property.h"
+
+#include <elf.h>
+#include <link.h>
+
+#include "linker.h"
+#include "linker_debug.h"
+#include "linker_globals.h"
+#include "linker_soinfo.h"
+
+GnuPropertySection::GnuPropertySection(const soinfo* si)
+    : GnuPropertySection(si->phdr, si->phnum, si->load_bias, si->get_realpath()) {}
+
+GnuPropertySection::GnuPropertySection(const ElfW(Phdr)* phdr, size_t phdr_count,
+                                       const ElfW(Addr) load_bias, const char* name) {
+  // Try to find PT_GNU_PROPERTY segment.
+  auto note_gnu_property = FindSegment(phdr, phdr_count, load_bias, name);
+  // Perform some validity checks.
+  if (note_gnu_property && SanityCheck(note_gnu_property, name)) {
+    // Parse section.
+    Parse(note_gnu_property, name);
+  }
+}
+
+const ElfW(NhdrGNUProperty)* GnuPropertySection::FindSegment(const ElfW(Phdr)* phdr,
+                                                             size_t phdr_count,
+                                                             const ElfW(Addr) load_bias,
+                                                             const char* name) const {
+  // According to Linux gABI extension this segment should contain
+  // .note.gnu.property section only.
+  if (phdr != nullptr) {
+    for (size_t i = 0; i < phdr_count; ++i) {
+      if (phdr[i].p_type != PT_GNU_PROPERTY) {
+        continue;
+      }
+
+      TRACE("\"%s\" PT_GNU_PROPERTY: found at segment index %zu", name, i);
+
+      // Check segment size.
+      if (phdr[i].p_memsz < sizeof(ElfW(NhdrGNUProperty))) {
+        DL_ERR_AND_LOG(
+            "\"%s\" PT_GNU_PROPERTY segment is too small. Segment "
+            "size is %zu, minimum is %zu.",
+            name, static_cast<size_t>(phdr[i].p_memsz), sizeof(ElfW(NhdrGNUProperty)));
+        return nullptr;
+      }
+
+      // PT_GNU_PROPERTY contains .note.gnu.property which has SHF_ALLOC
+      // attribute, therefore it is loaded.
+      auto note_nhdr = reinterpret_cast<ElfW(NhdrGNUProperty)*>(load_bias + phdr[i].p_vaddr);
+
+      // Check that the n_descsz <= p_memsz
+      if ((phdr[i].p_memsz - sizeof(ElfW(NhdrGNUProperty))) < note_nhdr->nhdr.n_descsz) {
+        DL_ERR_AND_LOG(
+            "\"%s\" PT_GNU_PROPERTY segment p_memsz (%zu) is too small for note n_descsz (%zu).",
+            name, static_cast<size_t>(phdr[i].p_memsz),
+            static_cast<size_t>(note_nhdr->nhdr.n_descsz));
+        return nullptr;
+      }
+
+      return note_nhdr;
+    }
+  }
+
+  TRACE("\"%s\" PT_GNU_PROPERTY: not found", name);
+  return nullptr;
+}
+
+bool GnuPropertySection::SanityCheck(const ElfW(NhdrGNUProperty)* note_nhdr,
+                                     const char* name) const {
+  // Check .note section type
+  if (note_nhdr->nhdr.n_type != NT_GNU_PROPERTY_TYPE_0) {
+    DL_ERR_AND_LOG("\"%s\" .note.gnu.property: unexpected note type. Expected %u, got %u.", name,
+                   NT_GNU_PROPERTY_TYPE_0, note_nhdr->nhdr.n_type);
+    return false;
+  }
+
+  if (note_nhdr->nhdr.n_namesz != 4) {
+    DL_ERR_AND_LOG("\"%s\" .note.gnu.property: unexpected name size. Expected 4, got %u.", name,
+                   note_nhdr->nhdr.n_namesz);
+    return false;
+  }
+
+  if (strncmp(note_nhdr->n_name, "GNU", 4) != 0) {
+    DL_ERR_AND_LOG("\"%s\" .note.gnu.property: unexpected name. Expected 'GNU', got '%s'.", name,
+                   note_nhdr->n_name);
+    return false;
+  }
+
+  return true;
+}
+
+bool GnuPropertySection::Parse(const ElfW(NhdrGNUProperty)* note_nhdr, const char* name) {
+  // The total length of the program property array is in _bytes_.
+  ElfW(Word) offset = 0;
+  while (offset < note_nhdr->nhdr.n_descsz) {
+    DEBUG("\"%s\" .note.gnu.property: processing at offset 0x%x", name, offset);
+
+    // At least the "header" part must fit.
+    // The ABI doesn't say that pr_datasz can't be 0.
+    if ((note_nhdr->nhdr.n_descsz - offset) < sizeof(ElfW(Prop))) {
+      DL_ERR_AND_LOG(
+          "\"%s\" .note.gnu.property: no more space left for a "
+          "Program Property Note header.",
+          name);
+      return false;
+    }
+
+    // Loop on program property array.
+    const ElfW(Prop)* property = reinterpret_cast<const ElfW(Prop)*>(&note_nhdr->n_desc[offset]);
+    const ElfW(Word) property_size =
+        align_up(sizeof(ElfW(Prop)) + property->pr_datasz, sizeof(ElfW(Addr)));
+    if ((note_nhdr->nhdr.n_descsz - offset) < property_size) {
+      DL_ERR_AND_LOG(
+          "\"%s\" .note.gnu.property: property descriptor size is "
+          "invalid. Expected at least %u bytes, got %u.",
+          name, property_size, note_nhdr->nhdr.n_descsz - offset);
+      return false;
+    }
+
+    // Cache found properties.
+    switch (property->pr_type) {
+#if defined(__aarch64__)
+      case GNU_PROPERTY_AARCH64_FEATURE_1_AND: {
+        if (property->pr_datasz != 4) {
+          DL_ERR_AND_LOG(
+              "\"%s\" .note.gnu.property: property descriptor size is "
+              "invalid. Expected %u bytes for GNU_PROPERTY_AARCH64_FEATURE_1_AND, got %u.",
+              name, 4, property->pr_datasz);
+          return false;
+        }
+
+        const ElfW(Word) flags = *reinterpret_cast<const ElfW(Word)*>(&property->pr_data[0]);
+        properties_.bti_compatible = (flags & GNU_PROPERTY_AARCH64_FEATURE_1_BTI) != 0;
+        if (properties_.bti_compatible) {
+          INFO("[ BTI compatible: \"%s\" ]", name);
+        }
+        break;
+      }
+#endif
+      default:
+        DEBUG("\"%s\" .note.gnu.property: found property pr_type %u pr_datasz 0x%x", name,
+              property->pr_type, property->pr_datasz);
+        break;
+    }
+
+    // Move offset, this should be safe to add because of previous checks.
+    offset += property_size;
+  }
+
+  return true;
+}
+
+#if defined(__aarch64__)
+bool GnuPropertySection::IsBTICompatible() const {
+  return (g_platform_properties.bti_supported && properties_.bti_compatible);
+}
+#endif