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Allow sharing the RELRO section via a file.

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Add flags and a file descriptor to android_dlopen_ext() to allow writing
the RELRO section of the loaded library to a file after relocation
processing, and to allow mapping identical pages from the file over the
top of relocated memory in another process. Explicitly comparing the
pages is required in case a page contains a reference to a symbol
defined in another library loaded at a random base address.

Bug: 13005501
Change-Id: Ibb5b2d384edfaa5acf3e97a5f8b6115c10497a1e
This commit is contained in:
Torne (Richard Coles)
2014-02-27 13:18:00 +00:00
parent 12bbb91645
commit 183ad9df53
5 changed files with 226 additions and 6 deletions
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56
tests/dlext_test.cpp
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@@ -17,8 +17,14 @@
#include <gtest/gtest.h>
#include <dlfcn.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <android/dlext.h>
#include <sys/mman.h>
#include <sys/wait.h>
#define ASSERT_DL_NOTNULL(ptr) \
@@ -27,10 +33,14 @@
#define ASSERT_DL_ZERO(i) \
ASSERT_EQ(0, i) << "dlerror: " << dlerror()
#define ASSERT_NOERROR(i) \
ASSERT_NE(-1, i) << "errno: " << strerror(errno)
typedef int (*fn)(void);
#define LIBNAME "libdlext_test.so"
#define LIBSIZE 1024*1024 // how much address space to reserve for it
#define RELRO_FILE "/data/local/tmp/libdlext_test.relro"
class DlExtTest : public ::testing::Test {
@@ -134,3 +144,49 @@ TEST_F(DlExtTest, ReservedHintTooSmall) {
reinterpret_cast<char*>(start) + PAGE_SIZE));
EXPECT_EQ(4, f());
}
TEST_F(DlExtTest, RelroShareChildWrites) {
void* start = mmap(NULL, LIBSIZE, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS,
-1, 0);
ASSERT_TRUE(start != MAP_FAILED);
android_dlextinfo extinfo;
extinfo.reserved_addr = start;
extinfo.reserved_size = LIBSIZE;
int relro_fd;
relro_fd = open(RELRO_FILE, O_CREAT | O_RDWR | O_TRUNC, 0644);
extinfo.flags = ANDROID_DLEXT_RESERVED_ADDRESS | ANDROID_DLEXT_WRITE_RELRO;
ASSERT_NOERROR(relro_fd);
extinfo.relro_fd = relro_fd;
pid_t pid = fork();
if (pid == 0) {
// child process
void* handle = android_dlopen_ext(LIBNAME, RTLD_NOW, &extinfo);
if (handle == NULL) {
fprintf(stderr, "in child: %s\n", dlerror());
exit(1);
}
exit(0);
}
// continuing in parent
ASSERT_NOERROR(close(relro_fd));
ASSERT_NOERROR(pid);
int status;
ASSERT_EQ(pid, waitpid(pid, &status, 0));
ASSERT_TRUE(WIFEXITED(status));
ASSERT_EQ(0, WEXITSTATUS(status));
relro_fd = open(RELRO_FILE, O_RDONLY);
ASSERT_NOERROR(relro_fd);
extinfo.flags = ANDROID_DLEXT_RESERVED_ADDRESS | ANDROID_DLEXT_USE_RELRO;
extinfo.relro_fd = relro_fd;
handle_ = android_dlopen_ext(LIBNAME, RTLD_NOW, &extinfo);
ASSERT_NOERROR(close(relro_fd));
ASSERT_DL_NOTNULL(handle_);
fn f = reinterpret_cast<fn>(dlsym(handle_, "getRandomNumber"));
ASSERT_DL_NOTNULL(f);
EXPECT_EQ(4, f());
}