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Add support for symbolicating APK/ZIP-embedded libraries on Android
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By default, modern Android build tools will store native libraries
uncompressed, and the loader will map them directly from the APK
(instead of the package manager extracting them on installation).

This commit adds support for symbolicating these embedded libraries.

To avoid parsing ZIP structures, the offset of the library within the
archive is determined via /proc/self/maps.

ref: https://android.googlesource.com/platform/bionic/+/main/android-changes-for-ndk-developers.md#opening-shared-libraries-directly-from-an-apk
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sudoBash418 committed Sep 9, 2024
1 parent 386a42a commit 6319c02
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Showing 7 changed files with 149 additions and 38 deletions.
47 changes: 38 additions & 9 deletions src/symbolize/gimli.rs
Original file line number Diff line number Diff line change
Expand Up @@ -186,7 +186,7 @@ impl<'data> Context<'data> {
fn mmap(path: &Path) -> Option<Mmap> {
let file = File::open(path).ok()?;
let len = file.metadata().ok()?.len().try_into().ok()?;
unsafe { Mmap::map(&file, len) }
unsafe { Mmap::map(&file, len, 0) }
}

cfg_if::cfg_if! {
Expand Down Expand Up @@ -268,6 +268,21 @@ struct Cache {

struct Library {
name: OsString,
#[cfg(target_os = "android")]
/// On Android, the dynamic linker [can map libraries directly from a
/// ZIP archive][ndk-linker-changes] (typically an `.apk`).
///
/// The linker requires that these libraries are stored uncompressed
/// and page-aligned.
///
/// These "embedded" libraries have filepaths of the form
/// `/path/to/my.apk!/lib/mylib.so` (where `/path/to/my.apk` is the archive
/// and `lib/mylib.so` is the name of the library within the archive).
///
/// This mechanism is present on Android since API level 23.
///
/// [ndk-linker-changes]: https://android.googlesource.com/platform/bionic/+/main/android-changes-for-ndk-developers.md#opening-shared-libraries-directly-from-an-apk
zip_offset: Option<u64>,
#[cfg(target_os = "aix")]
/// On AIX, the library mmapped can be a member of a big-archive file.
/// For example, with a big-archive named libfoo.a containing libbar.so,
Expand All @@ -294,17 +309,31 @@ struct LibrarySegment {
len: usize,
}

#[cfg(target_os = "aix")]
fn create_mapping(lib: &Library) -> Option<Mapping> {
let name = &lib.name;
let member_name = &lib.member_name;
Mapping::new(name.as_ref(), member_name)
cfg_if::cfg_if! {
if #[cfg(target_os = "aix")] {
Mapping::new(lib.name.as_ref(), &lib.member_name)
} else if #[cfg(target_os = "android")] {
Mapping::new_android(lib.name.as_ref(), lib.zip_offset)
} else {
Mapping::new(lib.name.as_ref())
}
}
}

#[cfg(not(target_os = "aix"))]
fn create_mapping(lib: &Library) -> Option<Mapping> {
let name = &lib.name;
Mapping::new(name.as_ref())
/// Try to extract the archive path from an "embedded" library path
/// (e.g. `/path/to/my.apk` from `/path/to/my.apk!/mylib.so`).
///
/// Returns `None` if the path does not contain a `!/` separator.
#[cfg(target_os = "android")]
fn extract_zip_path_android(path: &mystd::ffi::OsStr) -> Option<&mystd::ffi::OsStr> {
use mystd::os::unix::ffi::OsStrExt;

path.as_bytes()
.windows(2)
.enumerate()
.find(|(_, chunk)| chunk == b"!/")
.map(|(index, _)| mystd::ffi::OsStr::from_bytes(path.as_bytes().split_at(index).0))
}

// unsafe because this is required to be externally synchronized
Expand Down
41 changes: 41 additions & 0 deletions src/symbolize/gimli/elf.rs
Original file line number Diff line number Diff line change
Expand Up @@ -45,6 +45,47 @@ impl Mapping {
})
}

/// On Android, shared objects can be loaded directly from a ZIP archive
/// (see: [`super::Library::zip_offset`]).
///
/// If `zip_offset` is not None, we interpret the `path` as an
/// "embedded" library path, and the value of `zip_offset` tells us where
/// in the ZIP archive the library data starts.
///
/// We expect `zip_offset` to be page-aligned because the dynamic linker
/// requires this. Otherwise, loading the embedded library will fail.
///
/// If we fail to load an embedded library for any reason, we fallback to
/// interpreting the path as a literal file on disk (same as calling [`Self::new`]).
#[cfg(target_os = "android")]
pub fn new_android(path: &Path, zip_offset: Option<u64>) -> Option<Mapping> {
fn map_embedded_library(path: &Path, zip_offset: u64) -> Option<Mapping> {
// get path of ZIP archive (delimited by `!/`)
let zip_path = Path::new(super::extract_zip_path_android(path.as_os_str())?);

let file = fs::File::open(zip_path).ok()?;
let len = file.metadata().ok()?.len();

// NOTE: we map the remainder of the entire archive instead of just the library so we don't have to determine its length
// NOTE: mmap will fail if `zip_offset` is not page-aligned
let map = unsafe {
super::mmap::Mmap::map(&file, usize::try_from(len - zip_offset).ok()?, zip_offset)
}?;

Mapping::mk(map, |map, stash| {
Context::new(stash, Object::parse(&map)?, None, None)
})
}

// if ZIP offset is given, try mapping as a ZIP-embedded library
// otherwise, fallback to mapping as a literal filepath
if let Some(zip_offset) = zip_offset {
map_embedded_library(path, zip_offset).or_else(|| Self::new(path))
} else {
Self::new(path)
}
}

/// Load debuginfo from an external debug file.
fn new_debug(original_path: &Path, path: PathBuf, crc: Option<u32>) -> Option<Mapping> {
let map = super::mmap(&path)?;
Expand Down
68 changes: 47 additions & 21 deletions src/symbolize/gimli/libs_dl_iterate_phdr.rs
Original file line number Diff line number Diff line change
Expand Up @@ -6,51 +6,62 @@ use super::mystd::borrow::ToOwned;
use super::mystd::env;
use super::mystd::ffi::{CStr, OsStr};
use super::mystd::os::unix::prelude::*;
use super::{Library, LibrarySegment, OsString, Vec};
use super::{parse_running_mmaps, Library, LibrarySegment, OsString, Vec};
use core::slice;

struct CallbackData {
libs: Vec<Library>,
maps: Option<Vec<parse_running_mmaps::MapsEntry>>,
}
pub(super) fn native_libraries() -> Vec<Library> {
let mut ret = Vec::new();
let mut cb_data = CallbackData {
libs: Vec::new(),
#[cfg(not(target_os = "hurd"))]
maps: parse_running_mmaps::parse_maps().ok(),
#[cfg(target_os = "hurd")]
maps: None,
};
unsafe {
libc::dl_iterate_phdr(Some(callback), core::ptr::addr_of_mut!(ret).cast());
libc::dl_iterate_phdr(Some(callback), core::ptr::addr_of_mut!(cb_data).cast());
}
ret
cb_data.libs
}

fn infer_current_exe(base_addr: usize) -> OsString {
cfg_if::cfg_if! {
if #[cfg(not(target_os = "hurd"))] {
if let Ok(entries) = super::parse_running_mmaps::parse_maps() {
let opt_path = entries
.iter()
.find(|e| e.ip_matches(base_addr) && e.pathname().len() > 0)
.map(|e| e.pathname())
.cloned();
if let Some(path) = opt_path {
return path;
}
}
fn infer_current_exe(
maps: &Option<Vec<parse_running_mmaps::MapsEntry>>,
base_addr: usize,
) -> OsString {
#[cfg(not(target_os = "hurd"))]
if let Some(entries) = maps {
let opt_path = entries
.iter()
.find(|e| e.ip_matches(base_addr) && e.pathname().len() > 0)
.map(|e| e.pathname())
.cloned();
if let Some(path) = opt_path {
return path;
}
}

env::current_exe().map(|e| e.into()).unwrap_or_default()
}

/// # Safety
/// `info` must be a valid pointer.
/// `vec` must be a valid pointer to `Vec<Library>`
/// `data` must be a valid pointer to `CallbackData`.
#[forbid(unsafe_op_in_unsafe_fn)]
unsafe extern "C" fn callback(
info: *mut libc::dl_phdr_info,
_size: libc::size_t,
vec: *mut libc::c_void,
data: *mut libc::c_void,
) -> libc::c_int {
// SAFETY: We are guaranteed these fields:
let dlpi_addr = unsafe { (*info).dlpi_addr };
let dlpi_name = unsafe { (*info).dlpi_name };
let dlpi_phdr = unsafe { (*info).dlpi_phdr };
let dlpi_phnum = unsafe { (*info).dlpi_phnum };
// SAFETY: We assured this.
let libs = unsafe { &mut *vec.cast::<Vec<Library>>() };
let CallbackData { libs, maps } = unsafe { &mut *data.cast::<CallbackData>() };
// most implementations give us the main program first
let is_main = libs.is_empty();
// we may be statically linked, which means we are main and mostly one big blob of code
Expand All @@ -63,7 +74,7 @@ unsafe extern "C" fn callback(
// don't try to look up our name from /proc/self/maps, it'll get silly
env::current_exe().unwrap_or_default().into_os_string()
} else if is_main && no_given_name {
infer_current_exe(dlpi_addr as usize)
infer_current_exe(&maps, dlpi_addr as usize)
} else {
// this fallback works even if we are main, because some platforms give the name anyways
if dlpi_name.is_null() {
Expand All @@ -73,6 +84,19 @@ unsafe extern "C" fn callback(
OsStr::from_bytes(unsafe { CStr::from_ptr(dlpi_name) }.to_bytes()).to_owned()
}
};
#[cfg(target_os = "android")]
let zip_offset: Option<u64> = {
// only check for ZIP-embedded file if we have data from /proc/self/maps
maps.as_ref().and_then(|maps| {
// check if file is embedded within a ZIP archive by searching for `!/`
super::extract_zip_path_android(&name).and_then(|_| {
// find MapsEntry matching library's base address and get its file offset
maps.iter()
.find(|m| m.ip_matches(dlpi_addr as usize))
.map(|m| m.offset())
})
})
};
let headers = if dlpi_phdr.is_null() || dlpi_phnum == 0 {
&[]
} else {
Expand All @@ -81,6 +105,8 @@ unsafe extern "C" fn callback(
};
libs.push(Library {
name,
#[cfg(target_os = "android")]
zip_offset,
segments: headers
.iter()
.map(|header| LibrarySegment {
Expand Down
6 changes: 4 additions & 2 deletions src/symbolize/gimli/mmap_fake.rs
Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
use super::{mystd::io::Read, File};
use super::mystd::io::{Read, Seek, SeekFrom};
use super::File;
use alloc::vec::Vec;
use core::ops::Deref;

Expand All @@ -7,10 +8,11 @@ pub struct Mmap {
}

impl Mmap {
pub unsafe fn map(mut file: &File, len: usize) -> Option<Mmap> {
pub unsafe fn map(mut file: &File, len: usize, offset: u64) -> Option<Mmap> {
let mut mmap = Mmap {
vec: Vec::with_capacity(len),
};
file.seek(SeekFrom::Start(offset));
file.read_to_end(&mut mmap.vec).ok()?;
Some(mmap)
}
Expand Down
4 changes: 2 additions & 2 deletions src/symbolize/gimli/mmap_unix.rs
Original file line number Diff line number Diff line change
Expand Up @@ -15,14 +15,14 @@ pub struct Mmap {
}

impl Mmap {
pub unsafe fn map(file: &File, len: usize) -> Option<Mmap> {
pub unsafe fn map(file: &File, len: usize, offset: u64) -> Option<Mmap> {
let ptr = mmap64(
ptr::null_mut(),
len,
libc::PROT_READ,
libc::MAP_PRIVATE,
file.as_raw_fd(),
0,
offset.try_into().ok()?,
);
if ptr == libc::MAP_FAILED {
return None;
Expand Down
10 changes: 8 additions & 2 deletions src/symbolize/gimli/mmap_windows.rs
Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,7 @@ pub struct Mmap {
}

impl Mmap {
pub unsafe fn map(file: &File, len: usize) -> Option<Mmap> {
pub unsafe fn map(file: &File, len: usize, offset: u64) -> Option<Mmap> {
let file = file.try_clone().ok()?;
let mapping = CreateFileMappingA(
file.as_raw_handle(),
Expand All @@ -29,7 +29,13 @@ impl Mmap {
if mapping.is_null() {
return None;
}
let ptr = MapViewOfFile(mapping, FILE_MAP_READ, 0, 0, len);
let ptr = MapViewOfFile(
mapping,
FILE_MAP_READ,
(offset >> 32) as u32,
offset as u32,
len,
);
CloseHandle(mapping);
if ptr.Value.is_null() {
return None;
Expand Down
11 changes: 9 additions & 2 deletions src/symbolize/gimli/parse_running_mmaps_unix.rs
Original file line number Diff line number Diff line change
Expand Up @@ -20,7 +20,7 @@ pub(super) struct MapsEntry {
/// p = private (copy on write)
perms: [char; 4],
/// Offset into the file (or "whatever").
offset: usize,
offset: u64,
/// device (major, minor)
dev: (usize, usize),
/// inode on the device. 0 indicates that no inode is associated with the memory region (e.g. uninitalized data aka BSS).
Expand Down Expand Up @@ -76,6 +76,11 @@ impl MapsEntry {
pub(super) fn ip_matches(&self, ip: usize) -> bool {
self.address.0 <= ip && ip < self.address.1
}

#[cfg(target_os = "android")]
pub(super) fn offset(&self) -> u64 {
self.offset
}
}

impl FromStr for MapsEntry {
Expand Down Expand Up @@ -118,6 +123,8 @@ impl FromStr for MapsEntry {
let pathname_str = s.trim_start();

let hex = |s| usize::from_str_radix(s, 16).map_err(|_| "Couldn't parse hex number");
let hex64 = |s| u64::from_str_radix(s, 16).map_err(|_| "Couldn't parse hex number");

let address = if let Some((start, limit)) = range_str.split_once('-') {
(hex(start)?, hex(limit)?)
} else {
Expand All @@ -132,7 +139,7 @@ impl FromStr for MapsEntry {
}
perms
};
let offset = hex(offset_str)?;
let offset = hex64(offset_str)?;
let dev = if let Some((major, minor)) = dev_str.split_once(':') {
(hex(major)?, hex(minor)?)
} else {
Expand Down

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