The clang-r370808 upgrade contains a change to LLD allow PT_LOAD
segments to reside at non-multiples of the page size in the resulting
object file. https://reviews.llvm.org/rL369344
While this helps reduce the alignment waste and resulting image size, it
has interesting implications for execute only memory (XOM): The runtime
loader will now load code or data from other segments into pages with
different protections than intended.
This would partially defeat execute only (XOM) text sections as the
segment could now overlap with previous and following sections. This
might allow for code or data from the preceding and following sections
(like .eh_frame, and .data.rel.ro) to be executable, and either ends of
.text to be readable.
When the runtime loader (linker[64]) `mmap`s segments from *.so files,
the file offset parameter (see `man 2 mmap`) MUST be a multiple of the
page size. Since the updated LLD can now pack segments in a file (which
helps minimize resulting object file size) (previously, the segment
offsets were page aligned), this has interesting implications.
To appreciate the current bug, consider the following output from
`readelf` before this patch is applied, but after the toolchain upgrade:
```
$ readelf -lSW $OUT/symbols/apex/com.android.runtime/lib64/bionic/libc.so
...
[Nr] Name Type Address Off Size ES Flg Lk Inf Al
...
[13] .eh_frame PROGBITS 000000000002e7c0 02e7c0 013374 00 A 0 0 8
[14] .text PROGBITS 0000000000042b40 041b40 09ecb4 00 AX 0 0 64
[15] .plt PROGBITS 00000000000e1800 0e0800 001f30 00 AX 0 0 16
[16] .data.rel.ro PROGBITS 00000000000e4740 0e2740 005208 00 WA 0 0 32
...
Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
PHDR 0x000040 0x0000000000000040 0x0000000000000040 0x000230 0x000230 R 0x8
LOAD 0x000000 0x0000000000000000 0x0000000000000000 0x041b34 0x041b34 R 0x1000
LOAD 0x041b40 0x0000000000042b40 0x0000000000042b40 0x0a0bf0 0x0a0bf0 E 0x1000
LOAD 0x0e2740 0x00000000000e4740 0x00000000000e4740 0x006720 0x006720 RW 0x1000
...
01 .note.android.ident .note.gnu.build-id .dynsym .gnu.version .gnu.version_d .gnu.version_r .gnu.hash .dynstr .rela.dyn .rela.plt .rodata .eh_frame_hdr .eh_frame
02 .text .plt
03 .data.rel.ro .fini_array .init_array .dynamic .got .got.plt
...
The above output tells us:
1. .text will wind up in the third (02) segment.
2. The third segment will be (LOAD)'ed as (E)xecutable.
3. Because the file (Offset) of the first segment (0x41b40) is NOT a
multiple of the page size, it cannot be passed as the `offset` to
`mmap`. As such it will be rounded down to the first multiple of the
page size, 0x41000.
4. The preceding section (.eh_frame) will be loaded in the preceding
segment (01). It occupies file (Off)set range [(0x2e7c0):0x41b34].
0x41b34 is not explicit in the output, instead you must use the
formula:
Off + Size == End
ie.
0x2e7c0 + 0x13374 == 0x41b34
(This happens to match (FileSiz) of the second segment, which makes
sense as .eh_frame is the final section in the second segment.)
5. mmap'ing file offset 0x41000 when loading the second segment will
include 0x4c0 bytes (0x42000 - 0x41b40) from .text, now mapped as
readable (oops). Suddenly code from .text is now readable (and thus
scannable for gadgets for ROP chains).
6. mmap'ing file offset 0x41000 when loading the third segment will
include 0xb34 bytes (0x41b34 - 0x41000) from .eh_frame, now mapped as
executable (oops). Suddenly data from .eh_frame is now executable
(and thus a potential gadget for ROP chains).
7. mmap'ing file offset 0xe2000 when loading the third segment will
include 0x8CO bytes (0xe3000 - 0xe2740) from .data.rel.ro, now mapped
as executable (oops). Suddenly data from .data.rel.ro is now
executable (and thus a potential gadget for ROP chains).
8. mmap'ing file offset 0xe2000 when loading the fourth segment will
include 0x730 bytes (0xe0800 + 0x1f30 - 0xe2000) from .plt, now
mapped as readable (oops). Suddenly data from .plt is now readable
(and thus scannable for gadgets for ROP chains).
All these oops' could be avoided if the linker placed .text+.plt at page
size aligned file offsets, which is what `-Wl,-z,separate-code` code
does. After this patch, we have:
```
$ readelf -lSW $OUT/symbols/apex/com.android.runtime/lib64/bionic/libc.so
...
Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align
PHDR 0x000040 0x0000000000000040 0x0000000000000040 0x000230 0x000230 R 0x8
LOAD 0x000000 0x0000000000000000 0x0000000000000000 0x041b34 0x041b34 R 0x1000
LOAD 0x042000 0x0000000000042000 0x0000000000042000 0x0a0be0 0x0a0be0 E 0x1000
LOAD 0x0e3000 0x00000000000e3000 0x00000000000e3000 0x006720 0x006720 RW 0x1000
```
In the future, we could go back to tightly packing segments in the
binary if the runtime loader was improved to detect the previously
stated problem, and `memset` over the problematic ranges of the freshly
`mmap`ed pages (implying additional startup cost for reduced binary
size). This might save ~6 KB from each native binary, which adds up to
~17 MB for an AOSP image.
Also, prefer
-Wl,--execute-only
rather than
-Wl,-execute-only
Bug: 139945549
Bug: 146144180
Test: readelf -lSW $OUT/symbols/apex/com.android.runtime/lib64/bionic/libc.so
Change-Id: I64527e034ca3c71565ea52ed06f81f75d5216627
Reported-by: Ryan Prichard <rprichard@google.com>
Suggested-by: Fangrui Song <maskray@google.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
When a boot classpath java library is directly or indirectly included in
APEXes, multiple variant of the library exist. When running the
hiddenapi tool, we need to eliminate the duplication, otherwise the tool
will complain.
Previously, we simply choose the platform variant of the java library
among the multiple variants. However, if the java library is marked not
available for the platform (i.e. "//apex_available:platform" is not in
the apex_available property), the platform variant does not exist and
thus it is not fed into the hiddenapi tool, which causes missing
references in the tool.
To solve the problem, the platform variant is selected only for the java
libs that are available for the platform. For those libs that are not
available for the platform, we choose one variant of it using a
heuristic; skip testing APEXes and choose com.android.art.release among
the com.android.art.* variants.
Bug: 128708192
Test: m
Change-Id: I33bf297eb3029696ae3504a011486210708fb2c2
The main purpose of apex_available is to prevent a module from being
installed to the system partition (or being statically linked to
something that is installed to the system partition). It's not the goal
to prevent host tools from using the modules.
However, since both host and device variants are not mutated for
platform when the module is not available to platform, the host tools
that depends on those modules couldn't be built. To solve the problem,
the platform variation is NOT skipped for the host variants.
Bug: 128708192
Test: m
Change-Id: I1d662cd6d165581f344138d872329a15bfc43d17
This change fixes a bug that LOCAL_PATH for modules included in an APEX
is set to the path of the APEX bundle, not to the path of the embedded
module. For example, LOCAL_PATH of libconscrypt included in
com.android.adbd was set to /system/core/adb instead of
/external/boringssl. This caused a problem that NOTICE file in
/external/boringssl is not tagged to libconscrypt, but the NOTICE file
for adbd is.
Fixing the problem by recording the module directories of the included
modules and emitting it in LOCAL_PATH.
Bug: 145347092
Test: Settings -> About Phone -> Legal Information -> Third-party
license. The license for /apex/com.android.adbd/lib64/libconscrypt.so is
OpenSSL.
Change-Id: I76f1830d5a10af63fa74dcc2a42730ffabb8c4ed
Use the empty string for the core image variant so that modules
added to imageMutator do not change their build directory.
Bug: 142286466
Test: m checkbuild
Change-Id: Ida4534d9a4d6176236aaa480fed359ce27acfaa1
Merged-In: Ida4534d9a4d6176236aaa480fed359ce27acfaa1
(cherry picked from commit 72d685ee7f45e5393be44ae4159edf083ac918de)
When LOCAL_COPY_HEADER lines are removed, we just removed the copy rule,
we didn't actually remove the old header, so C/C++ files could still
include the old headers during incremental builds.
While we do consider LOCAL_COPY_HEADERS as near-obsolet, and it'll
disappear as we move everything over to Soong, this could produce some
unfortunate incremental build results while people are attempting to
remove them.
Fix this by ensuring that only the files currently listed in
LOCAL_COPY_HEADERS exist in TARGET_OUT_HEADERS after we run Kati.
Test: Remove a LOCAL_COPY_HEADERS entry; see the header removed
Change-Id: I817305703a6996d50490d552623d7df019b608c9
