Revert the names used in the BoringSSL C/asm code to the names used in
BoringSSL. This substantially reduces the diff between *ring* and
BoringSSL for these files.
Use a variant of BoringSSL's symbol prefixing machinery to semi-
automatically prefix FFI symbols with the `GFp_` prefix. The names aren't
all exactly the same as before, because previously we *replaced* a
symbol's original prefix with the `GFp_` prefix; now we're prepending
`GFp_`. In the future we'll use a different prefix entirely.
This paves the way for using different prefixes for each version so that
multiple versions of *ring* can be linked into an executable at once.
This change adds optional support for
- Armv8.3-A Pointer Authentication (PAuth) and
- Armv8.5-A Branch Target Identification (BTI)
features to the perl scripts.
Both features can be enabled with additional compiler flags.
Unless any of these are enabled explicitly there is no code change at
all.
The extensions are briefly described below. Please read the appropriate
chapters of the Arm Architecture Reference Manual for the complete
specification.
Scope
-----
This change only affects generated assembly code.
Armv8.3-A Pointer Authentication
--------------------------------
Pointer Authentication extension supports the authentication of the
contents of registers before they are used for indirect branching
or load.
PAuth provides a probabilistic method to detect corruption of register
values. PAuth signing instructions generate a Pointer Authentication
Code (PAC) based on the value of a register, a seed and a key.
The generated PAC is inserted into the original value in the register.
A PAuth authentication instruction recomputes the PAC, and if it matches
the PAC in the register, restores its original value. In case of a
mismatch, an architecturally unmapped address is generated instead.
With PAuth, mitigation against ROP (Return-oriented Programming) attacks
can be implemented. This is achieved by signing the contents of the
link-register (LR) before it is pushed to stack. Once LR is popped,
it is authenticated. This way a stack corruption which overwrites the
LR on the stack is detectable.
The PAuth extension adds several new instructions, some of which are not
recognized by older hardware. To support a single codebase for both pre
Armv8.3-A targets and newer ones, only NOP-space instructions are added
by this patch. These instructions are treated as NOPs on hardware
which does not support Armv8.3-A. Furthermore, this patch only considers
cases where LR is saved to the stack and then restored before branching
to its content. There are cases in the code where LR is pushed to stack
but it is not used later. We do not address these cases as they are not
affected by PAuth.
There are two keys available to sign an instruction address: A and B.
PACIASP and PACIBSP only differ in the used keys: A and B, respectively.
The keys are typically managed by the operating system.
To enable generating code for PAuth compile with
-mbranch-protection=<mode>:
- standard or pac-ret: add PACIASP and AUTIASP, also enables BTI
(read below)
- pac-ret+b-key: add PACIBSP and AUTIBSP
Armv8.5-A Branch Target Identification
--------------------------------------
Branch Target Identification features some new instructions which
protect the execution of instructions on guarded pages which are not
intended branch targets.
If Armv8.5-A is supported by the hardware, execution of an instruction
changes the value of PSTATE.BTYPE field. If an indirect branch
lands on a guarded page the target instruction must be one of the
BTI <jc> flavors, or in case of a direct call or jump it can be any
other instruction. If the target instruction is not compatible with the
value of PSTATE.BTYPE a Branch Target Exception is generated.
In short, indirect jumps are compatible with BTI <j> and <jc> while
indirect calls are compatible with BTI <c> and <jc>. Please refer to the
specification for the details.
Armv8.3-A PACIASP and PACIBSP are implicit branch target
identification instructions which are equivalent with BTI c or BTI jc
depending on system register configuration.
BTI is used to mitigate JOP (Jump-oriented Programming) attacks by
limiting the set of instructions which can be jumped to.
BTI requires active linker support to mark the pages with BTI-enabled
code as guarded. For ELF64 files BTI compatibility is recorded in the
.note.gnu.property section. For a shared object or static binary it is
required that all linked units support BTI. This means that even a
single assembly file without the required note section turns-off BTI
for the whole binary or shared object.
The new BTI instructions are treated as NOPs on hardware which does
not support Armv8.5-A or on pages which are not guarded.
To insert this new and optional instruction compile with
-mbranch-protection=standard (also enables PAuth) or +bti.
When targeting a guarded page from a non-guarded page, weaker
compatibility restrictions apply to maintain compatibility between
legacy and new code. For detailed rules please refer to the Arm ARM.
Compiler support
----------------
Compiler support requires understanding '-mbranch-protection=<mode>'
and emitting the appropriate feature macros (__ARM_FEATURE_BTI_DEFAULT
and __ARM_FEATURE_PAC_DEFAULT). The current state is the following:
-------------------------------------------------------
| Compiler | -mbranch-protection | Feature macros |
+----------+---------------------+--------------------+
| clang | 9.0.0 | 11.0.0 |
+----------+---------------------+--------------------+
| gcc | 9 | expected in 10.1+ |
-------------------------------------------------------
Available Platforms
------------------
Arm Fast Model and QEMU support both extensions.
https://developer.arm.com/tools-and-software/simulation-models/fast-modelshttps://www.qemu.org/
Implementation Notes
--------------------
This change adds BTI landing pads even to assembly functions which are
likely to be directly called only. In these cases, landing pads might
be superfluous depending on what code the linker generates.
Code size and performance impact for these cases would be negligble.
Interaction with C code
-----------------------
Pointer Authentication is a per-frame protection while Branch Target
Identification can be turned on and off only for all code pages of a
whole shared object or static binary. Because of these properties if
C/C++ code is compiled without any of the above features but assembly
files support any of them unconditionally there is no incompatibility
between the two.
Useful Links
------------
To fully understand the details of both PAuth and BTI it is advised to
read the related chapters of the Arm Architecture Reference Manual
(Arm ARM):
https://developer.arm.com/documentation/ddi0487/latest/
Additional materials:
"Providing protection for complex software"
https://developer.arm.com/architectures/learn-the-architecture/providing-protection-for-complex-software
Arm Compiler Reference Guide Version 6.14: -mbranch-protection
https://developer.arm.com/documentation/101754/0614/armclang-Reference/armclang-Command-line-Options/-mbranch-protection?lang=en
Arm C Language Extensions (ACLE)
https://developer.arm.com/docs/101028/latest
Change-Id: I4335f92e2ccc8e209c7d68a0a79f1acdf3aeb791
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/42084
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>
When running the ARM perlasm files on Windows, close STDOUT fails. There
appears to be some weird quirk on Windows when one replaces STDOUT with
a pipe. The x86_64.pl files all avoid this by opening OUT and then
setting *STDOUT=*OUT. Align all the ARM files with that pattern.
See https://ci.appveyor.com/project/conscrypt/conscrypt
Change-Id: Ibee9427a05d806f7f23a6d9817394cfabf2f534a
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/37324
Reviewed-by: Kenny Root <kroot@google.com>
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>
If the xlate filter script fails, the outer script swallows the error,
unless we check the return value of close.
Change-Id: Ib506bb745a5d27b9d1df9329535bf81ad090f41f
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/35724
Reviewed-by: Adam Langley <agl@google.com>
This makes AES-GCM always constant-time on aarch64 (provided assembly is
enabled). Unlike vpaes, this does come at a binary size penalty of 1K
compared to the gcm_*_4bit version.
ABI testing already covered by GCMTest.ABI (GHASH_ASM_ARM covers both
OPENSSL_ARM and OPENSSL_AARCH64.)
Cortex-A53 (Raspberry Pi 3 Model B+)
Before:
Did 274000 AES-128-GCM (16 bytes) seal operations in 1003461us (273055.0 ops/sec): 4.4 MB/s
Did 53000 AES-128-GCM (256 bytes) seal operations in 1007689us (52595.6 ops/sec): 13.5 MB/s
Did 12000 AES-128-GCM (1350 bytes) seal operations in 1075908us (11153.4 ops/sec): 15.1 MB/s
Did 2068 AES-128-GCM (8192 bytes) seal operations in 1089037us (1898.9 ops/sec): 15.6 MB/s
After:
Did 298000 AES-128-GCM (16 bytes) seal operations in 1002917us (297133.3 ops/sec): 4.8 MB/s
Did 64000 AES-128-GCM (256 bytes) seal operations in 1001124us (63928.1 ops/sec): 16.4 MB/s
Did 14000 AES-128-GCM (1350 bytes) seal operations in 1015477us (13786.6 ops/sec): 18.6 MB/s
Did 2497 AES-128-GCM (8192 bytes) seal operations in 1057951us (2360.2 ops/sec): 19.3 MB/s
Bug: 265
Change-Id: I251bf0f2eae0578580bb14192755e5d8ff64cd14
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/35285
Reviewed-by: Adam Langley <agl@google.com>
