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9ba55921
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2021-03-05T10:07:30
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Static tramp v5 (#624)
* Static Trampolines
Closure Trampoline Security Issue
=================================
Currently, the trampoline code used in libffi is not statically defined in
a source file (except for MACH). The trampoline is either pre-defined
machine code in a data buffer. Or, it is generated at runtime. In order to
execute a trampoline, it needs to be placed in a page with executable
permissions.
Executable data pages are attack surfaces for attackers who may try to
inject their own code into the page and contrive to have it executed. The
security settings in a system may prevent various tricks used in user land
to write code into a page and to have it executed somehow. On such systems,
libffi trampolines would not be able to run.
Static Trampoline
=================
To solve this problem, the trampoline code needs to be defined statically
in a source file, compiled and placed in the text segment so it can be
mapped and executed naturally without any tricks. However, the trampoline
needs to be able to access the closure pointer at runtime.
PC-relative data referencing
============================
The solution implemented in this patch set uses PC-relative data references.
The trampoline is mapped in a code page. Adjacent to the code page, a data
page is mapped that contains the parameters of the trampoline:
- the closure pointer
- pointer to the ABI handler to jump to
The trampoline code uses an offset relative to its current PC to access its
data.
Some architectures support PC-relative data references in the ISA itself.
E.g., X64 supports RIP-relative references. For others, the PC has to
somehow be loaded into a general purpose register to do PC-relative data
referencing. To do this, we need to define a get_pc() kind of function and
call it to load the PC in a desired register.
There are two cases:
1. The call instruction pushes the return address on the stack.
In this case, get_pc() will extract the return address from the stack
and load it in the desired register and return.
2. The call instruction stores the return address in a designated register.
In this case, get_pc() will copy the return address to the desired
register and return.
Either way, the PC next to the call instruction is obtained.
Scratch register
================
In order to do its job, the trampoline code would need to use a scratch
register. Depending on the ABI, there may not be a register available for
scratch. This problem needs to be solved so that all ABIs will work.
The trampoline will save two values on the stack:
- the closure pointer
- the original value of the scratch register
This is what the stack will look like:
sp before trampoline ------> --------------------
| closure pointer |
--------------------
| scratch register |
sp after trampoline -------> --------------------
The ABI handler can do the following as needed by the ABI:
- the closure pointer can be loaded in a desired register
- the scratch register can be restored to its original value
- the stack pointer can be restored to its original value
(the value when the trampoline was invoked)
To do this, I have defined prolog code for each ABI handler. The legacy
trampoline jumps to the ABI handler directly. But the static trampoline
defined in this patch jumps tp the prolog code which performs the above
actions before jumping to the ABI handler.
Trampoline Table
================
In order to reduce the trampoline memory footprint, the trampoline code
would be defined as a code array in the text segment. This array would be
mapped into the address space of the caller. The mapping would, therefore,
contain a trampoline table.
Adjacent to the trampoline table mapping, there will be a data mapping that
contains a parameter table, one parameter block for each trampoline. The
parameter block will contain:
- a pointer to the closure
- a pointer to the ABI handler
The static trampoline code would finally look like this:
- Make space on the stack for the closure and the scratch register
by moving the stack pointer down
- Store the original value of the scratch register on the stack
- Using PC-relative reference, get the closure pointer
- Store the closure pointer on the stack
- Using PC-relative reference, get the ABI handler pointer
- Jump to the ABI handler
Mapping size
============
The size of the code mapping that contains the trampoline table needs to be
determined on a per architecture basis. If a particular architecture
supports multiple base page sizes, then the largest supported base page size
needs to be chosen. E.g., we choose 16K for ARM64.
Trampoline allocation and free
==============================
Static trampolines are allocated in ffi_closure_alloc() and freed in
ffi_closure_free().
Normally, applications use these functions. But there are some cases out
there where the user of libffi allocates and manages its own closure
memory. In such cases, static trampolines cannot be used. These will
fall back to using legacy trampolines. The user has to make sure that
the memory is executable.
ffi_closure structure
=====================
I did not want to make any changes to the size of the closure structure for
this feature to guarantee compatibility. But the opaque static trampoline
handle needs to be stored in the closure. I have defined it as follows:
- char tramp[FFI_TRAMPOLINE_SIZE];
+ union {
+ char tramp[FFI_TRAMPOLINE_SIZE];
+ void *ftramp;
+ };
If static trampolines are used, then tramp[] is not needed to store a
dynamic trampoline. That space can be reused to store the handle. Hence,
the union.
Architecture Support
====================
Support has been added for x64, i386, aarch64 and arm. Support for other
architectures can be added very easily in the future.
OS Support
==========
Support has been added for Linux. Support for other OSes can be added very
easily.
Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
* x86: Support for Static Trampolines
- Define the arch-specific initialization function ffi_tramp_arch ()
that returns trampoline size information to common code.
- Define the trampoline code mapping and data mapping sizes.
- Define the trampoline code table statically. Define two tables,
actually, one with CET and one without.
- Introduce a tiny prolog for each ABI handling function. The ABI
handlers addressed are:
- ffi_closure_unix64
- ffi_closure_unix64_sse
- ffi_closure_win64
The prolog functions are called:
- ffi_closure_unix64_alt
- ffi_closure_unix64_sse_alt
- ffi_closure_win64_alt
The legacy trampoline jumps to the ABI handler. The static
trampoline jumps to the prolog function. The prolog function uses
the information provided by the static trampoline, sets things up
for the ABI handler and then jumps to the ABI handler.
- Call ffi_tramp_set_parms () in ffi_prep_closure_loc () to
initialize static trampoline parameters.
Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
* i386: Support for Static Trampolines
- Define the arch-specific initialization function ffi_tramp_arch ()
that returns trampoline size information to common code.
- Define the trampoline code table statically. Define two tables,
actually, one with CET and one without.
- Define the trampoline code table statically.
- Introduce a tiny prolog for each ABI handling function. The ABI
handlers addressed are:
- ffi_closure_i386
- ffi_closure_STDCALL
- ffi_closure_REGISTER
The prolog functions are called:
- ffi_closure_i386_alt
- ffi_closure_STDCALL_alt
- ffi_closure_REGISTER_alt
The legacy trampoline jumps to the ABI handler. The static
trampoline jumps to the prolog function. The prolog function uses
the information provided by the static trampoline, sets things up
for the ABI handler and then jumps to the ABI handler.
- Call ffi_tramp_set_parms () in ffi_prep_closure_loc () to
initialize static trampoline parameters.
Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
* arm64: Support for Static Trampolines
- Define the arch-specific initialization function ffi_tramp_arch ()
that returns trampoline size information to common code.
- Define the trampoline code mapping and data mapping sizes.
- Define the trampoline code table statically.
- Introduce a tiny prolog for each ABI handling function. The ABI
handlers addressed are:
- ffi_closure_SYSV
- ffi_closure_SYSV_V
The prolog functions are called:
- ffi_closure_SYSV_alt
- ffi_closure_SYSV_V_alt
The legacy trampoline jumps to the ABI handler. The static
trampoline jumps to the prolog function. The prolog function uses
the information provided by the static trampoline, sets things up
for the ABI handler and then jumps to the ABI handler.
- Call ffi_tramp_set_parms () in ffi_prep_closure_loc () to
initialize static trampoline parameters.
Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
* arm: Support for Static Trampolines
- Define the arch-specific initialization function ffi_tramp_arch ()
that returns trampoline size information to common code.
- Define the trampoline code mapping and data mapping sizes.
- Define the trampoline code table statically.
- Introduce a tiny prolog for each ABI handling function. The ABI
handlers addressed are:
- ffi_closure_SYSV
- ffi_closure_VFP
The prolog functions are called:
- ffi_closure_SYSV_alt
- ffi_closure_VFP_alt
The legacy trampoline jumps to the ABI handler. The static
trampoline jumps to the prolog function. The prolog function uses
the information provided by the static trampoline, sets things up
for the ABI handler and then jumps to the ABI handler.
- Call ffi_tramp_set_parms () in ffi_prep_closure_loc () to
initialize static trampoline parameters.
Signed-off-by: Madhavan T. Venkataraman <madvenka@linux.microsoft.com>
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c78fcf88
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2020-10-27T07:02:36
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Removing unnecessary instruction from ffi_call_unix64 (#588)
unix64.S's `ffi_call_unix64` looks like it used to take six parameters,
where the sixth said the number of SSE register arguments. However,
currently the function only takes five parameters, and the number of SSE
register arguments is encoded in the `struct register_args *` passed as
the first parameter to `ffi_call_unix64`. This change removes an
instruction that tries to use this missing sixth parameter as the number
of SSE arguments.
This fix should not change any behavior, nor fix any bugs, because a few
instructions later the value moved from %r9d into %eax is overwritten by
the correct value anyway. This change merely makes the code a tad less
confusing, because currently the assembly moves from a register (r9)
whose value is never set.
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78556561
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2020-02-21T19:08:06
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x86: Add indirect branch tracking support (#540)
Intel Control-flow Enforcement Technology (CET):
https://software.intel.com/en-us/articles/intel-sdm
contains shadow stack (SHSTK) and indirect branch tracking (IBT). When
CET is enabled, ELF object files must be marked with .note.gnu.property
section. When Intel CET is enabled, include <cet.h> in assembly codes
to mark Intel CET support.
Also when IBT is enabled, all indirect branch targets must start with
ENDBR instruction and notrack prefix can be used to disable IBT on
indirect branch. <cet.h> defines _CET_ENDBR which can be used in
assembly codes for ENDBR instruction. If <cet.h> isn't included,
define _CET_ENDBR as empty so that _CET_ENDBR can be used in assembly
codes.
Trampoline must be enlarged to add ENDBR instruction unconditionally,
which is NOP on non-CET processors. This is required regardless if
libffi is enabled with CET since libffi.so will be marked in legacy
bitmap, but trampoline won't. Update library version for larger
FFI_TRAMPOLINE_SIZE.
This fixed:
https://github.com/libffi/libffi/issues/474
Tested with
$ CC="gcc -Wl,-z,cet-report=error -fcf-protection" CXX="g++ -Wl,-z,cet-report=error -fcf-protection" .../configure
on Linux CET machines in i686, x32 and x86-64 modes.
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65da63ab
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2018-06-25T04:38:58
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Add compact unwind for darwin/i386 (#440)
* x86: Add implementation of compact unwind for ffi_call_i386, et al.
Signed-off-by: Jeremy Huddleston Sequoia <jeremyhu@macports.org>
* x86: Use __text as the section name to avoid deprecated section name warnings.
Signed-off-by: Jeremy Huddleston Sequoia <jeremyhu@macports.org>
* darwin: Add missing regular,debug attributes for compact unwind sections
Signed-off-by: Jeremy Huddleston Sequoia <jeremyhu@macports.org>
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1d704051
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2018-06-17T17:01:50
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i386: Fix missing break; in case statement leading to incorrectly returned FFI_BAD_ABI (#437)
* i386: Add missing break triggering dead store static analyzer checks.
Register calling sequence is being reported as bad ABI instead of working as intended.
Found-by: Clang Static Analysis
Signed-off-by: Jeremy Huddleston Sequoia <jeremyhu@macports.org>
* Mark ffi arm sysv entry points as private_extern.
Signed-off-by: Jeremy Huddleston Sequoia <jeremyhu@macports.org>
* x86_64: Add implementation of compact unwind for ffi_call_unix64.
Signed-off-by: Jeremy Huddleston Sequoia <jeremyhu@apple.com>
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b5ee3957
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2018-05-05T07:41:53
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Revert "Remove some symbol exports and cleanup newline warnings (#433)"
This reverts commit a5a0f3cf36dfb4d64316414a872288c3170e6c1d.
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a5a0f3cf
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2018-05-05T03:44:33
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Remove some symbol exports and cleanup newline warnings (#433)
* build: Ensure darwin generated sources end with a new line
Signed-off-by: Jeremy Huddleston Sequoia <jeremyhu@macports.org>
* build: Use .private_extern where missing to prevent exporting symbols that are not API
Signed-off-by: Jeremy Huddleston Sequoia <jeremyhu@macports.org>
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d15581c6
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2017-12-01T00:34:30
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Updating calls to ffi_closure_unix64_inner and ffi_closure_win64_inner to use PLT. Without this fix, statically linking libffi causes the linker error i.e. 'requires dynamic R_X86_64_PC32 reloc against ffi_closure_unix64_inner which may overflow at runtime; recompile with -fPIC)'
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eaa59755
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2015-07-26T17:17:16
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src/x86/win64.S: Handle name mangling and PIC
Move the macros from unix64.S into a shared header asmnames.h and use
them in win64.S too.
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f1560b7b
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2015-01-16T11:31:37
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x86: Solaris fixes
* Solaris/x86 /bin/as doesn't support .org, so I've just disabled the
uses in src/x86/{sysv, unix64}.S, as on Darwin.
* Solaris/x86 needs to use EH_FRAME_FLAGS so manually and compiler
generated .eh_frame sections match, otherwise libffi.so fails to link:
* Solaris/x86 /bin/as has different COMDAT syntax; I've disabled it for
the moment.
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ae842a51
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2014-11-25T11:43:40
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x86: More Darwin unwind fixups
EHFrame{N} IIRC is a special cue to ld64 that it should treat the unwind
in the object as "special/legacy" .. [these days everything is .cfi_xxxx
(except, cctools-as, as you noted)] .. without that much confusion arises
with ld64's atom-isation of the eh_frame section.
xxxx.eh labels are not needed for darwin ld64 >= 85.2.1 (i.e. darwin9,
xcode 3.1.4) to all intents and purposes, that's all that matters now,
since I think that anyone trying to build on 10.4/darwin8/xcode2.5 would
have to use a later ld64 (from odcctools) for other reasons.
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8fa3c9f2
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2014-11-25T09:27:54
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x86: Reinstate hand-written unwind info for unix64.S
One more try to get default Darwin to work.
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5f35e0ff
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2014-11-24T16:26:50
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x86: Avoid using gas local labels
Which are unsupported by Darwin cctools as.
Thankfully this doesn't uglify the source too much.
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042b8daf
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2014-11-24T11:24:02
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x86: Use .balign not .align
The Apple assembler defaults to power of two alignment, rather than
byte alignment like everyone else. Force byte alignment by using
the proper directive.
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0172bc02
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2014-11-24T10:42:02
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x86: Disable .org for Darwin
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9f112619
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2014-11-22T20:02:43
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x86: Best guess at update for Darwin
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0e303c06
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2014-11-12T03:58:58
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x86: Work around clang bugs
http://llvm.org/bugs/show_bug.cgi?21500
http://llvm.org/bugs/show_bug.cgi?21501
http://llvm.org/bugs/show_bug.cgi?21515
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610c90bf
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2014-10-28T11:21:50
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x86_64: Add support for complex types
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32c56831
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2014-10-28T11:17:35
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x86_64: Decouple return types from FFI_TYPE constants
We can better support structure returns, and as prep for
complex types.
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2e9dc165
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2014-10-27T13:41:39
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x86_64: Fixups for x32
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6b62fb4a
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2014-10-17T11:11:58
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x86-64: Support go closures
Dumps all of the hand-coded unwind info for gas generated. Move jump
table data into .rodata. Adjust ffi_call_unix64 to load the static
chain. Split out sse portions of ffi_closure_unix64 to
ffi_closure_unix64_sse rather than test cif->flags at runtime.
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fd07c9e4
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2013-02-07T18:00:36
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Add cache flushing routine for sun compiler on sparc solaris 2.8
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35ddb69c
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2013-01-08T07:53:37
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Only emit DWARF unwind info when building with GCC
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3f5b1375
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2010-07-12T14:39:18
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rebase
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c6dddbd0
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2009-10-04T08:11:33
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Initial commit
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