This patch is only a refactoring of the existing implementation
of PAuth and returned-address signing. The existing behavior is
preserved.
_Unwind_FrameState already contains several CIE and FDE information
(see the attributes below the comment "The information we care
about from the CIE/FDE" in libgcc/unwind-dw2.h).
The patch aims at moving the information from DWARF CIE (signing
key stored in the augmentation string) and FDE (the used signing
method) into _Unwind_FrameState along the already-stored CIE and
FDE information.
Note: those information have to be saved in frame_state_reg_info
instead of _Unwind_FrameState as they need to be savable by
DW_CFA_remember_state and restorable by DW_CFA_restore_state, that
both rely on the attribute "prev".
Those new information in _Unwind_FrameState simplifies the look-up
of the signing key when the return address is demangled. It also
allows future signing methods to be easily added.
_Unwind_FrameState is not a part of the public API of libunwind,
so the change is backward compatible.
A new architecture-specific handler MD_ARCH_EXTENSION_FRAME_INIT
allows to reset values (if needed) in the frame state and unwind
context before changing the frame state to the caller context.
A new architecture-specific handler MD_ARCH_EXTENSION_CIE_AUG_HANDLER
isolates the architecture-specific augmentation strings in AArch64
backend, and allows others architectures to reuse augmentation
strings that would have clashed with AArch64 DWARF extensions.
aarch64_demangle_return_addr, DW_CFA_AARCH64_negate_ra_state and
DW_CFA_val_expression cases in libgcc/unwind-dw2-execute_cfa.h
were documented to clarify where the value of the RA state register
is stored (FS and CONTEXT respectively).
libgcc/ChangeLog:
* config/aarch64/aarch64-unwind.h
(AARCH64_DWARF_RA_STATE_MASK): The mask for RA state register.
(aarch64_ra_signing_method_t): The diversifiers used to sign a
function's return address.
(aarch64_pointer_auth_key): The key used to sign a function's
return address.
(aarch64_cie_signed_with_b_key): Deleted as the signing key is
available now in _Unwind_FrameState.
(MD_ARCH_EXTENSION_CIE_AUG_HANDLER): New CIE augmentation string
handler for architecture extensions.
(MD_ARCH_EXTENSION_FRAME_INIT): New architecture-extension
initialization routine for DWARF frame state and context before
execution of DWARF instructions.
(aarch64_context_ra_state_get): Read RA state register from CONTEXT.
(aarch64_ra_state_get): Read RA state register from FS.
(aarch64_ra_state_set): Write RA state register into FS.
(aarch64_ra_state_toggle): Toggle RA state register in FS.
(aarch64_cie_aug_handler): Handler AArch64 augmentation strings.
(aarch64_arch_extension_frame_init): Initialize defaults for the
signing key (PAUTH_KEY_A), and RA state register (RA_no_signing).
(aarch64_demangle_return_addr): Rely on the frame registers and
the signing_key attribute in _Unwind_FrameState.
* unwind-dw2-execute_cfa.h:
Use the right alias DW_CFA_AARCH64_negate_ra_state for __aarch64__
instead of DW_CFA_GNU_window_save.
(DW_CFA_AARCH64_negate_ra_state): Save the signing method in RA
state register. Toggle RA state register without resetting 'how'
to REG_UNSAVED.
* unwind-dw2.c:
(extract_cie_info): Save the signing key in the current
_Unwind_FrameState while parsing the augmentation data.
(uw_frame_state_for): Reset some attributes related to architecture
extensions in _Unwind_FrameState.
(uw_update_context): Move authentication code to AArch64 unwinding.
* unwind-dw2.h (enum register_rule): Give a name to the existing
enum for the register rules, and replace 'unsigned char' by 'enum
register_rule' to facilitate debugging in GDB.
(_Unwind_FrameState): Add a new architecture-extension attribute
to store the signing key.
A recent change only initializes the regs.how[] during Dwarf unwinding
which resulted in an uninitialized offset used in return address signing
and random failures during unwinding. The fix is to encode the return
address signing state in REG_UNSAVED and a new state REG_UNSAVED_ARCHEXT.
libgcc/
PR target/107678
* unwind-dw2.h (REG_UNSAVED_ARCHEXT): Add new enum.
* unwind-dw2.c (uw_update_context_1): Add REG_UNSAVED_ARCHEXT case.
* unwind-dw2-execute_cfa.h: Use REG_UNSAVED_ARCHEXT/REG_UNSAVED to
encode the return address signing state.
* config/aarch64/aarch64-unwind.h (aarch64_demangle_return_addr)
Check current return address signing state.
(aarch64_frob_update_contex): Remove.
The parameters fs->data_align and fs->code_align always have fixed
values for a particular target in GCC-generated code. Specialize
execute_cfa_program for these values, to avoid multiplications.
gcc/c-family/
* c-cppbuiltin.cc (c_cpp_builtins): Define
__LIBGCC_DWARF_CIE_DATA_ALIGNMENT__.
libgcc/
* unwind-dw2-execute_cfa.h: New file. Extracted from
the execute_cfa_program function in unwind-dw2.c.
* unwind-dw2.c (execute_cfa_program_generic): New function.
(execute_cfa_program_specialized): Likewise.
(execute_cfa_program): Call execute_cfa_program_specialized
or execute_cfa_program_generic, as appropriate.
The parameters fs->data_align and fs->code_align always have fixed
values for a particular target in GCC-generated code. Specialize
execute_cfa_program for these values, to avoid multiplications.
gcc/c-family/
* c-cppbuiltin.cc (c_cpp_builtins): Define
__LIBGCC_DWARF_CIE_DATA_ALIGNMENT__.
libgcc/
* unwind-dw2-execute_cfa.h: New file. Extracted from
the execute_cfa_program function in unwind-dw2.c.
* unwind-dw2.c (execute_cfa_program_generic): New function.
(execute_cfa_program_specialized): Likewise.
(execute_cfa_program): Call execute_cfa_program_specialized
or execute_cfa_program_generic, as appropriate.
