[aadwarf64] Add DWARF support for unwinding with FEAT_PAuth_LR enabled #245
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This introduces DWARF support to enable unwinders to authenticate return addresses signed using FEAT_PAuth_LR, where the value of PC is used as an extra diversifier. To achieve that, this proposes the following changes to the aadwarf64 document: * Expanding usage of the `RA_SIGN_STATE` pseudo-register, allocating it's bit[1] to indicate wether the value of PC has been used for return address signing. * Introducing a new vendor call frame instruction, `DW_CFA_AARCH64_negate_ra_state_with_pc`, which negates both bit[0] and bit[1] of `RA_SIGN_STATE` and instructs the unwinder to capture the current code location to be used when authenticating the return address. Co-authored-by: Oliver Stannard <oliver.stannard@arm.com>
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DanielKristofKiss
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Feb 26, 2024
Stylie777
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Oct 14, 2024
This introduces support for unwinding programs where return addresses have been signed using FEAT_PAuth_Lr, where the value of PC is used as a diversifier (-mbranch-protection=pac-ret+pc). A new vendor specific call frame instruction is added, named `DW_CFA_AARCH64_negate_ra_state_with_pc`, to instruct the unwinder tocapture the value of PC at the point of signing and update bit 1 of the existing `RA_SIGN_STATE` pseudo-register to flag the need to use it for authentication. See ARM-software/abi-aa#245 for the ABI change. Authored-by: pratlucas <lucas.prates@arm.com>
Stylie777
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This introduces compiler and dwarfdump support for emitting and parsing the new `DW_CFA_AARCH64_negate_ra_state_with_pc` DWARF instruction for FEAT_PAuth_LR. This does mean that, when using FEAT_PAuthLR, the improvements introduced in llvm#96337 cannot be utilised. `.cfi_negate_ra_state_with_pc` must be emitted directly after the signing instruction, and when bundled with other CFI calls, leads to faults when running a program. There are no changes seen when not using FEAT_PAuthLR to how the CFI Instructions are generated. See ARM-software/abi-aa#245 for the ABI change that incororates FEAT_PAuthLR. Authored-by: pratlucas <lucas.prates@arm.com> Co-authored by: vhscampos <victor.campos@arm.com> Co-authored by: Stylie777 <jack.styles@arm.com>
Stylie777
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Oct 16, 2024
This introduces support for unwinding programs where return addresses have been signed using FEAT_PAuth_Lr, where the value of PC is used as a diversifier (-mbranch-protection=pac-ret+pc). A new vendor specific call frame instruction is added, named `DW_CFA_AARCH64_negate_ra_state_with_pc`, to instruct the unwinder tocapture the value of PC at the point of signing and update bit 1 of the existing `RA_SIGN_STATE` pseudo-register to flag the need to use it for authentication. See ARM-software/abi-aa#245 for the ABI change. Authored-by: pratlucas <lucas.prates@arm.com>
Stylie777
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Oct 16, 2024
This introduces compiler and dwarfdump support for emitting and parsing the new `DW_CFA_AARCH64_negate_ra_state_with_pc` DWARF instruction for FEAT_PAuth_LR. This does mean that, when using FEAT_PAuthLR, the improvements introduced in llvm#96337 cannot be utilised. `.cfi_negate_ra_state_with_pc` must be emitted directly after the signing instruction, and when bundled with other CFI calls, leads to faults when running a program. There are no changes seen when not using FEAT_PAuthLR to how the CFI Instructions are generated. See ARM-software/abi-aa#245 for the ABI change that incororates FEAT_PAuthLR. Authored-by: pratlucas <lucas.prates@arm.com> Co-authored by: vhscampos <victor.campos@arm.com> Co-authored by: Stylie777 <jack.styles@arm.com>
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This introduces DWARF support to enable unwinders to authenticate return
addresses signed using FEAT_PAuth_LR, where the value of PC is used as
an extra diversifier.
To achieve that, this proposes the following changes to the aadwarf64
document:
RA_SIGN_STATEpseudo-register, allocatingit's bit[1] to indicate wether the value of PC has been used for
return address signing.
DW_CFA_AARCH64_negate_ra_state_with_pc, which negates both bit[0]and bit[1] of
RA_SIGN_STATEand instructs the unwinder to capturethe current code location to be used when authenticating the return
address.
Co-authored-by: Oliver Stannard oliver.stannard@arm.com