UPSTREAM PR #30501: riscv: Add lpad instructions for CFI support#678
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UPSTREAM PR #30501: riscv: Add lpad instructions for CFI support#678loci-dev wants to merge 2 commits into
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Add 'lpad 0' (landing pad) instructions at the beginning of all RISC-V assembly functions to support Forward Control Flow Integrity (Zicfilp extension). The lpad instruction is encoded as AUIPC x0, <lpl>, which is harmless on hardware without Zicfilp support (writes to zero register) and provides CFI protection on hardware with Zicfilp support. The instruction encoding (0x00000017 | (lpl << 12)) is directly emitted as .word, making it compatible with all toolchains.
Implement correct placement policy for lpad (landing pad) instructions according to RISC-V Zicfilp specification: - Add lpad ONLY to global symbols (exported functions) - Remove lpad from local labels (internal jump targets) Signed-off-by: Phoebe Chen <phoebe.chen@sifive.com>
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Source pull request: openssl/openssl#30501
Add 'lpad 0' (landing pad) instructions at the beginning of all RISC-V assembly functions to support Forward Control Flow Integrity (Zicfilp extension).
The lpad instruction is encoded as
AUIPC x0, <lpl>, which is harmless on hardware without Zicfilp support (writes to zero register) and provides CFI protection on hardware with Zicfilp support.The instruction encoding
(0x00000017 | (lpl << 12))is directly emitted as .word, making it compatible with all toolchains.