Add Zicfiss extension #377
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Just letting you know I am away on Holiday until early January, so it might take me a while before I can go through this in detail. |
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- Separate legalizers for menvcfg and senvcfg - Add a getter for senvcfg as fields in senvcfg depend on menvcfg
Zicfiss instructions use codepoints defined by Zimop/Zcmop extension. Add the baseline Zimop/Zcmop as preparation to be extended by Zicfiss.
- SSE field in menvcfg - SSE field in senvcfg - New CSR ssp
- Zicfiss instructions can generate software check exceptions with xtval set to SHADOW_STACK_FAULT.
With Zicfiss, PTE based checks may cause a page-fault or an access fault. Extend the PTE permission checks plumbing to be able to signal both.
- SS pages are encoded in pte as XWR=010b. - Add rules for access to such pages by non-SS load/store/AMO and inst. fetch. - Add rules for access to such pages by SS load/store/AMO. - SS access not allowed in Svbare. When virtual memory system is not active, all shadow stack accesses cause an access violation. - Add rules for PMP access checks by shadow stack accesses
- Some zimop and zcmop codepoints may be used by extensions such as Zicfiss. Add generic infrastructure to support this.
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- Add sspush/sspopchk/ssrdp/ssamoswap - Add c_sspush/c_sspopchk
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Specification: https://github.com/riscv/riscv-cfi/blob/main/cfi_backward.adoc
Tests: riscv-non-isa/riscv-arch-test#417
Includes the unratified Zimop and Zcmop extensions which Zicfiss depends on:
https://github.com/riscv/riscv-isa-manual/blob/main/src/zimop.adoc
Parts of the sw-check exception code is duplicated here and in PR #361