[PATCH v2 4/9] lib: sbi_hart: lock mwid CSR for RoT immutability
Yu-Chien Peter Lin <[email protected]>
| Newsgroups | org.infradead.lists.opensbi |
|---|---|
| Message-ID | <[email protected]> |
Lock the M-mode World ID (mwid) CSR during hart re-initialization to enforce immutability of the WID established by the root-of-trust. OpenSBI does not assign the WID value itself; it only sets MWID_LOCK to freeze the value established by prior RoT stage. The MWID_LOCK bit at XLEN-1 is sticky and makes the CSR read-only until reset, enforcing a temporal security boundary per the RISC-V Worlds specification. Signed-off-by: Yu-Chien Peter Lin <[email protected]> --- lib/sbi/sbi_hart.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/lib/sbi/sbi_hart.c b/lib/sbi/sbi_hart.c index f5f4062e..29856c0f 100644 --- a/lib/sbi/sbi_hart.c +++ b/lib/sbi/sbi_hart.c @@ -724,6 +724,13 @@ int sbi_hart_reinit(struct sbi_scratch *scratch) if (rc) return rc; + /* + * Assume MWID is restored by root-of-trust M-mode in previous + * stage. Lock mwid so RoT-defined WID remains immutable. + */ + if (sbi_hart_has_extension(scratch, SBI_HART_EXT_SMWID)) + csr_set(CSR_MWID, MWID_LOCK); + return 0; } -- 2.43.7 -- opensbi mailing list [email protected] http://lists.infradead.org/mailman/listinfo/opensbi