| Message ID | 20231114022254.294711-1-alvinga@andestech.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v5] target/riscv: update checks on writing pmpcfg for Smepmp to version 1.0 | expand |
On Tue, Nov 14, 2023 at 12:24 PM Alvin Chang via <qemu-devel@nongnu.org> wrote: > > Current checks on writing pmpcfg for Smepmp follows Smepmp version > 0.9.1. However, Smepmp specification has already been ratified, and > there are some differences between version 0.9.1 and 1.0. In this > commit we update the checks of writing pmpcfg to follow Smepmp version > 1.0. > > When mseccfg.MML is set, the constraints to modify PMP rules are: > 1. Locked rules cannot be removed or modified until a PMP reset, unless > mseccfg.RLB is set. > 2. From Smepmp specification version 1.0, chapter 2 section 4b: > Adding a rule with executable privileges that either is M-mode-only > or a locked Shared-Region is not possible and such pmpcfg writes are > ignored, leaving pmpcfg unchanged. > > The commit transfers the value of pmpcfg into the index of the Smepmp > truth table, and checks the rules by aforementioned specification > changes. > > Signed-off-by: Alvin Chang <alvinga@andestech.com> > --- > Changes from v4: Rebase on master. > > Changes from v3: Modify "epmp_operation" to "smepmp_operation". > > Changes from v2: Adopt switch case ranges and numerical order. > > Changes from v1: Convert ePMP over to Smepmp. > > target/riscv/pmp.c | 40 ++++++++++++++++++++++++++++++++-------- > 1 file changed, 32 insertions(+), 8 deletions(-) > > diff --git a/target/riscv/pmp.c b/target/riscv/pmp.c > index 162e88a90a..4069514069 100644 > --- a/target/riscv/pmp.c > +++ b/target/riscv/pmp.c > @@ -102,16 +102,40 @@ static bool pmp_write_cfg(CPURISCVState *env, uint32_t pmp_index, uint8_t val) > locked = false; > } > > - /* mseccfg.MML is set */ > - if (MSECCFG_MML_ISSET(env)) { > - /* not adding execute bit */ > - if ((val & PMP_LOCK) != 0 && (val & PMP_EXEC) != PMP_EXEC) { > + /* > + * mseccfg.MML is set. Locked rules cannot be removed or modified > + * until a PMP reset. Besides, from Smepmp specification version 1.0 > + * , chapter 2 section 4b says: > + * Adding a rule with executable privileges that either is > + * M-mode-only or a locked Shared-Region is not possible and such > + * pmpcfg writes are ignored, leaving pmpcfg unchanged. > + */ > + if (MSECCFG_MML_ISSET(env) && !pmp_is_locked(env, pmp_index)) { This is tricky and took me a while to get my head around. From what I can tell, there is a bug in the spec. The spec specifically states that: """ The meaning of pmpcfg.L changes: Instead of marking a rule as locked and enforced in all modes, it now marks a rule as M-mode-only when set and S/U-mode-only when unset. """ So the check for !pmp_is_locked() sounds correct. But then they add: """ The formerly reserved encoding of pmpcfg.RW=01, and the encoding pmpcfg.LRWX=1111, now encode a Shared-Region. """ Which contradicts what they just said. I *think* we want to ignore the locked bit here. We don't actually care if it's already set, instead we care if the region is an M-mode only region from the 2.1 table I think the best bet here is to create a helper function that takes a pmpcfg value and returns if it is M-mode only. Then we should check if the current pmp_index is M-mode only OR if we are adding one and then reject that. Does that make sense? Alistair > + /* > + * Convert the PMP permissions to match the truth table in the > + * Smepmp spec. > + */ > + const uint8_t smepmp_operation = > + ((val & PMP_LOCK) >> 4) | ((val & PMP_READ) << 2) | > + (val & PMP_WRITE) | ((val & PMP_EXEC) >> 2); > + > + switch (smepmp_operation) { > + case 0 ... 8: > locked = false; > - } > - /* shared region and not adding X bit */ > - if ((val & PMP_LOCK) != PMP_LOCK && > - (val & 0x7) != (PMP_WRITE | PMP_EXEC)) { > + break; > + case 9 ... 11: > + break; > + case 12: > + locked = false; > + break; > + case 13: > + break; > + case 14: > + case 15: > locked = false; > + break; > + default: > + g_assert_not_reached(); > } > } > } else { > -- > 2.34.1 > >
diff --git a/target/riscv/pmp.c b/target/riscv/pmp.c index 162e88a90a..4069514069 100644 --- a/target/riscv/pmp.c +++ b/target/riscv/pmp.c @@ -102,16 +102,40 @@ static bool pmp_write_cfg(CPURISCVState *env, uint32_t pmp_index, uint8_t val) locked = false; } - /* mseccfg.MML is set */ - if (MSECCFG_MML_ISSET(env)) { - /* not adding execute bit */ - if ((val & PMP_LOCK) != 0 && (val & PMP_EXEC) != PMP_EXEC) { + /* + * mseccfg.MML is set. Locked rules cannot be removed or modified + * until a PMP reset. Besides, from Smepmp specification version 1.0 + * , chapter 2 section 4b says: + * Adding a rule with executable privileges that either is + * M-mode-only or a locked Shared-Region is not possible and such + * pmpcfg writes are ignored, leaving pmpcfg unchanged. + */ + if (MSECCFG_MML_ISSET(env) && !pmp_is_locked(env, pmp_index)) { + /* + * Convert the PMP permissions to match the truth table in the + * Smepmp spec. + */ + const uint8_t smepmp_operation = + ((val & PMP_LOCK) >> 4) | ((val & PMP_READ) << 2) | + (val & PMP_WRITE) | ((val & PMP_EXEC) >> 2); + + switch (smepmp_operation) { + case 0 ... 8: locked = false; - } - /* shared region and not adding X bit */ - if ((val & PMP_LOCK) != PMP_LOCK && - (val & 0x7) != (PMP_WRITE | PMP_EXEC)) { + break; + case 9 ... 11: + break; + case 12: + locked = false; + break; + case 13: + break; + case 14: + case 15: locked = false; + break; + default: + g_assert_not_reached(); } } } else {
Current checks on writing pmpcfg for Smepmp follows Smepmp version 0.9.1. However, Smepmp specification has already been ratified, and there are some differences between version 0.9.1 and 1.0. In this commit we update the checks of writing pmpcfg to follow Smepmp version 1.0. When mseccfg.MML is set, the constraints to modify PMP rules are: 1. Locked rules cannot be removed or modified until a PMP reset, unless mseccfg.RLB is set. 2. From Smepmp specification version 1.0, chapter 2 section 4b: Adding a rule with executable privileges that either is M-mode-only or a locked Shared-Region is not possible and such pmpcfg writes are ignored, leaving pmpcfg unchanged. The commit transfers the value of pmpcfg into the index of the Smepmp truth table, and checks the rules by aforementioned specification changes. Signed-off-by: Alvin Chang <alvinga@andestech.com> --- Changes from v4: Rebase on master. Changes from v3: Modify "epmp_operation" to "smepmp_operation". Changes from v2: Adopt switch case ranges and numerical order. Changes from v1: Convert ePMP over to Smepmp. target/riscv/pmp.c | 40 ++++++++++++++++++++++++++++++++-------- 1 file changed, 32 insertions(+), 8 deletions(-)