Skip to content

pmp: do not suppress pmpcfg writes for OFF or empty-range TOR entries under MML #2495

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
devtyagi3909 wants to merge 1 commit into
base: master
Choose a base branch
from
+21 −3
Open

pmp: do not suppress pmpcfg writes for OFF or empty-range TOR entries under MML #2495

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
24 changes: 21 additions & 3 deletions rtl/ibex_cs_registers.sv
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -161,11 +161,15 @@ module ibex_cs_registers import ibex_pkg::*, ibex_cheriot_pkg::*; #(

// Is a PMP config a locked one that allows M-mode execution when MSECCFG.MML is set (either
// M mode alone or shared M/U mode execution)?
//
// Returns 0 for A=OFF entries unconditionally: an OFF entry creates no PMP rule and therefore
// cannot grant M-mode execute access, regardless of the L and permission bits written.
// The write-suppression guard in Smepmp applies only to entries that would produce a valid rule.
function automatic logic is_mml_m_exec_cfg(ibex_pkg::pmp_cfg_t pmp_cfg);
logic unused_cfg = ^{pmp_cfg.mode};
logic value = 1'b0;

if (pmp_cfg.lock) begin
// A=OFF entries are inert; never suppress their writes.
if (pmp_cfg.lock && (pmp_cfg.mode != ibex_pkg::PMP_MODE_OFF)) begin
unique case ({pmp_cfg.read, pmp_cfg.write, pmp_cfg.exec})
3'b001, 3'b010, 3'b011, 3'b101: value = 1'b1;
default: value = 1'b0;
Expand Down Expand Up @@ -1463,11 +1467,25 @@ module ibex_cs_registers import ibex_pkg::*, ibex_cheriot_pkg::*; #(
assign pmp_cfg_locked[i] = pmp_cfg[i].lock & ~pmp_mseccfg_q.rlb;

// When MSECCFG.MML is set cannot add new regions allowing M mode execution unless MSECCFG.RLB
// is set
// is set. Suppression is skipped for:
// - A=OFF entries (is_mml_m_exec_cfg returns 0 after the function fix above)
// - A=TOR entries where pmpaddr[i-1] >= pmpaddr[i]: that range is empty and creates no rule.
// For region 0 the implicit base is 0; if pmpaddr[0]==0 the range is also empty.
logic tor_range_nonempty;
if (i == 0) begin : g_tor_base0
assign tor_range_nonempty = (pmp_cfg_wdata[i].mode == PMP_MODE_TOR) ?
(pmp_addr[i] != '0) : 1'b1;
end else begin : g_tor_base_prev
assign tor_range_nonempty = (pmp_cfg_wdata[i].mode == PMP_MODE_TOR) ?
(pmp_addr[i-1] < pmp_addr[i]) : 1'b1;
end

assign pmp_cfg_wr_suppress[i] = pmp_mseccfg_q.mml &
~pmp_mseccfg_q.rlb &
tor_range_nonempty &
is_mml_m_exec_cfg(pmp_cfg_wdata[i]);


// --------------------------
// Instantiate addr registers
// --------------------------
Expand Down
Loading