[rtl,pmp] Allow all accesses to Debug Module in debug mode

andreaskurth · andreaskurth · commit 536142c556ff · 2024-12-13T14:04:45.000Z
The RISC-V Debug Specification (current release 1.0.0-rc4) in Section
A.2 states that the PMP must not disallow accesses to addresses of the
Debug Module when the hart is in debug mode, regardless of how the PMP
is configured.  This commit changes the PMP accordingly.

Signed-off-by: Andreas Kurth &lt;adk@lowrisc.org&gt;
diff --git a/dv/riscv_compliance/rtl/ibex_riscv_compliance.sv b/dv/riscv_compliance/rtl/ibex_riscv_compliance.sv
@@ -155,6 +155,8 @@ module ibex_riscv_compliance (
       .DbgTriggerEn     (DbgTriggerEn      ),
       .SecureIbex       (SecureIbex        ),
       .ICacheScramble   (ICacheScramble    ),
+      .DmBaseAddr       (32'h00000000      ),
+      .DmAddrMask       (32'h00000003      ),
       .DmHaltAddr       (32'h00000000      ),
       .DmExceptionAddr  (32'h00000000      )
     ) u_top (
diff --git a/dv/uvm/core_ibex/tb/core_ibex_tb_top.sv b/dv/uvm/core_ibex/tb/core_ibex_tb_top.sv
@@ -84,6 +84,8 @@ module core_ibex_tb_top;
   assign {scramble_key, scramble_nonce} = scrambling_key_if.d_data;
 
   ibex_top_tracing #(
+    .DmBaseAddr       (32'h`BOOT_ADDR       ),
+    .DmAddrMask       (32'h0000_0007        ),
     .DmHaltAddr       (32'h`BOOT_ADDR + 'h0 ),
     .DmExceptionAddr  (32'h`BOOT_ADDR + 'h4 ),
     .PMPEnable        (PMPEnable        ),
diff --git a/examples/simple_system/rtl/ibex_simple_system.sv b/examples/simple_system/rtl/ibex_simple_system.sv
@@ -204,6 +204,8 @@ module ibex_simple_system (
       .WritebackStage  ( WritebackStage   ),
       .BranchPredictor ( BranchPredictor  ),
       .DbgTriggerEn    ( DbgTriggerEn     ),
+      .DmBaseAddr      ( 32'h00100000     ),
+      .DmAddrMask      ( 32'h00000003     ),
       .DmHaltAddr      ( 32'h00100000     ),
       .DmExceptionAddr ( 32'h00100000     )
     ) u_top (
diff --git a/rtl/ibex_core.sv b/rtl/ibex_core.sv
@@ -44,6 +44,8 @@ module ibex_core import ibex_pkg::*; #(
   parameter int unsigned            RegFileDataWidth = 32,
   parameter bit                     MemECC           = 1'b0,
   parameter int unsigned            MemDataWidth     = MemECC ? 32 + 7 : 32,
+  parameter int unsigned            DmBaseAddr       = 32'h1A110000,
+  parameter int unsigned            DmAddrMask       = 32'h00000FFF,
   parameter int unsigned            DmHaltAddr       = 32'h1A110800,
   parameter int unsigned            DmExceptionAddr  = 32'h1A110808
 ) (
@@ -1177,6 +1179,8 @@ module ibex_core import ibex_pkg::*; #(
     assign pmp_priv_lvl[PMP_D]  = priv_mode_lsu;
 
     ibex_pmp #(
+      .DmBaseAddr    (DmBaseAddr),
+      .DmAddrMask    (DmAddrMask),
       .PMPGranularity(PMPGranularity),
       .PMPNumChan    (PMPNumChan),
       .PMPNumRegions (PMPNumRegions)
@@ -1185,6 +1189,7 @@ module ibex_core import ibex_pkg::*; #(
       .csr_pmp_cfg_i    (csr_pmp_cfg),
       .csr_pmp_addr_i   (csr_pmp_addr),
       .csr_pmp_mseccfg_i(csr_pmp_mseccfg),
+      .debug_mode_i     (debug_mode),
       .priv_mode_i      (pmp_priv_lvl),
       // Access checking channels
       .pmp_req_addr_i   (pmp_req_addr),
diff --git a/rtl/ibex_pmp.sv b/rtl/ibex_pmp.sv
@@ -5,6 +5,8 @@
 `include "dv_fcov_macros.svh"
 
 module ibex_pmp #(
+  parameter int unsigned DmBaseAddr     = 32'h1A110000,
+  parameter int unsigned DmAddrMask     = 32'h00000FFF,
   // Granularity of NAPOT access,
   // 0 = No restriction, 1 = 8 byte, 2 = 16 byte, 3 = 32 byte, etc.
   parameter int unsigned PMPGranularity = 0,
@@ -18,6 +20,8 @@ module ibex_pmp #(
   input  logic [33:0]             csr_pmp_addr_i    [PMPNumRegions],
   input  ibex_pkg::pmp_mseccfg_t  csr_pmp_mseccfg_i,
 
+  input  logic                    debug_mode_i,
+
   input  ibex_pkg::priv_lvl_e     priv_mode_i    [PMPNumChan],
   // Access checking channels
   input  logic [33:0]             pmp_req_addr_i [PMPNumChan],
@@ -37,6 +41,7 @@ module ibex_pmp #(
   logic [PMPNumChan-1:0][PMPNumRegions-1:0]   region_match_all;
   logic [PMPNumChan-1:0][PMPNumRegions-1:0]   region_basic_perm_check;
   logic [PMPNumChan-1:0][PMPNumRegions-1:0]   region_perm_check;
+  logic [PMPNumChan-1:0]                      debug_mode_allowed_access;
 
   ///////////////////////
   // Functions for PMP //
@@ -48,6 +53,7 @@ module ibex_pmp #(
   //                                                                                 |
   // region_match_all --------------------------------> access_fault_check <----------
   //                                                            |
+  // !debug_mode_allowed_access ------------------------------> &
   //                                                            \--> pmp_req_err_o
 
   // Compute permissions checks that apply when MSECCFG.MML is set. Added for Smepmp support.
@@ -226,14 +232,23 @@ module ibex_pmp #(
                              pmp_req_addr_i[c][PMPGranularity+2-1:0]};
     end
 
+    // Determine whether the core is in debug mode and the access is to an address in the range of
+    // the Debug Module.  According to Section A.2 of the RISC-V Debug Specification, the PMP must
+    // not disallow fetches, loads, or stores in the address range associated with the Debug Module
+    // when the hart is in debug mode.
+    assign debug_mode_allowed_access[c] = debug_mode_i &
+                                         ((pmp_req_addr_i[c] & ~DmAddrMask) == DmBaseAddr);
+
     // Once the permission checks of the regions are done, decide if the access is
     // denied by figuring out the matching region and its permission check.
     assign pmp_req_err_o[c] = access_fault_check(csr_pmp_mseccfg_i.mmwp,
                                                  csr_pmp_mseccfg_i.mml,
                                                  pmp_req_type_i[c],
                                                  region_match_all[c],
                                                  priv_mode_i[c],
-                                                 region_perm_check[c]);
+                                                 region_perm_check[c]) &
+                              // No error if the access is allowed as Debug Module access.
+                              ~debug_mode_allowed_access[c];
 
     // Access fails check against one region but access allowed due to another higher-priority
     // region.
diff --git a/rtl/ibex_top.sv b/rtl/ibex_top.sv
@@ -37,6 +37,8 @@ module ibex_top import ibex_pkg::*; #(
   parameter int unsigned            ICacheScrNumPrinceRoundsHalf = 2,
   parameter lfsr_seed_t             RndCnstLfsrSeed              = RndCnstLfsrSeedDefault,
   parameter lfsr_perm_t             RndCnstLfsrPerm              = RndCnstLfsrPermDefault,
+  parameter int unsigned            DmBaseAddr                   = 32'h1A110000,
+  parameter int unsigned            DmAddrMask                   = 32'h00000FFF,
   parameter int unsigned            DmHaltAddr                   = 32'h1A110800,
   parameter int unsigned            DmExceptionAddr              = 32'h1A110808,
   // Default seed and nonce for scrambling
@@ -313,6 +315,8 @@ module ibex_top import ibex_pkg::*; #(
     .RegFileDataWidth (RegFileDataWidth),
     .MemECC           (MemECC),
     .MemDataWidth     (MemDataWidth),
+    .DmBaseAddr       (DmBaseAddr),
+    .DmAddrMask       (DmAddrMask),
     .DmHaltAddr       (DmHaltAddr),
     .DmExceptionAddr  (DmExceptionAddr)
   ) u_ibex_core (
@@ -1120,6 +1124,10 @@ module ibex_top import ibex_pkg::*; #(
   assign alert_major_bus_o      = core_alert_major_bus | lockstep_alert_major_bus;
   assign alert_minor_o          = core_alert_minor | lockstep_alert_minor;
 
+  // Parameter assertions
+  `ASSERT_INIT(DmHaltAddrInRange_A, (DmHaltAddr & ~DmAddrMask) == DmBaseAddr)
+  `ASSERT_INIT(DmExceptionAddrInRange_A, (DmExceptionAddr & ~DmAddrMask) == DmBaseAddr)
+
   // X checks for top-level outputs
   `ASSERT_KNOWN(IbexInstrReqX, instr_req_o)
   `ASSERT_KNOWN_IF(IbexInstrReqPayloadX, instr_addr_o, instr_req_o)
diff --git a/rtl/ibex_top_tracing.sv b/rtl/ibex_top_tracing.sv
@@ -27,6 +27,8 @@ module ibex_top_tracing import ibex_pkg::*; #(
   parameter bit          ICacheScramble   = 1'b0,
   parameter lfsr_seed_t  RndCnstLfsrSeed  = RndCnstLfsrSeedDefault,
   parameter lfsr_perm_t  RndCnstLfsrPerm  = RndCnstLfsrPermDefault,
+  parameter int unsigned DmBaseAddr       = 32'h1A110000,
+  parameter int unsigned DmAddrMask       = 32'h00000FFF,
   parameter int unsigned DmHaltAddr       = 32'h1A110800,
   parameter int unsigned DmExceptionAddr  = 32'h1A110808
 ) (
@@ -184,6 +186,8 @@ module ibex_top_tracing import ibex_pkg::*; #(
     .ICacheScramble   ( ICacheScramble   ),
     .RndCnstLfsrSeed  ( RndCnstLfsrSeed  ),
     .RndCnstLfsrPerm  ( RndCnstLfsrPerm  ),
+    .DmBaseAddr       ( DmBaseAddr       ),
+    .DmAddrMask       ( DmAddrMask       ),
     .DmHaltAddr       ( DmHaltAddr       ),
     .DmExceptionAddr  ( DmExceptionAddr  )
   ) u_ibex_top (
