zicfiss introduces a new state ssp ("shadow stack register") in cpu. ssp is expressed as a new unprivileged csr (CSR_SSP=0x11) and holds virtual address for shadow stack as programmed by software.
Shadow stack (for each mode) is enabled via bit3 in *envcfg CSRs. Shadow stack can be enabled for a mode only if it's higher privileged mode had it enabled for itself. M mode doesn't need enabling control, it's always available if extension is available on cpu. Signed-off-by: Deepak Gupta <de...@rivosinc.com> Co-developed-by: Jim Shu <jim....@sifive.com> Co-developed-by: Andy Chiu <andy.c...@sifive.com> --- target/riscv/cpu.c | 3 ++ target/riscv/cpu.h | 2 ++ target/riscv/cpu_bits.h | 6 ++++ target/riscv/csr.c | 74 +++++++++++++++++++++++++++++++++++++++++ 4 files changed, 85 insertions(+) diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c index 54fcf380ff..6b50ae0e45 100644 --- a/target/riscv/cpu.c +++ b/target/riscv/cpu.c @@ -998,6 +998,9 @@ static void riscv_cpu_reset_hold(Object *obj, ResetType type) /* on reset elp is set to NO_LP_EXPECTED */ env->elp = NO_LP_EXPECTED; + /* on reset ssp is set to 0 */ + env->ssp = 0; + /* * Bits 10, 6, 2 and 12 of mideleg are read only 1 when the Hypervisor * extension is enabled. diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h index 7fed5d2750..81283a1d76 100644 --- a/target/riscv/cpu.h +++ b/target/riscv/cpu.h @@ -224,6 +224,8 @@ struct CPUArchState { /* elp state for zicfilp extension */ cfi_elp elp; + /* shadow stack register for zicfiss extension */ + target_ulong ssp; /* sw check code for sw check exception */ target_ulong sw_check_code; #ifdef CONFIG_USER_ONLY diff --git a/target/riscv/cpu_bits.h b/target/riscv/cpu_bits.h index 477e24feaf..589326e516 100644 --- a/target/riscv/cpu_bits.h +++ b/target/riscv/cpu_bits.h @@ -34,6 +34,9 @@ /* Control and Status Registers */ +/* zicfiss user ssp csr */ +#define CSR_SSP 0x011 + /* User Trap Setup */ #define CSR_USTATUS 0x000 #define CSR_UIE 0x004 @@ -760,6 +763,7 @@ typedef enum RISCVException { /* Execution environment configuration bits */ #define MENVCFG_FIOM BIT(0) #define MENVCFG_LPE BIT(2) /* zicfilp */ +#define MENVCFG_SSE BIT(3) /* zicfiss */ #define MENVCFG_CBIE (3UL << 4) #define MENVCFG_CBCFE BIT(6) #define MENVCFG_CBZE BIT(7) @@ -774,12 +778,14 @@ typedef enum RISCVException { #define SENVCFG_FIOM MENVCFG_FIOM #define SENVCFG_LPE MENVCFG_LPE +#define SENVCFG_SSE MENVCFG_SSE #define SENVCFG_CBIE MENVCFG_CBIE #define SENVCFG_CBCFE MENVCFG_CBCFE #define SENVCFG_CBZE MENVCFG_CBZE #define HENVCFG_FIOM MENVCFG_FIOM #define HENVCFG_LPE MENVCFG_LPE +#define HENVCFG_SSE MENVCFG_SSE #define HENVCFG_CBIE MENVCFG_CBIE #define HENVCFG_CBCFE MENVCFG_CBCFE #define HENVCFG_CBZE MENVCFG_CBZE diff --git a/target/riscv/csr.c b/target/riscv/csr.c index a5a969a377..d72d6289fb 100644 --- a/target/riscv/csr.c +++ b/target/riscv/csr.c @@ -185,6 +185,47 @@ static RISCVException zcmt(CPURISCVState *env, int csrno) return RISCV_EXCP_NONE; } +static RISCVException cfi_ss(CPURISCVState *env, int csrno) +{ + /* no cfi extension, access to csr is illegal */ + if (!env_archcpu(env)->cfg.ext_zicfiss) { + return RISCV_EXCP_ILLEGAL_INST; + } + /* + * CONFIG_USER_MODE always allow access for now. Better for user mode only + * functionality + */ +#if !defined(CONFIG_USER_ONLY) + if (env->debugger) { + return RISCV_EXCP_NONE; + } + /* current priv not M */ + if (env->priv != PRV_M) { + /* menvcfg says no shadow stack enable */ + if (!get_field(env->menvcfg, MENVCFG_SSE)) { + return RISCV_EXCP_ILLEGAL_INST; + } + + /* V = 1 and henvcfg says no shadow stack enable */ + if (env->virt_enabled && + !get_field(env->henvcfg, HENVCFG_SSE)) { + return RISCV_EXCP_VIRT_INSTRUCTION_FAULT; + } + + /* + * SSP are not accessible to U mode if disabled via senvcfg + * CSR + */ + if ((env->priv == PRV_U) && + (!get_field(env->senvcfg, SENVCFG_SSE))) { + return RISCV_EXCP_ILLEGAL_INST; + } + } +#endif + + return RISCV_EXCP_NONE; +} + #if !defined(CONFIG_USER_ONLY) static RISCVException mctr(CPURISCVState *env, int csrno) { @@ -596,6 +637,19 @@ static RISCVException seed(CPURISCVState *env, int csrno) #endif } +/* zicfiss CSR_SSP read and write */ +static int read_ssp(CPURISCVState *env, int csrno, target_ulong *val) +{ + *val = env->ssp; + return RISCV_EXCP_NONE; +} + +static int write_ssp(CPURISCVState *env, int csrno, target_ulong val) +{ + env->ssp = val; + return RISCV_EXCP_NONE; +} + /* User Floating-Point CSRs */ static RISCVException read_fflags(CPURISCVState *env, int csrno, target_ulong *val) @@ -2111,6 +2165,10 @@ static RISCVException write_menvcfg(CPURISCVState *env, int csrno, if (env_archcpu(env)->cfg.ext_zicfilp) { mask |= MENVCFG_LPE; } + + if (env_archcpu(env)->cfg.ext_zicfiss) { + mask |= MENVCFG_SSE; + } } env->menvcfg = (env->menvcfg & ~mask) | (val & mask); @@ -2167,6 +2225,13 @@ static RISCVException write_senvcfg(CPURISCVState *env, int csrno, mask |= SENVCFG_LPE; } + /* Higher mode SSE must be ON for next-less mode SSE to be ON */ + if (env_archcpu(env)->cfg.ext_zicfiss && + get_field(env->menvcfg, MENVCFG_SSE) && + (env->virt_enabled ? get_field(env->henvcfg, HENVCFG_SSE) : true)) { + mask |= SENVCFG_SSE; + } + env->senvcfg = (env->senvcfg & ~mask) | (val & mask); return RISCV_EXCP_NONE; } @@ -2208,6 +2273,12 @@ static RISCVException write_henvcfg(CPURISCVState *env, int csrno, if (env_archcpu(env)->cfg.ext_zicfilp) { mask |= HENVCFG_LPE; } + + /* H can light up SSE for VS only if HS had it from menvcfg */ + if (env_archcpu(env)->cfg.ext_zicfiss && + get_field(env->menvcfg, MENVCFG_SSE)) { + mask |= HENVCFG_SSE; + } } env->henvcfg = (env->henvcfg & ~mask) | (val & mask); @@ -4663,6 +4734,9 @@ riscv_csr_operations csr_ops[CSR_TABLE_SIZE] = { /* Zcmt Extension */ [CSR_JVT] = {"jvt", zcmt, read_jvt, write_jvt}, + /* zicfiss Extension, shadow stack register */ + [CSR_SSP] = { "ssp", cfi_ss, read_ssp, write_ssp }, + #if !defined(CONFIG_USER_ONLY) /* Machine Timers and Counters */ [CSR_MCYCLE] = { "mcycle", any, read_hpmcounter, -- 2.44.0