From b039c9611331ccf61a53b2d26d80a8cfb596e0ce Mon Sep 17 00:00:00 2001 From: Deepak Gupta Date: Tue, 8 Oct 2024 15:49:56 -0700 Subject: [PATCH] target/riscv: tracking indirect branches (fcfi) for zicfilp zicfilp protects forward control flow (if enabled) by enforcing all indirect call and jmp must land on a landing pad instruction `lpad`. If target of an indirect call or jmp is not `lpad` then cpu/hart must raise a sw check exception with tval = 2. This patch implements the mechanism using TCG. Target architecture branch instruction must define the end of a TB. Using this property, during translation of branch instruction, TB flag = FCFI_LP_EXPECTED can be set. Translation of target TB can check if FCFI_LP_EXPECTED flag is set and a flag (fcfi_lp_expected) can be set in DisasContext. If `lpad` gets translated, fcfi_lp_expected flag in DisasContext can be cleared. Else it'll fault. Signed-off-by: Deepak Gupta Co-developed-by: Jim Shu Co-developed-by: Andy Chiu Suggested-by: Richard Henderson Reviewed-by: Richard Henderson Reviewed-by: Alistair Francis Message-ID: <20241008225010.1861630-7-debug@rivosinc.com> Signed-off-by: Alistair Francis --- target/riscv/cpu.h | 3 +++ target/riscv/cpu_bits.h | 3 +++ target/riscv/cpu_helper.c | 10 ++++++++++ target/riscv/translate.c | 23 +++++++++++++++++++++++ 4 files changed, 39 insertions(+) diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h index 67ce6e0a03..c3a03f878b 100644 --- a/target/riscv/cpu.h +++ b/target/riscv/cpu.h @@ -622,6 +622,9 @@ FIELD(TB_FLAGS, ITRIGGER, 22, 1) FIELD(TB_FLAGS, VIRT_ENABLED, 23, 1) FIELD(TB_FLAGS, PRIV, 24, 2) FIELD(TB_FLAGS, AXL, 26, 2) +/* zicfilp needs a TB flag to track indirect branches */ +FIELD(TB_FLAGS, FCFI_ENABLED, 28, 1) +FIELD(TB_FLAGS, FCFI_LP_EXPECTED, 29, 1) #ifdef TARGET_RISCV32 #define riscv_cpu_mxl(env) ((void)(env), MXL_RV32) diff --git a/target/riscv/cpu_bits.h b/target/riscv/cpu_bits.h index 8df6043ef1..e7387c9b8f 100644 --- a/target/riscv/cpu_bits.h +++ b/target/riscv/cpu_bits.h @@ -692,6 +692,9 @@ typedef enum RISCVException { RISCV_EXCP_SEMIHOST = 0x3f, } RISCVException; +/* zicfilp defines lp violation results in sw check with tval = 2*/ +#define RISCV_EXCP_SW_CHECK_FCFI_TVAL 2 + #define RISCV_EXCP_INT_FLAG 0x80000000 #define RISCV_EXCP_INT_MASK 0x7fffffff diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c index fa4982e940..6a63c37083 100644 --- a/target/riscv/cpu_helper.c +++ b/target/riscv/cpu_helper.c @@ -132,6 +132,16 @@ void cpu_get_tb_cpu_state(CPURISCVState *env, vaddr *pc, flags = FIELD_DP32(flags, TB_FLAGS, VILL, 1); } + if (cpu_get_fcfien(env)) { + /* + * For Forward CFI, only the expectation of a lpad at + * the start of the block is tracked via env->elp. env->elp + * is turned on during jalr translation. + */ + flags = FIELD_DP32(flags, TB_FLAGS, FCFI_LP_EXPECTED, env->elp); + flags = FIELD_DP32(flags, TB_FLAGS, FCFI_ENABLED, 1); + } + #ifdef CONFIG_USER_ONLY fs = EXT_STATUS_DIRTY; vs = EXT_STATUS_DIRTY; diff --git a/target/riscv/translate.c b/target/riscv/translate.c index acba90f170..b5c0511b4b 100644 --- a/target/riscv/translate.c +++ b/target/riscv/translate.c @@ -116,6 +116,9 @@ typedef struct DisasContext { bool frm_valid; bool insn_start_updated; const GPtrArray *decoders; + /* zicfilp extension. fcfi_enabled, lp expected or not */ + bool fcfi_enabled; + bool fcfi_lp_expected; } DisasContext; static inline bool has_ext(DisasContext *ctx, uint32_t ext) @@ -1238,6 +1241,8 @@ static void riscv_tr_init_disas_context(DisasContextBase *dcbase, CPUState *cs) ctx->pm_base_enabled = FIELD_EX32(tb_flags, TB_FLAGS, PM_BASE_ENABLED); ctx->ztso = cpu->cfg.ext_ztso; ctx->itrigger = FIELD_EX32(tb_flags, TB_FLAGS, ITRIGGER); + ctx->fcfi_lp_expected = FIELD_EX32(tb_flags, TB_FLAGS, FCFI_LP_EXPECTED); + ctx->fcfi_enabled = FIELD_EX32(tb_flags, TB_FLAGS, FCFI_ENABLED); ctx->zero = tcg_constant_tl(0); ctx->virt_inst_excp = false; ctx->decoders = cpu->decoders; @@ -1270,6 +1275,24 @@ static void riscv_tr_translate_insn(DisasContextBase *dcbase, CPUState *cpu) decode_opc(env, ctx, opcode16); ctx->base.pc_next += ctx->cur_insn_len; + /* + * If 'fcfi_lp_expected' is still true after processing the instruction, + * then we did not see an 'lpad' instruction, and must raise an exception. + * Insert code to raise the exception at the start of the insn; any other + * code the insn may have emitted will be deleted as dead code following + * the noreturn exception + */ + if (ctx->fcfi_lp_expected) { + /* Emit after insn_start, i.e. before the op following insn_start. */ + tcg_ctx->emit_before_op = QTAILQ_NEXT(ctx->base.insn_start, link); + tcg_gen_st_tl(tcg_constant_tl(RISCV_EXCP_SW_CHECK_FCFI_TVAL), + tcg_env, offsetof(CPURISCVState, sw_check_code)); + gen_helper_raise_exception(tcg_env, + tcg_constant_i32(RISCV_EXCP_SW_CHECK)); + tcg_ctx->emit_before_op = NULL; + ctx->base.is_jmp = DISAS_NORETURN; + } + /* Only the first insn within a TB is allowed to cross a page boundary. */ if (ctx->base.is_jmp == DISAS_NEXT) { if (ctx->itrigger || !is_same_page(&ctx->base, ctx->base.pc_next)) {