Messages in this thread Patch in this message | | | From | Deepak Gupta <> | Subject | [PATCH v1 RFC Zisslpcfi 13/20] riscv: illegal instruction handler for cfi violations | Date | Sun, 12 Feb 2023 20:53:42 -0800 |
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Zisslpcfi spec proposes that cfi violations are reported as illegal instruction exception. Following are the cases
- elp missing: An indirect jmp/call landed on instruction which is not `lpcll` - label mismatch: Static label embedded in instr `lpcll/lpcml/lpcul` doesn't match with repsective label in CSR_LPLR - sscheckra: x1 and x5 don't match.
Current changes run user code in audit mode. That means that any cfi violation is suppressed and app is allowed to continue.
Signed-off-by: Deepak Gupta <debug@rivosinc.com> --- arch/riscv/kernel/traps.c | 79 ++++++++++++++++++++++++++++++++++++++- 1 file changed, 77 insertions(+), 2 deletions(-)
diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c index 5553b8d48ba5..a292699f4f25 100644 --- a/arch/riscv/kernel/traps.c +++ b/arch/riscv/kernel/traps.c @@ -97,6 +97,10 @@ static void do_trap_error(struct pt_regs *regs, int signo, int code, /* Zisslpcfi instructions encodings */ #define SS_PUSH_POP 0x81C04073 #define SS_AMOSWAP 0x82004073 +#define SS_CHECKRA 0x8A12C073 +#define LP_C_LL 0x83004073 +#define LP_C_ML 0x86804073 +#define LP_C_UL 0x8B804073 bool is_ss_load_store_insn(unsigned long insn) { @@ -112,6 +116,71 @@ bool is_ss_load_store_insn(unsigned long insn) return false; } +bool is_cfi_violation_insn(unsigned long insn) +{ + struct task_struct *task = current; + bool ss_exist = false, lp_exist = false; + + ss_exist = arch_supports_shadow_stack(); + lp_exist = arch_supports_indirect_br_lp_instr(); + + if (ss_exist && (insn == SS_CHECKRA)) { + pr_warn("cfi violation (sschkra): comm = %s, task = %p\n", task->comm, task); + return true; + } + if (lp_exist && ((insn & LP_C_LL) == LP_C_LL)) { + pr_warn("cfi violation (lpcll): comm = %s, task = %p\n", task->comm, task); + return true; + } + if (lp_exist && ((insn & LP_C_ML) == LP_C_ML)) { + pr_warn("cfi violation (lpcml): comm = %s, task = %p\n", task->comm, task); + return true; + } + if (lp_exist && ((insn & LP_C_UL) == LP_C_UL)) { + pr_warn("cfi violation (lpcul): comm = %s, task = %p\n", task->comm, task); + return true; + } + + return false; +} + +int handle_illegal_instruction(struct pt_regs *regs) +{ + /* stval should hold faulting opcode */ + unsigned long insn = csr_read(stval); + struct thread_info *info = NULL; + struct task_struct *task = current; + + info = current_thread_info(); + /* + * If CFI enabled then following instructions leads to illegal instruction fault + * -- sscheckra: x1 and x5 mismatch + * -- ELP = 1, Any instruction other than lpcll will fault + * -- lpcll will fault if lower label don't match with LPLR.LL + * -- lpcml will fault if lower label don't match with LPLR.ML + * -- lpcul will fault if lower label don't match with LPLR.UL + */ + + /* If fcfi enabled and ELP = 1, suppress ELP (audit mode) and resume */ + if (arch_supports_indirect_br_lp_instr() && +#ifdef CONFIG_USER_INDIRECT_BR_LP + info->user_cfi_state.ufcfi_en && +#endif + (regs->status & SR_ELP)) { + pr_warn("cfi violation (elp): comm = %s, task = %p\n", task->comm, task); + regs->status &= ~(SR_ELP); + return 0; + } + /* if faulting opcode is sscheckra/lpcll/lpcml/lpcll, advance PC and resume */ + if (is_cfi_violation_insn(insn)) { + /* no compressed form for zisslpcfi instructions */ + regs->epc += 4; + return 0; + } + + return 1; +} + ulong get_instruction(ulong epc) { ulong *epc_ptr = (ulong *) epc; @@ -190,8 +259,14 @@ DO_ERROR_INFO(do_trap_insn_misaligned, SIGBUS, BUS_ADRALN, "instruction address misaligned"); DO_ERROR_INFO(do_trap_insn_fault, SIGSEGV, SEGV_ACCERR, "instruction access fault"); -DO_ERROR_INFO(do_trap_insn_illegal, - SIGILL, ILL_ILLOPC, "illegal instruction"); + +asmlinkage void __trap_section do_trap_insn_illegal(struct pt_regs *regs) +{ + if (!handle_illegal_instruction(regs)) + return; + do_trap_error(regs, SIGILL, ILL_ILLOPC, regs->epc, + "illegal instruction"); +} #ifdef CONFIG_USER_SHADOW_STACK asmlinkage void __trap_section do_trap_load_fault(struct pt_regs *regs) { -- 2.25.1
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