diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index a475ef1a0c1c..29fdba9d8514 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -49,6 +49,7 @@ config RISCV select ARCH_SUPPORTS_PER_VMA_LOCK if MMU select ARCH_USE_MEMTEST select ARCH_USE_QUEUED_RWLOCKS + select ARCH_USES_CFI_TRAPS if CFI_CLANG select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU select ARCH_WANT_FRAME_POINTERS select ARCH_WANT_GENERAL_HUGETLB if !RISCV_ISA_SVNAPOT diff --git a/arch/riscv/include/asm/cfi.h b/arch/riscv/include/asm/cfi.h new file mode 100644 index 000000000000..56bf9d69d5e3 --- /dev/null +++ b/arch/riscv/include/asm/cfi.h @@ -0,0 +1,22 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _ASM_RISCV_CFI_H +#define _ASM_RISCV_CFI_H + +/* + * Clang Control Flow Integrity (CFI) support. + * + * Copyright (C) 2023 Google LLC + */ + +#include + +#ifdef CONFIG_CFI_CLANG +enum bug_trap_type handle_cfi_failure(struct pt_regs *regs); +#else +static inline enum bug_trap_type handle_cfi_failure(struct pt_regs *regs) +{ + return BUG_TRAP_TYPE_NONE; +} +#endif /* CONFIG_CFI_CLANG */ + +#endif /* _ASM_RISCV_CFI_H */ diff --git a/arch/riscv/include/asm/insn.h b/arch/riscv/include/asm/insn.h index 4e1505cef8aa..9c23f598434c 100644 --- a/arch/riscv/include/asm/insn.h +++ b/arch/riscv/include/asm/insn.h @@ -63,6 +63,7 @@ #define RVG_RS1_OPOFF 15 #define RVG_RS2_OPOFF 20 #define RVG_RD_OPOFF 7 +#define RVG_RS1_MASK GENMASK(4, 0) #define RVG_RD_MASK GENMASK(4, 0) /* The bit field of immediate value in RVC J instruction */ @@ -129,6 +130,7 @@ #define RVC_C2_RS1_OPOFF 7 #define RVC_C2_RS2_OPOFF 2 #define RVC_C2_RD_OPOFF 7 +#define RVC_C2_RS1_MASK GENMASK(4, 0) /* parts of opcode for RVG*/ #define RVG_OPCODE_FENCE 0x0f @@ -278,6 +280,10 @@ static __always_inline bool riscv_insn_is_branch(u32 code) #define RV_X(X, s, mask) (((X) >> (s)) & (mask)) #define RVC_X(X, s, mask) RV_X(X, s, mask) +#define RV_EXTRACT_RS1_REG(x) \ + ({typeof(x) x_ = (x); \ + (RV_X(x_, RVG_RS1_OPOFF, RVG_RS1_MASK)); }) + #define RV_EXTRACT_RD_REG(x) \ ({typeof(x) x_ = (x); \ (RV_X(x_, RVG_RD_OPOFF, RVG_RD_MASK)); }) @@ -305,6 +311,10 @@ static __always_inline bool riscv_insn_is_branch(u32 code) (RV_X(x_, RV_B_IMM_11_OPOFF, RV_B_IMM_11_MASK) << RV_B_IMM_11_OFF) | \ (RV_IMM_SIGN(x_) << RV_B_IMM_SIGN_OFF); }) +#define RVC_EXTRACT_C2_RS1_REG(x) \ + ({typeof(x) x_ = (x); \ + (RV_X(x_, RVC_C2_RS1_OPOFF, RVC_C2_RS1_MASK)); }) + #define RVC_EXTRACT_JTYPE_IMM(x) \ ({typeof(x) x_ = (x); \ (RVC_X(x_, RVC_J_IMM_3_1_OPOFF, RVC_J_IMM_3_1_MASK) << RVC_J_IMM_3_1_OFF) | \ diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile index 506cc4a9a45a..6ac56af42f4a 100644 --- a/arch/riscv/kernel/Makefile +++ b/arch/riscv/kernel/Makefile @@ -91,6 +91,8 @@ obj-$(CONFIG_CRASH_CORE) += crash_core.o obj-$(CONFIG_JUMP_LABEL) += jump_label.o +obj-$(CONFIG_CFI_CLANG) += cfi.o + obj-$(CONFIG_EFI) += efi.o obj-$(CONFIG_COMPAT) += compat_syscall_table.o obj-$(CONFIG_COMPAT) += compat_signal.o diff --git a/arch/riscv/kernel/cfi.c b/arch/riscv/kernel/cfi.c new file mode 100644 index 000000000000..820158d7a291 --- /dev/null +++ b/arch/riscv/kernel/cfi.c @@ -0,0 +1,77 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Clang Control Flow Integrity (CFI) support. + * + * Copyright (C) 2023 Google LLC + */ +#include +#include + +/* + * Returns the target address and the expected type when regs->epc points + * to a compiler-generated CFI trap. + */ +static bool decode_cfi_insn(struct pt_regs *regs, unsigned long *target, + u32 *type) +{ + unsigned long *regs_ptr = (unsigned long *)regs; + int rs1_num; + u32 insn; + + *target = *type = 0; + + /* + * The compiler generates the following instruction sequence + * for indirect call checks: + * + *   lw t1, -4() + * lui t2, + * addiw t2, t2, + * beq t1, t2, .Ltmp1 + * ebreak ; <- regs->epc + * .Ltmp1: + * jalr + * + * We can read the expected type and the target address from the + * registers passed to the beq/jalr instructions. + */ + if (get_kernel_nofault(insn, (void *)regs->epc - 4)) + return false; + if (!riscv_insn_is_beq(insn)) + return false; + + *type = (u32)regs_ptr[RV_EXTRACT_RS1_REG(insn)]; + + if (get_kernel_nofault(insn, (void *)regs->epc) || + get_kernel_nofault(insn, (void *)regs->epc + GET_INSN_LENGTH(insn))) + return false; + + if (riscv_insn_is_jalr(insn)) + rs1_num = RV_EXTRACT_RS1_REG(insn); + else if (riscv_insn_is_c_jalr(insn)) + rs1_num = RVC_EXTRACT_C2_RS1_REG(insn); + else + return false; + + *target = regs_ptr[rs1_num]; + + return true; +} + +/* + * Checks if the ebreak trap is because of a CFI failure, and handles the trap + * if needed. Returns a bug_trap_type value similarly to report_bug. + */ +enum bug_trap_type handle_cfi_failure(struct pt_regs *regs) +{ + unsigned long target; + u32 type; + + if (!is_cfi_trap(regs->epc)) + return BUG_TRAP_TYPE_NONE; + + if (!decode_cfi_insn(regs, &target, &type)) + return report_cfi_failure_noaddr(regs, regs->epc); + + return report_cfi_failure(regs, regs->epc, &target, type); +} diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c index f910dfccbf5d..212dc20631fb 100644 --- a/arch/riscv/kernel/traps.c +++ b/arch/riscv/kernel/traps.c @@ -21,6 +21,7 @@ #include #include +#include #include #include #include @@ -271,7 +272,8 @@ void handle_break(struct pt_regs *regs) == NOTIFY_STOP) return; #endif - else if (report_bug(regs->epc, regs) == BUG_TRAP_TYPE_WARN) + else if (report_bug(regs->epc, regs) == BUG_TRAP_TYPE_WARN || + handle_cfi_failure(regs) == BUG_TRAP_TYPE_WARN) regs->epc += get_break_insn_length(regs->epc); else die(regs, "Kernel BUG");