From: Sami Tolvanen samitolvanen@google.com
[ Upstream commit af0ead42f69389cd4ed68e1a4c6cde45c0adb35c ]
With CONFIG_CFI_CLANG, the compiler injects a type preamble immediately before each function and a check to validate the target function type before indirect calls:
; type preamble .word <id> function: ... ; indirect call check lw t1, -4(a0) lui t2, <hi20> addiw t2, t2, <lo12> beq t1, t2, .Ltmp0 ebreak .Ltmp0: jarl a0
Implement error handling code for the ebreak traps emitted for the checks. This produces the following oops on a CFI failure (generated using lkdtm):
[ 21.177245] CFI failure at lkdtm_indirect_call+0x22/0x32 [lkdtm] (target: lkdtm_increment_int+0x0/0x18 [lkdtm]; expected type: 0x3ad55aca) [ 21.178483] Kernel BUG [#1] [ 21.178671] Modules linked in: lkdtm [ 21.179037] CPU: 1 PID: 104 Comm: sh Not tainted 6.3.0-rc6-00037-g37d5ec6297ab #1 [ 21.179511] Hardware name: riscv-virtio,qemu (DT) [ 21.179818] epc : lkdtm_indirect_call+0x22/0x32 [lkdtm] [ 21.180106] ra : lkdtm_CFI_FORWARD_PROTO+0x48/0x7c [lkdtm] [ 21.180426] epc : ffffffff01387092 ra : ffffffff01386f14 sp : ff20000000453cf0 [ 21.180792] gp : ffffffff81308c38 tp : ff6000000243f080 t0 : ff20000000453b78 [ 21.181157] t1 : 000000003ad55aca t2 : 000000007e0c52a5 s0 : ff20000000453d00 [ 21.181506] s1 : 0000000000000001 a0 : ffffffff0138d170 a1 : ffffffff013870bc [ 21.181819] a2 : b5fea48dd89aa700 a3 : 0000000000000001 a4 : 0000000000000fff [ 21.182169] a5 : 0000000000000004 a6 : 00000000000000b7 a7 : 0000000000000000 [ 21.182591] s2 : ff20000000453e78 s3 : ffffffffffffffea s4 : 0000000000000012 [ 21.183001] s5 : ff600000023c7000 s6 : 0000000000000006 s7 : ffffffff013882a0 [ 21.183653] s8 : 0000000000000008 s9 : 0000000000000002 s10: ffffffff0138d878 [ 21.184245] s11: ffffffff0138d878 t3 : 0000000000000003 t4 : 0000000000000000 [ 21.184591] t5 : ffffffff8133df08 t6 : ffffffff8133df07 [ 21.184858] status: 0000000000000120 badaddr: 0000000000000000 cause: 0000000000000003 [ 21.185415] [<ffffffff01387092>] lkdtm_indirect_call+0x22/0x32 [lkdtm] [ 21.185772] [<ffffffff01386f14>] lkdtm_CFI_FORWARD_PROTO+0x48/0x7c [lkdtm] [ 21.186093] [<ffffffff01383552>] lkdtm_do_action+0x22/0x34 [lkdtm] [ 21.186445] [<ffffffff0138350c>] direct_entry+0x128/0x13a [lkdtm] [ 21.186817] [<ffffffff8033ed8c>] full_proxy_write+0x58/0xb2 [ 21.187352] [<ffffffff801d4fe8>] vfs_write+0x14c/0x33a [ 21.187644] [<ffffffff801d5328>] ksys_write+0x64/0xd4 [ 21.187832] [<ffffffff801d53a6>] sys_write+0xe/0x1a [ 21.188171] [<ffffffff80003996>] ret_from_syscall+0x0/0x2 [ 21.188595] Code: 0513 0f65 a303 ffc5 53b7 7e0c 839b 2a53 0363 0073 (9002) 9582 [ 21.189178] ---[ end trace 0000000000000000 ]--- [ 21.189590] Kernel panic - not syncing: Fatal exception
Reviewed-by: Kees Cook keescook@chromium.org Reviewed-by: Conor Dooley conor.dooley@microchip.com # ISA bits Tested-by: Nathan Chancellor nathan@kernel.org Signed-off-by: Sami Tolvanen samitolvanen@google.com Link: https://lore.kernel.org/r/20230710183544.999540-12-samitolvanen@google.com Signed-off-by: Palmer Dabbelt palmer@rivosinc.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/riscv/Kconfig | 1 + arch/riscv/include/asm/cfi.h | 22 ++++++++++ arch/riscv/include/asm/insn.h | 10 +++++ arch/riscv/kernel/Makefile | 2 + arch/riscv/kernel/cfi.c | 77 +++++++++++++++++++++++++++++++++++ arch/riscv/kernel/traps.c | 4 +- 6 files changed, 115 insertions(+), 1 deletion(-) create mode 100644 arch/riscv/include/asm/cfi.h create mode 100644 arch/riscv/kernel/cfi.c
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index bea7b73e895dd..6f16e8a7ec75e 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -48,6 +48,7 @@ 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 0000000000000..56bf9d69d5e38 --- /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 <linux/cfi.h> + +#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 fce00400c9bcc..06e439eeef9ad 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 */ @@ -130,6 +131,7 @@ #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 @@ -289,6 +291,10 @@ static __always_inline bool riscv_insn_is_c_jalr(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)); }) @@ -316,6 +322,10 @@ static __always_inline bool riscv_insn_is_c_jalr(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 506cc4a9a45a5..6ac56af42f4a0 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 0000000000000..820158d7a2913 --- /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 <asm/cfi.h> +#include <asm/insn.h> + +/* + * 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(<reg>) + * lui t2, <hi20> + * addiw t2, t2, <lo12> + * beq t1, t2, .Ltmp1 + * ebreak ; <- regs->epc + * .Ltmp1: + * jalr <reg> + * + * 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 f798c853bede6..19807c4d3805d 100644 --- a/arch/riscv/kernel/traps.c +++ b/arch/riscv/kernel/traps.c @@ -21,6 +21,7 @@
#include <asm/asm-prototypes.h> #include <asm/bug.h> +#include <asm/cfi.h> #include <asm/csr.h> #include <asm/processor.h> #include <asm/ptrace.h> @@ -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");