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Date: Fri, 13 May 2022 13:21:58 -0700 From: Sami Tolvanen <samitolvanen@...gle.com> To: linux-kernel@...r.kernel.org Cc: Kees Cook <keescook@...omium.org>, Josh Poimboeuf <jpoimboe@...hat.com>, Peter Zijlstra <peterz@...radead.org>, x86@...nel.org, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>, Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, Joao Moreira <joao@...rdrivepizza.com>, Sedat Dilek <sedat.dilek@...il.com>, Steven Rostedt <rostedt@...dmis.org>, linux-hardening@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, llvm@...ts.linux.dev, Sami Tolvanen <samitolvanen@...gle.com> Subject: [RFC PATCH v2 20/21] x86: Add support for CONFIG_CFI_CLANG 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 __cfi_function: int3 int3 mov <id>, %eax int3 int3 function: ... ; indirect call check cmpl <id>, -6(%r11) je .Ltmp1 ud2 .Ltmp1: call __x86_indirect_thunk_r11 Define the __CFI_TYPE helper macro for manual type annotations in assembly code, add error handling for the CFI ud2 traps, and allow CONFIG_CFI_CLANG to be selected on x86_64. Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com> --- arch/x86/Kconfig | 2 ++ arch/x86/include/asm/linkage.h | 12 +++++++ arch/x86/kernel/traps.c | 60 +++++++++++++++++++++++++++++++++- 3 files changed, 73 insertions(+), 1 deletion(-) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 4bed3abf444d..2e73d0792d48 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -108,6 +108,8 @@ config X86 select ARCH_SUPPORTS_PAGE_TABLE_CHECK if X86_64 select ARCH_SUPPORTS_NUMA_BALANCING if X86_64 select ARCH_SUPPORTS_KMAP_LOCAL_FORCE_MAP if NR_CPUS <= 4096 + select ARCH_SUPPORTS_CFI_CLANG if X86_64 + select ARCH_USES_CFI_TRAPS if X86_64 && CFI_CLANG select ARCH_SUPPORTS_LTO_CLANG select ARCH_SUPPORTS_LTO_CLANG_THIN select ARCH_USE_BUILTIN_BSWAP diff --git a/arch/x86/include/asm/linkage.h b/arch/x86/include/asm/linkage.h index 85865f1645bd..0ee4a0af3974 100644 --- a/arch/x86/include/asm/linkage.h +++ b/arch/x86/include/asm/linkage.h @@ -25,6 +25,18 @@ #define RET ret #endif +#ifdef CONFIG_CFI_CLANG +#define __CFI_TYPE(name) \ + .fill 7, 1, 0xCC ASM_NL \ + SYM_START(__cfi_##name, SYM_L_LOCAL, SYM_A_NONE) \ + int3 ASM_NL \ + int3 ASM_NL \ + mov __kcfi_typeid_##name, %eax ASM_NL \ + int3 ASM_NL \ + int3 ASM_NL \ + SYM_FUNC_END(__cfi_##name) +#endif + #else /* __ASSEMBLY__ */ #ifdef CONFIG_SLS diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c index 1563fb995005..320e257eb4be 100644 --- a/arch/x86/kernel/traps.c +++ b/arch/x86/kernel/traps.c @@ -40,6 +40,7 @@ #include <linux/hardirq.h> #include <linux/atomic.h> #include <linux/ioasid.h> +#include <linux/cfi.h> #include <asm/stacktrace.h> #include <asm/processor.h> @@ -295,6 +296,62 @@ static inline void handle_invalid_op(struct pt_regs *regs) ILL_ILLOPN, error_get_trap_addr(regs)); } +#ifdef CONFIG_CFI_CLANG +static void decode_cfi_insn(struct pt_regs *regs, unsigned long *target, + unsigned long *type) +{ + char buffer[MAX_INSN_SIZE]; + struct insn insn; + int offset; + + *target = *type = 0; + + /* + * The compiler generates the following instruction sequence + * for indirect call checks: + * + * cmpl <id>, -6(%reg) ; 7 bytes + * je .Ltmp1 ; 2 bytes + * ud2 ; <- addr + * .Ltmp1: + * + * Both the type and the target address can be decoded from the + * cmpl instruction. + */ + if (copy_from_kernel_nofault(buffer, (void *)regs->ip - 9, MAX_INSN_SIZE)) + return; + if (insn_decode_kernel(&insn, buffer)) + return; + if (insn.opcode.value != 0x81 || X86_MODRM_REG(insn.modrm.value) != 7) + return; + + *type = insn.immediate.value; + + offset = insn_get_modrm_rm_off(&insn, regs); + if (offset < 0) + return; + + *target = *(unsigned long *)((void *)regs + offset); +} + +static enum bug_trap_type handle_cfi_failure(struct pt_regs *regs) +{ + if (is_cfi_trap(regs->ip)) { + unsigned long target, type; + + decode_cfi_insn(regs, &target, &type); + return report_cfi_failure(regs, regs->ip, target, type); + } + + return BUG_TRAP_TYPE_NONE; +} +#else +static inline enum bug_trap_type handle_cfi_failure(struct pt_regs *regs) +{ + return BUG_TRAP_TYPE_NONE; +} +#endif /* CONFIG_CFI_CLANG */ + static noinstr bool handle_bug(struct pt_regs *regs) { bool handled = false; @@ -312,7 +369,8 @@ static noinstr bool handle_bug(struct pt_regs *regs) */ if (regs->flags & X86_EFLAGS_IF) raw_local_irq_enable(); - if (report_bug(regs->ip, regs) == BUG_TRAP_TYPE_WARN) { + if (report_bug(regs->ip, regs) == BUG_TRAP_TYPE_WARN || + handle_cfi_failure(regs) == BUG_TRAP_TYPE_WARN) { regs->ip += LEN_UD2; handled = true; } -- 2.36.0.550.gb090851708-goog
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