From: Linus Walleij <linus.walleij@linaro.org> To: Russell King <linux@armlinux.org.uk>, Sami Tolvanen <samitolvanen@google.com>, Kees Cook <keescook@chromium.org>, Nathan Chancellor <nathan@kernel.org>, Nick Desaulniers <ndesaulniers@google.com>, Ard Biesheuvel <ardb@kernel.org>, Arnd Bergmann <arnd@arndb.de> Cc: linux-arm-kernel@lists.infradead.org, llvm@lists.linux.dev, Linus Walleij <linus.walleij@linaro.org> Subject: [PATCH v4 7/8] ARM: hw_breakpoint: Handle CFI breakpoints Date: Thu, 28 Mar 2024 09:19:30 +0100 [thread overview] Message-ID: <20240328-arm32-cfi-v4-7-a11046139125@linaro.org> (raw) In-Reply-To: <20240328-arm32-cfi-v4-0-a11046139125@linaro.org> This registers a breakpoint handler for the new breakpoint type (0x03) inserted by LLVM CLANG for CFI breakpoints. If we are in permissive mode, just print a backtrace and continue. Example with CONFIG_CFI_PERMISSIVE enabled: > echo CFI_FORWARD_PROTO > /sys/kernel/debug/provoke-crash/DIRECT lkdtm: Performing direct entry CFI_FORWARD_PROTO lkdtm: Calling matched prototype ... lkdtm: Calling mismatched prototype ... CFI failure at lkdtm_indirect_call+0x40/0x4c (target: 0x0; expected type: 0x00000000) WARNING: CPU: 1 PID: 112 at lkdtm_indirect_call+0x40/0x4c CPU: 1 PID: 112 Comm: sh Not tainted 6.8.0-rc1+ #150 Hardware name: ARM-Versatile Express (...) lkdtm: FAIL: survived mismatched prototype function call! lkdtm: Unexpected! This kernel (6.8.0-rc1+ armv7l) was built with CONFIG_CFI_CLANG=y As you can see the LKDTM test fails, but I expect that this would be expected behaviour in the permissive mode. We are currently not implementing target and type for the CFI breakpoint as this requires additional operand bundling compiler extensions. CPUs without breakpoint support cannot handle breakpoints naturally, in these cases the permissive mode will not work, CFI will fall over on an undefined instruction: Internal error: Oops - undefined instruction: 0 [#1] PREEMPT ARM CPU: 0 PID: 186 Comm: ash Tainted: G W 6.9.0-rc1+ #7 Hardware name: Gemini (Device Tree) PC is at lkdtm_indirect_call+0x38/0x4c LR is at lkdtm_CFI_FORWARD_PROTO+0x30/0x6c This is reasonable I think: it's the best CFI can do to ascertain the the control flow is not broken on these CPUs. Signed-off-by: Linus Walleij <linus.walleij@linaro.org> --- arch/arm/include/asm/hw_breakpoint.h | 1 + arch/arm/kernel/hw_breakpoint.c | 30 ++++++++++++++++++++++++++++++ 2 files changed, 31 insertions(+) diff --git a/arch/arm/include/asm/hw_breakpoint.h b/arch/arm/include/asm/hw_breakpoint.h index 62358d3ca0a8..e7f9961c53b2 100644 --- a/arch/arm/include/asm/hw_breakpoint.h +++ b/arch/arm/include/asm/hw_breakpoint.h @@ -84,6 +84,7 @@ static inline void decode_ctrl_reg(u32 reg, #define ARM_DSCR_MOE(x) ((x >> 2) & 0xf) #define ARM_ENTRY_BREAKPOINT 0x1 #define ARM_ENTRY_ASYNC_WATCHPOINT 0x2 +#define ARM_ENTRY_CFI_BREAKPOINT 0x3 #define ARM_ENTRY_SYNC_WATCHPOINT 0xa /* DSCR monitor/halting bits. */ diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c index dc0fb7a81371..ce7c152dd6e9 100644 --- a/arch/arm/kernel/hw_breakpoint.c +++ b/arch/arm/kernel/hw_breakpoint.c @@ -17,6 +17,7 @@ #include <linux/perf_event.h> #include <linux/hw_breakpoint.h> #include <linux/smp.h> +#include <linux/cfi.h> #include <linux/cpu_pm.h> #include <linux/coresight.h> @@ -903,6 +904,32 @@ static void breakpoint_handler(unsigned long unknown, struct pt_regs *regs) watchpoint_single_step_handler(addr); } +#ifdef CONFIG_CFI_CLANG +static void hw_breakpoint_cfi_handler(struct pt_regs *regs) +{ + /* TODO: implementing target and type requires compiler work */ + unsigned long target = 0; + u32 type = 0; + + switch (report_cfi_failure(regs, instruction_pointer(regs), &target, type)) { + case BUG_TRAP_TYPE_BUG: + die("Oops - CFI", regs, 0); + break; + case BUG_TRAP_TYPE_WARN: + /* Skip the breaking instruction */ + instruction_pointer(regs) += 4; + break; + default: + die("Unknown CFI error", regs, 0); + break; + } +} +#else +static void hw_breakpoint_cfi_handler(struct pt_regs *regs) +{ +} +#endif + /* * Called from either the Data Abort Handler [watchpoint] or the * Prefetch Abort Handler [breakpoint] with interrupts disabled. @@ -932,6 +959,9 @@ static int hw_breakpoint_pending(unsigned long addr, unsigned int fsr, case ARM_ENTRY_SYNC_WATCHPOINT: watchpoint_handler(addr, fsr, regs); break; + case ARM_ENTRY_CFI_BREAKPOINT: + hw_breakpoint_cfi_handler(regs); + break; default: ret = 1; /* Unhandled fault. */ } -- 2.44.0
WARNING: multiple messages have this Message-ID (diff)
From: Linus Walleij <linus.walleij@linaro.org> To: Russell King <linux@armlinux.org.uk>, Sami Tolvanen <samitolvanen@google.com>, Kees Cook <keescook@chromium.org>, Nathan Chancellor <nathan@kernel.org>, Nick Desaulniers <ndesaulniers@google.com>, Ard Biesheuvel <ardb@kernel.org>, Arnd Bergmann <arnd@arndb.de> Cc: linux-arm-kernel@lists.infradead.org, llvm@lists.linux.dev, Linus Walleij <linus.walleij@linaro.org> Subject: [PATCH v4 7/8] ARM: hw_breakpoint: Handle CFI breakpoints Date: Thu, 28 Mar 2024 09:19:30 +0100 [thread overview] Message-ID: <20240328-arm32-cfi-v4-7-a11046139125@linaro.org> (raw) In-Reply-To: <20240328-arm32-cfi-v4-0-a11046139125@linaro.org> This registers a breakpoint handler for the new breakpoint type (0x03) inserted by LLVM CLANG for CFI breakpoints. If we are in permissive mode, just print a backtrace and continue. Example with CONFIG_CFI_PERMISSIVE enabled: > echo CFI_FORWARD_PROTO > /sys/kernel/debug/provoke-crash/DIRECT lkdtm: Performing direct entry CFI_FORWARD_PROTO lkdtm: Calling matched prototype ... lkdtm: Calling mismatched prototype ... CFI failure at lkdtm_indirect_call+0x40/0x4c (target: 0x0; expected type: 0x00000000) WARNING: CPU: 1 PID: 112 at lkdtm_indirect_call+0x40/0x4c CPU: 1 PID: 112 Comm: sh Not tainted 6.8.0-rc1+ #150 Hardware name: ARM-Versatile Express (...) lkdtm: FAIL: survived mismatched prototype function call! lkdtm: Unexpected! This kernel (6.8.0-rc1+ armv7l) was built with CONFIG_CFI_CLANG=y As you can see the LKDTM test fails, but I expect that this would be expected behaviour in the permissive mode. We are currently not implementing target and type for the CFI breakpoint as this requires additional operand bundling compiler extensions. CPUs without breakpoint support cannot handle breakpoints naturally, in these cases the permissive mode will not work, CFI will fall over on an undefined instruction: Internal error: Oops - undefined instruction: 0 [#1] PREEMPT ARM CPU: 0 PID: 186 Comm: ash Tainted: G W 6.9.0-rc1+ #7 Hardware name: Gemini (Device Tree) PC is at lkdtm_indirect_call+0x38/0x4c LR is at lkdtm_CFI_FORWARD_PROTO+0x30/0x6c This is reasonable I think: it's the best CFI can do to ascertain the the control flow is not broken on these CPUs. Signed-off-by: Linus Walleij <linus.walleij@linaro.org> --- arch/arm/include/asm/hw_breakpoint.h | 1 + arch/arm/kernel/hw_breakpoint.c | 30 ++++++++++++++++++++++++++++++ 2 files changed, 31 insertions(+) diff --git a/arch/arm/include/asm/hw_breakpoint.h b/arch/arm/include/asm/hw_breakpoint.h index 62358d3ca0a8..e7f9961c53b2 100644 --- a/arch/arm/include/asm/hw_breakpoint.h +++ b/arch/arm/include/asm/hw_breakpoint.h @@ -84,6 +84,7 @@ static inline void decode_ctrl_reg(u32 reg, #define ARM_DSCR_MOE(x) ((x >> 2) & 0xf) #define ARM_ENTRY_BREAKPOINT 0x1 #define ARM_ENTRY_ASYNC_WATCHPOINT 0x2 +#define ARM_ENTRY_CFI_BREAKPOINT 0x3 #define ARM_ENTRY_SYNC_WATCHPOINT 0xa /* DSCR monitor/halting bits. */ diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c index dc0fb7a81371..ce7c152dd6e9 100644 --- a/arch/arm/kernel/hw_breakpoint.c +++ b/arch/arm/kernel/hw_breakpoint.c @@ -17,6 +17,7 @@ #include <linux/perf_event.h> #include <linux/hw_breakpoint.h> #include <linux/smp.h> +#include <linux/cfi.h> #include <linux/cpu_pm.h> #include <linux/coresight.h> @@ -903,6 +904,32 @@ static void breakpoint_handler(unsigned long unknown, struct pt_regs *regs) watchpoint_single_step_handler(addr); } +#ifdef CONFIG_CFI_CLANG +static void hw_breakpoint_cfi_handler(struct pt_regs *regs) +{ + /* TODO: implementing target and type requires compiler work */ + unsigned long target = 0; + u32 type = 0; + + switch (report_cfi_failure(regs, instruction_pointer(regs), &target, type)) { + case BUG_TRAP_TYPE_BUG: + die("Oops - CFI", regs, 0); + break; + case BUG_TRAP_TYPE_WARN: + /* Skip the breaking instruction */ + instruction_pointer(regs) += 4; + break; + default: + die("Unknown CFI error", regs, 0); + break; + } +} +#else +static void hw_breakpoint_cfi_handler(struct pt_regs *regs) +{ +} +#endif + /* * Called from either the Data Abort Handler [watchpoint] or the * Prefetch Abort Handler [breakpoint] with interrupts disabled. @@ -932,6 +959,9 @@ static int hw_breakpoint_pending(unsigned long addr, unsigned int fsr, case ARM_ENTRY_SYNC_WATCHPOINT: watchpoint_handler(addr, fsr, regs); break; + case ARM_ENTRY_CFI_BREAKPOINT: + hw_breakpoint_cfi_handler(regs); + break; default: ret = 1; /* Unhandled fault. */ } -- 2.44.0 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2024-03-28 8:19 UTC|newest] Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top 2024-03-28 8:19 [PATCH v4 0/8] CFI for ARM32 using LLVM Linus Walleij 2024-03-28 8:19 ` Linus Walleij 2024-03-28 8:19 ` [PATCH v4 1/8] ARM: bugs: Check in the vtable instead of defined aliases Linus Walleij 2024-03-28 8:19 ` Linus Walleij 2024-03-28 8:19 ` [PATCH v4 2/8] ARM: ftrace: Define ftrace_stub_graph Linus Walleij 2024-03-28 8:19 ` Linus Walleij 2024-03-28 8:19 ` [PATCH v4 3/8] ARM: mm: Make tlbflush routines CFI safe Linus Walleij 2024-03-28 8:19 ` Linus Walleij 2024-03-28 8:19 ` [PATCH v4 4/8] ARM: mm: Rewrite cacheflush vtables in CFI safe C Linus Walleij 2024-03-28 8:19 ` [PATCH v4 5/8] ARM: mm: Define prototypes for all per-processor calls Linus Walleij 2024-03-28 8:19 ` Linus Walleij 2024-03-28 8:19 ` [PATCH v4 6/8] ARM: lib: Annotate loop delay instructions for CFI Linus Walleij 2024-03-28 8:19 ` Linus Walleij 2024-03-28 8:19 ` Linus Walleij [this message] 2024-03-28 8:19 ` [PATCH v4 7/8] ARM: hw_breakpoint: Handle CFI breakpoints Linus Walleij 2024-04-04 21:26 ` Kees Cook 2024-04-04 21:26 ` Kees Cook 2024-03-28 8:19 ` [PATCH v4 8/8] ARM: Support CLANG CFI Linus Walleij 2024-03-28 8:19 ` Linus Walleij 2024-04-04 21:27 ` [PATCH v4 0/8] CFI for ARM32 using LLVM Kees Cook 2024-04-04 21:27 ` Kees Cook 2024-04-12 7:38 ` Linus Walleij 2024-04-12 7:38 ` Linus Walleij 2024-04-12 22:07 ` Nathan Chancellor 2024-04-12 22:07 ` Nathan Chancellor
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