Updates for KCOV instrumentation on x86:

- Prevent spurious KCOV coverage in common_interrupt() - Fixup the KCOV Makefile directive which got stale due to a source file rename - Exclude stack unwinding from KCOV as it creates large amounts of uninteresting coverage - Provide a self test to validate that KCOV coverage of the interrupt handling code starts not before preempt count got updated. -----BEGIN PGP SIGNATURE----- iQJHBAABCgAxFiEEQp8+kY+LLUocC4bMphj1TA10mKEFAmbpMeITHHRnbHhAbGlu dXRyb25peC5kZQAKCRCmGPVMDXSYoaOeD/4oO3g0soK0LIcDIwzaG0ap0hx0nucw aVSAESuY+ZaSbRbV0fNoYdHORvLdErs67SeyeJRSxTzSNqGH2dGoFrfbkRSXq951 RdCSPP60T7xgqAme1YLDiChfXt/gkbWk/8V5Q7sG3oq3GaVcPUyZgPo4M4HQMdfg Mla3VPikW5Np3fvs0IZYWQ5VdY0fFOHY5JGMhKJznJxf+Ud+VAtxsbJUcO4MEYWW A9CVJNHGEXssGA6vm5kgtLu6n2QFuoSj6En/WqLEaJb8f/V332e04Xj2ZHUaOOjV 2abVeDovv+dwUYb4SgrGVg9gfEwwcLPDnmOuuQJmQBB5kU4mJsCqI5TTS6c1fgU4 x8tQsGSOKHFQAI14ZWtitrL4rS2uFcBkAFXo0dF8J5o4989RA8cpfeWVSVUb/UXd u38BWpc9iHiihHKMmMQgsa1bUMwdSUTvN5XFHkeP4oqUdMiEiWn8iM5+zXd/lfTs 9mrTv+kcLA7mjFOmn4JyE2b+NuiPdgS2FCBGLycHvGwvJoJlO2UmSpF89AJ5vdKs F8vWLkV+gno/HtwS5o949cAwjYiCodfc7u1W0xj2VDAbx0RbaBw1SDhXMQcLxLgn BTt4yHKKIeLX++WH3fpeyL91+UJWubUzNzY4rAmLkz5DedWAkpES+45fatp1buIz Lp/hGiIsG9p5xw== =tiXT -----END PGP SIGNATURE----- Merge tag 'x86-build-2024-09-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull x86 build updates from Thomas Gleixner: "Updates for KCOV instrumentation on x86: - Prevent spurious KCOV coverage in common_interrupt() - Fixup the KCOV Makefile directive which got stale due to a source file rename - Exclude stack unwinding from KCOV as it creates large amounts of uninteresting coverage - Provide a self test to validate that KCOV coverage of the interrupt handling code starts not before preempt count got updated" * tag 'x86-build-2024-09-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: x86: Ignore stack unwinding in KCOV module: Fix KCOV-ignored file name kcov: Add interrupt handling self test x86/entry: Remove unwanted instrumentation in common_interrupt()
2024-11-01 04:53:36 +01:00 · 2024-09-17 12:40:34 +02:00 · 2024-09-17 12:40:34 +02:00 · 5ba202a7c9
commit 5ba202a7c9
parent a940d9a43e ae94b263f5
6 changed files with 57 additions and 6 deletions
--- a/arch/x86/include/asm/hardirq.h
+++ b/arch/x86/include/asm/hardirq.h
@ -69,7 +69,11 @@ extern u64 arch_irq_stat(void);
 #define local_softirq_pending_ref       pcpu_hot.softirq_pending

 #if IS_ENABLED(CONFIG_KVM_INTEL)
-static inline void kvm_set_cpu_l1tf_flush_l1d(void)
+/*
+ * This function is called from noinstr interrupt contexts
+ * and must be inlined to not get instrumentation.
+ */
+static __always_inline void kvm_set_cpu_l1tf_flush_l1d(void)
 {
 	__this_cpu_write(irq_stat.kvm_cpu_l1tf_flush_l1d, 1);
 }
@ -84,7 +88,7 @@ static __always_inline bool kvm_get_cpu_l1tf_flush_l1d(void)
 	return __this_cpu_read(irq_stat.kvm_cpu_l1tf_flush_l1d);
 }
 #else /* !IS_ENABLED(CONFIG_KVM_INTEL) */
-static inline void kvm_set_cpu_l1tf_flush_l1d(void) { }
+static __always_inline void kvm_set_cpu_l1tf_flush_l1d(void) { }
 #endif /* IS_ENABLED(CONFIG_KVM_INTEL) */

 #endif /* _ASM_X86_HARDIRQ_H */
--- a/arch/x86/include/asm/idtentry.h
+++ b/arch/x86/include/asm/idtentry.h
@ -212,8 +212,8 @@ __visible noinstr void func(struct pt_regs *regs,			\
 	irqentry_state_t state = irqentry_enter(regs);			\
 	u32 vector = (u32)(u8)error_code;				\
 									\
+	kvm_set_cpu_l1tf_flush_l1d();                                   \
 	instrumentation_begin();					\
-	kvm_set_cpu_l1tf_flush_l1d();					\
 	run_irq_on_irqstack_cond(__##func, regs, vector);		\
 	instrumentation_end();						\
 	irqentry_exit(regs, state);					\
@ -250,7 +250,6 @@ static void __##func(struct pt_regs *regs);				\
 									\
 static __always_inline void instr_##func(struct pt_regs *regs)		\
 {									\
-	kvm_set_cpu_l1tf_flush_l1d();					\
 	run_sysvec_on_irqstack_cond(__##func, regs);			\
 }									\
 									\
@ -258,6 +257,7 @@ __visible noinstr void func(struct pt_regs *regs)			\
 {									\
 	irqentry_state_t state = irqentry_enter(regs);			\
 									\
+	kvm_set_cpu_l1tf_flush_l1d();                                   \
 	instrumentation_begin();					\
 	instr_##func (regs);						\
 	instrumentation_end();						\
@ -288,7 +288,6 @@ static __always_inline void __##func(struct pt_regs *regs);		\
 static __always_inline void instr_##func(struct pt_regs *regs)		\
 {									\
 	__irq_enter_raw();						\
-	kvm_set_cpu_l1tf_flush_l1d();					\
 	__##func (regs);						\
 	__irq_exit_raw();						\
 }									\
@ -297,6 +296,7 @@ __visible noinstr void func(struct pt_regs *regs)			\
 {									\
 	irqentry_state_t state = irqentry_enter(regs);			\
 									\
+	kvm_set_cpu_l1tf_flush_l1d();                                   \
 	instrumentation_begin();					\
 	instr_##func (regs);						\
 	instrumentation_end();						\
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@ -35,6 +35,14 @@ KMSAN_SANITIZE_nmi.o					:= n
 # If instrumentation of the following files is enabled, boot hangs during
 # first second.
 KCOV_INSTRUMENT_head$(BITS).o				:= n
+# These are called from save_stack_trace() on debug paths,
+# and produce large amounts of uninteresting coverage.
+KCOV_INSTRUMENT_stacktrace.o				:= n
+KCOV_INSTRUMENT_dumpstack.o				:= n
+KCOV_INSTRUMENT_dumpstack_$(BITS).o			:= n
+KCOV_INSTRUMENT_unwind_orc.o				:= n
+KCOV_INSTRUMENT_unwind_frame.o				:= n
+KCOV_INSTRUMENT_unwind_guess.o				:= n

 CFLAGS_irq.o := -I $(src)/../include/asm/trace

--- a/kernel/kcov.c
+++ b/kernel/kcov.c
@ -11,6 +11,7 @@
 #include <linux/fs.h>
 #include <linux/hashtable.h>
 #include <linux/init.h>
+#include <linux/jiffies.h>
 #include <linux/kmsan-checks.h>
 #include <linux/mm.h>
 #include <linux/preempt.h>
@ -1067,6 +1068,32 @@ u64 kcov_common_handle(void)
 }
 EXPORT_SYMBOL(kcov_common_handle);

+#ifdef CONFIG_KCOV_SELFTEST
+static void __init selftest(void)
+{
+	unsigned long start;
+
+	pr_err("running self test\n");
+	/*
+	 * Test that interrupts don't produce spurious coverage.
+	 * The coverage callback filters out interrupt code, but only
+	 * after the handler updates preempt count. Some code periodically
+	 * leaks out of that section and leads to spurious coverage.
+	 * It's hard to call the actual interrupt handler directly,
+	 * so we just loop here for a bit waiting for a timer interrupt.
+	 * We set kcov_mode to enable tracing, but don't setup the area,
+	 * so any attempt to trace will crash. Note: we must not call any
+	 * potentially traced functions in this region.
+	 */
+	start = jiffies;
+	current->kcov_mode = KCOV_MODE_TRACE_PC;
+	while ((jiffies - start) * MSEC_PER_SEC / HZ < 300)
+		;
+	current->kcov_mode = 0;
+	pr_err("done running self test\n");
+}
+#endif
+
 static int __init kcov_init(void)
 {
 	int cpu;
@ -1086,6 +1113,10 @@ static int __init kcov_init(void)
 	 */
 	debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops);

+#ifdef CONFIG_KCOV_SELFTEST
+	selftest();
+#endif
+
 	return 0;
 }

--- a/kernel/module/Makefile
+++ b/kernel/module/Makefile
@ -5,7 +5,7 @@

 # These are called from save_stack_trace() on slub debug path,
 # and produce insane amounts of uninteresting coverage.
-KCOV_INSTRUMENT_module.o := n
+KCOV_INSTRUMENT_main.o := n

 obj-y += main.o
 obj-y += strict_rwx.o
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@ -2173,6 +2173,14 @@ config KCOV_IRQ_AREA_SIZE
 	  soft interrupts. This specifies the size of those areas in the
 	  number of unsigned long words.

+config KCOV_SELFTEST
+	bool "Perform short selftests on boot"
+	depends on KCOV
+	help
+	  Run short KCOV coverage collection selftests on boot.
+	  On test failure, causes the kernel to panic. Recommended to be
+	  enabled, ensuring critical functionality works as intended.
+
 menuconfig RUNTIME_TESTING_MENU
 	bool "Runtime Testing"
 	default y