ANDROID: android: Create debug_symbols driver

Introduce new API to expose symbols useful for debugging the GKI kernel.
Symbols exported from this driver would be difficult to maintain via the
traditional EXPORT_SYMBOL_GPL.

Bug: 199236943
Change-Id: I1cadb409289ca9ce36b0084efc9ac46f6bec6741
Signed-off-by: Elliot Berman <eberman@codeaurora.org>
Signed-off-by: Prasad Sodagudi <psodagud@codeaurora.org>
Signed-off-by: Yogesh Lal <ylal@codeaurora.org>

drivers/android/Kconfig

@@ -54,6 +54,17 @@ config ANDROID_BINDER_IPC_SELFTEST
 	  exhaustively with combinations of various buffer sizes and
 	  alignments.
 
+config ANDROID_DEBUG_SYMBOLS
+	bool "Android Debug Symbols"
+	help
+	  Enables export of debug symbols that are useful for offline debugging
+	  of a kernel. These symbols would be used in vendor modules to find
+	  addresses of the core kernel symbols for vendor extensions.
+
+	  This driver is statically compiled into kernel and maintains all the
+	  required symbol addresses for vendor modules and provides necessary
+	  interface vendor modules.
+
 config ANDROID_VENDOR_HOOKS
 	bool "Android Vendor Hooks"
 	depends on TRACEPOINTS

drivers/android/Makefile

@@ -4,4 +4,5 @@ ccflags-y += -I$(src)			# needed for trace events
 obj-$(CONFIG_ANDROID_BINDERFS)		+= binderfs.o
 obj-$(CONFIG_ANDROID_BINDER_IPC)	+= binder.o binder_alloc.o
 obj-$(CONFIG_ANDROID_BINDER_IPC_SELFTEST) += binder_alloc_selftest.o
+obj-$(CONFIG_ANDROID_DEBUG_SYMBOLS)	+= android_debug_symbols.o
 obj-$(CONFIG_ANDROID_VENDOR_HOOKS) += vendor_hooks.o

drivers/android/android_debug_symbols.c

@@ -0,0 +1,145 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+/*
+ * Copyright (c) 2021, The Linux Foundation. All rights reserved.
+ */
+
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/android_debug_symbols.h>
+#include <asm/stacktrace.h>
+#include <asm/sections.h>
+
+#include <linux/cma.h>
+#include "../../mm/slab.h"
+#include <linux/memblock.h>
+#include <linux/page_owner.h>
+#include <linux/swap.h>
+#include <linux/mm.h>
+#include <linux/security.h>
+
+struct ads_entry {
+	char *name;
+	void *addr;
+};
+
+bool ads_page_owner;
+bool ads_slub_debug;
+unsigned long ads_vmalloc_nr_pages;
+unsigned long ads_pcpu_nr_pages;
+
+#define _ADS_ENTRY(index, symbol)			\
+	[index] = { .name = #symbol, .addr = (void *)symbol }
+#define ADS_ENTRY(index, symbol) _ADS_ENTRY(index, symbol)
+
+#define _ADS_PER_CPU_ENTRY(index, symbol)			\
+	[index] = { .name = #symbol, .addr = (void *)&symbol }
+#define ADS_PER_CPU_ENTRY(index, symbol) _ADS_PER_CPU_ENTRY(index, symbol)
+
+/*
+ * This module maintains static array of symbol and address information.
+ * Add all required core kernel symbols and their addresses into ads_entries[] array,
+ * so that vendor modules can query and to find address of non-exported symbol.
+ */
+static const struct ads_entry ads_entries[ADS_END] = {
+	ADS_ENTRY(ADS_SDATA, _sdata),
+	ADS_ENTRY(ADS_BSS_END, __bss_stop),
+	ADS_ENTRY(ADS_PER_CPU_START, __per_cpu_start),
+	ADS_ENTRY(ADS_PER_CPU_END, __per_cpu_end),
+	ADS_ENTRY(ADS_START_RO_AFTER_INIT, __start_ro_after_init),
+	ADS_ENTRY(ADS_END_RO_AFTER_INIT, __end_ro_after_init),
+	ADS_ENTRY(ADS_LINUX_BANNER, linux_banner),
+#ifdef CONFIG_CMA
+	ADS_ENTRY(ADS_TOTAL_CMA, &totalcma_pages),
+#endif
+	ADS_ENTRY(ADS_SLAB_CACHES, &slab_caches),
+	ADS_ENTRY(ADS_SLAB_MUTEX, &slab_mutex),
+	ADS_ENTRY(ADS_MIN_LOW_PFN, &min_low_pfn),
+	ADS_ENTRY(ADS_MAX_PFN, &max_pfn),
+	ADS_ENTRY(ADS_VMALLOC_NR_PAGES, &ads_vmalloc_nr_pages),
+	ADS_ENTRY(ADS_PCPU_NR_PAGES, &ads_pcpu_nr_pages),
+#ifdef CONFIG_PAGE_OWNER
+	ADS_ENTRY(ADS_PAGE_OWNER_ENABLED, &ads_page_owner),
+#endif
+#ifdef CONFIG_SLUB_DEBUG
+	ADS_ENTRY(ADS_SLUB_DEBUG, &ads_slub_debug),
+#endif
+#ifdef CONFIG_SWAP
+	ADS_ENTRY(ADS_NR_SWAP_PAGES, &nr_swap_pages),
+#endif
+#ifdef CONFIG_MMU
+	ADS_ENTRY(ADS_MMAP_MIN_ADDR, &mmap_min_addr),
+#endif
+	ADS_ENTRY(ADS_STACK_GUARD_GAP, &stack_guard_gap),
+#ifdef CONFIG_SYSCTL
+	ADS_ENTRY(ADS_SYSCTL_LEGACY_VA_LAYOUT, &sysctl_legacy_va_layout),
+#endif
+};
+
+/*
+ * ads_per_cpu_entries array contains all the per_cpu variable address information.
+ */
+static const struct ads_entry ads_per_cpu_entries[ADS_DEBUG_PER_CPU_END] = {
+#ifdef CONFIG_ARM64
+	ADS_PER_CPU_ENTRY(ADS_IRQ_STACK_PTR, irq_stack_ptr),
+#endif
+#ifdef CONFIG_X86
+	ADS_PER_CPU_ENTRY(ADS_IRQ_STACK_PTR, hardirq_stack_ptr),
+#endif
+};
+
+/*
+ * android_debug_symbol - Provide address inforamtion of debug symbol.
+ * @symbol: Index of debug symbol array.
+ *
+ * Return address of core kernel symbol on success and a negative errno will be
+ * returned in error cases.
+ *
+ */
+void *android_debug_symbol(enum android_debug_symbol symbol)
+{
+	if (symbol >= ADS_END)
+		return ERR_PTR(-EINVAL);
+
+	return ads_entries[symbol].addr;
+}
+EXPORT_SYMBOL_NS_GPL(android_debug_symbol, MINIDUMP);
+
+/*
+ * android_debug_per_cpu_symbol - Provide address inforamtion of per cpu debug symbol.
+ * @symbol: Index of per cpu debug symbol array.
+ *
+ * Return address of core kernel symbol on success and a negative errno will be
+ * returned in error cases.
+ *
+ */
+void *android_debug_per_cpu_symbol(enum android_debug_per_cpu_symbol symbol)
+{
+	if (symbol >= ADS_DEBUG_PER_CPU_END)
+		return ERR_PTR(-EINVAL);
+
+	return ads_per_cpu_entries[symbol].addr;
+}
+EXPORT_SYMBOL_NS_GPL(android_debug_per_cpu_symbol, MINIDUMP);
+
+static int __init debug_symbol_init(void)
+{
+#ifdef CONFIG_PAGE_OWNER
+	ads_page_owner  = page_owner_ops.need();
+#endif
+#ifdef CONFIG_SLUB_DEBUG
+	ads_slub_debug = __slub_debug_enabled();
+#endif
+	ads_vmalloc_nr_pages = vmalloc_nr_pages();
+	ads_pcpu_nr_pages = pcpu_nr_pages();
+	return 0;
+}
+module_init(debug_symbol_init);
+
+static void __exit debug_symbol_exit(void)
+{ }
+module_exit(debug_symbol_exit);
+
+MODULE_DESCRIPTION("Debug Symbol Driver");
+MODULE_LICENSE("GPL v2");

include/linux/android_debug_symbols.h

@@ -0,0 +1,73 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (c) 2021, The Linux Foundation. All rights reserved.
+ */
+
+#ifndef _ANDROID_DEBUG_SYMBOLS_H
+#define _ANDROID_DEBUG_SYMBOLS_H
+
+enum android_debug_symbol {
+	ADS_SDATA = 0,
+	ADS_BSS_END,
+	ADS_PER_CPU_START,
+	ADS_PER_CPU_END,
+	ADS_START_RO_AFTER_INIT,
+	ADS_END_RO_AFTER_INIT,
+	ADS_LINUX_BANNER,
+#ifdef CONFIG_CMA
+	ADS_TOTAL_CMA,
+#endif
+	ADS_SLAB_CACHES,
+	ADS_SLAB_MUTEX,
+	ADS_MIN_LOW_PFN,
+	ADS_MAX_PFN,
+	ADS_VMALLOC_NR_PAGES,
+	ADS_PCPU_NR_PAGES,
+#ifdef CONFIG_PAGE_OWNER
+	ADS_PAGE_OWNER_ENABLED,
+#endif
+#ifdef CONFIG_SLUB_DEBUG
+	ADS_SLUB_DEBUG,
+#endif
+#ifdef CONFIG_SWAP
+	ADS_NR_SWAP_PAGES,
+#endif
+#ifdef CONFIG_MMU
+	ADS_MMAP_MIN_ADDR,
+#endif
+	ADS_STACK_GUARD_GAP,
+#ifdef CONFIG_SYSCTL
+	ADS_SYSCTL_LEGACY_VA_LAYOUT,
+#endif
+	ADS_END
+};
+
+enum android_debug_per_cpu_symbol {
+	ADS_IRQ_STACK_PTR = 0,
+	ADS_DEBUG_PER_CPU_END
+};
+
+#ifdef CONFIG_ANDROID_DEBUG_SYMBOLS
+
+void *android_debug_symbol(enum android_debug_symbol symbol);
+void *android_debug_per_cpu_symbol(enum android_debug_per_cpu_symbol symbol);
+
+void android_debug_for_each_module(int (*fn)(const char *mod_name, void *mod_addr, void *data),
+	void *data);
+
+#else /* !CONFIG_ANDROID_DEBUG_SYMBOLS */
+
+static inline void *android_debug_symbol(enum android_debug_symbol symbol)
+{
+	return NULL;
+}
+static inline void *android_debug_per_cpu_symbol(enum android_debug_per_cpu_symbol symbol)
+{
+	return NULL;
+}
+
+static inline void android_debug_for_each_module(int (*fn)(const char *mod_name, void *mod_addr,
+	void *data), void *data) {}
+#endif /* CONFIG_ANDROID_DEBUG_SYMBOLS */
+
+#endif /* _ANDROID_DEBUG_SYMBOLS_H */

kernel/module.c

@@ -4785,6 +4785,22 @@ void print_modules(void)
 	pr_cont("\n");
 }
 
+#ifdef CONFIG_ANDROID_DEBUG_SYMBOLS
+void android_debug_for_each_module(int (*fn)(const char *mod_name, void *mod_addr, void *data),
+	void *data)
+{
+	struct module *module;
+	preempt_disable();
+	list_for_each_entry_rcu(module, &modules, list) {
+		if (fn(module->name, module->core_layout.base, data))
+			goto out;
+	}
+out:
+	preempt_enable();
+}
+EXPORT_SYMBOL_NS_GPL(android_debug_for_each_module, MINIDUMP);
+#endif
+
 #ifdef CONFIG_MODVERSIONS
 /*
  * Generate the signature for all relevant module structures here.