1 files changed, 266 insertions, 0 deletions
diff --git a/common/backtrace/backtrace.c b/common/backtrace/backtrace.c
new file mode 100644
index 0000000..f994ae5
--- /dev/null
+++ b/common/backtrace/backtrace.c
@@ -0,0 +1,266 @@
+/*
+ * Copyright (c) 2018-2022, ARM Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <assert.h>
+#include <stdbool.h>
+#include <stdint.h>
+
+#include <arch_helpers.h>
+#include <common/debug.h>
+#include <drivers/console.h>
+
+/* Maximum number of entries in the backtrace to display */
+#define UNWIND_LIMIT	20U
+
+/*
+ * If -fno-omit-frame-pointer is used:
+ *
+ * - AArch64: The AAPCS defines the format of the frame records and mandates the
+ *   usage of r29 as frame pointer.
+ *
+ * - AArch32: The format of the frame records is not defined in the AAPCS.
+ *   However, at least GCC and Clang use the same format. When they are forced
+ *   to only generate A32 code (with -marm), they use r11 as frame pointer and a
+ *   similar format as in AArch64. If interworking with T32 is enabled, the
+ *   frame pointer is r7 and the format is  different. This is not supported by
+ *   this implementation of backtrace, so it is needed to use -marm.
+ */
+
+/* Frame records form a linked list in the stack */
+struct frame_record {
+	/* Previous frame record in the list */
+	struct frame_record *parent;
+	/* Return address of the function at this level */
+	uintptr_t return_addr;
+};
+
+static inline uintptr_t extract_address(uintptr_t address)
+{
+	uintptr_t ret = address;
+
+#if ENABLE_PAUTH
+	/*
+	 * When pointer authentication is enabled, the LR value saved on the
+	 * stack contains a PAC. It must be stripped to retrieve the return
+	 * address.
+	 */
+
+	xpaci(ret);
+#endif
+
+	return ret;
+}
+
+/*
+ * Returns true if the address points to a virtual address that can be read at
+ * the current EL, false otherwise.
+ */
+#ifdef __aarch64__
+static bool is_address_readable(uintptr_t address)
+{
+	unsigned int el = get_current_el();
+	uintptr_t addr = extract_address(address);
+
+	if (el == 3U) {
+		ats1e3r(addr);
+	} else if (el == 2U) {
+		ats1e2r(addr);
+	} else {
+		AT(ats1e1r, addr);
+	}
+
+	isb();
+
+	/* If PAR.F == 1 the address translation was aborted.  */
+	if ((read_par_el1() & PAR_F_MASK) != 0U)
+		return false;
+
+	return true;
+}
+#else /* !__aarch64__ */
+static bool is_address_readable(uintptr_t addr)
+{
+	unsigned int el = get_current_el();
+
+	if (el == 3U) {
+		write_ats1cpr(addr);
+	} else if (el == 2U) {
+		write_ats1hr(addr);
+	} else {
+		write_ats1cpr(addr);
+	}
+
+	isb();
+
+	/* If PAR.F == 1 the address translation was aborted.  */
+	if ((read64_par() & PAR_F_MASK) != 0U)
+		return false;
+
+	return true;
+}
+#endif /* __aarch64__ */
+
+/*
+ * Returns true if all the bytes in a given object are in mapped memory and an
+ * LDR using this pointer would succeed, false otherwise.
+ */
+static bool is_valid_object(uintptr_t addr, size_t size)
+{
+	assert(size > 0U);
+
+	if (addr == 0U)
+		return false;
+
+	/* Detect overflows */
+	if ((addr + size) < addr)
+		return false;
+
+	/* A pointer not aligned properly could trigger an alignment fault. */
+	if ((addr & (sizeof(uintptr_t) - 1U)) != 0U)
+		return false;
+
+	/* Check that all the object is readable */
+	for (size_t i = 0; i < size; i++) {
+		if (!is_address_readable(addr + i))
+			return false;
+	}
+
+	return true;
+}
+
+/*
+ * Returns true if the specified address is correctly aligned and points to a
+ * valid memory region.
+ */
+static bool is_valid_jump_address(uintptr_t addr)
+{
+	if (addr == 0U)
+		return false;
+
+	/* Check alignment. Both A64 and A32 use 32-bit opcodes */
+	if ((addr & (sizeof(uint32_t) - 1U)) != 0U)
+		return false;
+
+	if (!is_address_readable(addr))
+		return false;
+
+	return true;
+}
+
+/*
+ * Returns true if the pointer points at a valid frame record, false otherwise.
+ */
+static bool is_valid_frame_record(struct frame_record *fr)
+{
+	return is_valid_object((uintptr_t)fr, sizeof(struct frame_record));
+}
+
+/*
+ * Adjust the frame-pointer-register value by 4 bytes on AArch32 to have the
+ * same layout as AArch64.
+ */
+static struct frame_record *adjust_frame_record(struct frame_record *fr)
+{
+#ifdef __aarch64__
+	return fr;
+#else
+	return (struct frame_record *)((uintptr_t)fr - 4U);
+#endif
+}
+
+static void unwind_stack(struct frame_record *fr, uintptr_t current_pc,
+			 uintptr_t link_register)
+{
+	uintptr_t call_site;
+	static const char *backtrace_str = "%u: %s: 0x%lx\n";
+	const char *el_str = get_el_str(get_current_el());
+
+	if (!is_valid_frame_record(fr)) {
+		printf("ERROR: Corrupted frame pointer (frame record address = %p)\n",
+		       fr);
+		return;
+	}
+
+	call_site = extract_address(fr->return_addr);
+	if (call_site != link_register) {
+		printf("ERROR: Corrupted stack (frame record address = %p)\n",
+		       fr);
+		return;
+	}
+
+	/* The level 0 of the backtrace is the current backtrace function */
+	printf(backtrace_str, 0U, el_str, current_pc);
+
+	/*
+	 * The last frame record pointer in the linked list at the beginning of
+	 * the stack should be NULL unless stack is corrupted.
+	 */
+	for (unsigned int i = 1U; i < UNWIND_LIMIT; i++) {
+		/* If an invalid frame record is found, exit. */
+		if (!is_valid_frame_record(fr))
+			return;
+		/*
+		 * A32 and A64 are fixed length so the address from where the
+		 * call was made is the instruction before the return address,
+		 * which is always 4 bytes before it.
+		 */
+
+		call_site = extract_address(fr->return_addr) - 4U;
+
+		/*
+		 * If the address is invalid it means that the frame record is
+		 * probably corrupted.
+		 */
+		if (!is_valid_jump_address(call_site))
+			return;
+
+		printf(backtrace_str, i, el_str, call_site);
+
+		fr = adjust_frame_record(fr->parent);
+	}
+
+	printf("ERROR: Max backtrace depth reached\n");
+}
+
+/*
+ * Display a backtrace. The cookie string parameter is displayed along the
+ * trace to help filter the log messages.
+ *
+ * Many things can prevent displaying the expected backtrace. For example,
+ * compiler optimizations can use a branch instead of branch with link when it
+ * detects a tail call. The backtrace level for this caller will not be
+ * displayed, as it does not appear in the call stack anymore. Also, assembly
+ * functions will not be displayed unless they setup AAPCS compliant frame
+ * records on AArch64 and compliant with GCC-specific frame record format on
+ * AArch32.
+ *
+ * Usage of the trace: addr2line can be used to map the addresses to function
+ * and source code location when given the ELF file compiled with debug
+ * information. The "-i" flag is highly recommended to improve display of
+ * inlined function. The *.dump files generated when building each image can
+ * also be used.
+ *
+ * WARNING: In case of corrupted stack, this function could display security
+ * sensitive information past the beginning of the stack so it must not be used
+ * in production build. This function is only compiled in when ENABLE_BACKTRACE
+ * is set to 1.
+ */
+void backtrace(const char *cookie)
+{
+	uintptr_t return_address = (uintptr_t)__builtin_return_address(0U);
+	struct frame_record *fr = __builtin_frame_address(0U);
+
+	/* Printing the backtrace may crash the system, flush before starting */
+	console_flush();
+
+	fr = adjust_frame_record(fr);
+
+	printf("BACKTRACE: START: %s\n", cookie);
+
+	unwind_stack(fr, (uintptr_t)&backtrace, return_address);
+
+	printf("BACKTRACE: END: %s\n", cookie);
+}