alternate_debugger.c   [plain text]

/*
 * Copyright (c) 2012 Apple Inc. All rights reserved.
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 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
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 * may not be used to create, or enable the creation or redistribution of,
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 * 
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 * 
 * The Original Code and all software distributed under the License are
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 */

#if ALTERNATE_DEBUGGER

/*

The alternate debugger feature is enabled by setting the boot arg "alternate_debugger_init"
to the size of memory that should be set aside for the debugger.  The boot arg
"alternate_debugger_init_pages" is used to allocate more vmpages that the alternate debugger
may use to do additional VA->PA mappings. The boot-arg "alternate_debugger_pause_for_load_at_boot"
will halt the system so that the debugger can be loaded early in the boot cycle -- once the
alternate debugger code is loaded, a register must be set to a 1 to continue the boot process.

Here's an example:
nvram boot-arg="alternate_debugger_init=0x800000 alternate_debugger_init_pages=0x8000 alternate_debugger_pause_for_load_at_boot=1"

The low memory global lgAltDebugger will contain the address of the allocated memory for 
the alternate debugger.  On arm64, the address of this low memory global is 0xffffff8000002048.

At any point after the low memory global is non-zero, Astris may be used to halt the cpu
and load the alternate debugger:

If no alternate debugger is given, but alternate_debugger_init has been specified, and the 
kernel debugger is entered, the string ">MT<" is printed and normal processing continues.

Anytime the alternate debugger is entered, the osversion string is modified to start with "ALT"
so that panic reports can clearly indicated that some kernel poking may have occurred, and
the panic should be weighted accordingly.

*/ 

#include <arm64/alternate_debugger.h>

#include <kern/kalloc.h>
#include <arm64/lowglobals.h>
#include <arm/caches_internal.h>
#include <kern/cpu_data.h>
#include <arm/pmap.h>
#include <pexpert/pexpert.h>
#include <vm/vm_map.h>
#include <vm/vm_kern.h>
#include <libkern/version.h>

void kprintf(const char *fmt, ...);


static mach_vm_address_t alt_code;
static mach_vm_size_t    alt_size;
static mach_vm_address_t alt_pages;
static mach_vm_size_t    alt_pages_size;

typedef void (*t_putc_fn)(char c);
typedef void (*t_call_altdbg_fn)(mach_vm_size_t size, mach_vm_address_t pages, mach_vm_size_t pages_size, t_putc_fn putc_address );

// used as a temporary alternate debugger until another is loaded 
extern void alternate_debugger_just_return(__unused mach_vm_size_t size, __unused mach_vm_address_t pages, __unused mach_vm_size_t pages_size, t_putc_fn putc_address);
extern void *alternate_debugger_just_return_end;

// public entry to the alternate debugger
void alternate_debugger_enter(void)
{
	if ( alt_code != 0 ) {
		disable_preemption();

		printf("########## Going to call ALTERNATE DEBUGGER\n");

		// make sure it isn't in the cache
		assert((alt_size & 0xFFFFFFFF00000000) == 0);
		flush_dcache(alt_code, (unsigned int)alt_size, 0);

		// set the code to execute
		pmap_protect(kernel_map->pmap, alt_code, alt_code+alt_size, VM_PROT_READ|VM_PROT_EXECUTE);

		// black-spot the OS version for any panic reports that occur because of entering the alternate debugger
		if ( *osversion ) {
			memcpy(osversion, "ALT", 3);        // Version set, stomp on the begining of it
		} else {
			strncpy(osversion, "ALT - Version Not Set Yet", OSVERSIZE);
		}

		kprintf("########## Calling ALTERNATE DEBUGGER (size %lld, pages 0x%llx, pages_size 0x%llx, putc %p\n", alt_size, alt_pages, alt_pages_size, &consdebug_putc_unbuffered);
		((t_call_altdbg_fn)alt_code)(alt_size, alt_pages, alt_pages_size, &consdebug_putc_unbuffered);
		kprintf("########## Returned from calling ALTERNATE DEBUGGER\n");

		enable_preemption();
	}
}

// public entry to check boot args and init accordingly
void alternate_debugger_init(void)
{
	// use the alternate debugger
	if( PE_parse_boot_argn("alternate_debugger_init", (void*)&alt_size, sizeof(alt_size)) )
	{
		vm_offset_t     alt_va = 0;

		kprintf("########## ALTERNATE_DEBUGGER\n");

		PE_parse_boot_argn("alternate_debugger_init_pages", (void*)&alt_pages_size, sizeof(alt_pages_size));

		alt_size = vm_map_round_page(alt_size,
					     VM_MAP_PAGE_MASK(kernel_map));
		alt_pages_size = vm_map_round_page(alt_pages_size,
						   VM_MAP_PAGE_MASK(kernel_map));

		kern_return_t kr = KERN_SUCCESS;
		kr = kmem_alloc_contig(kernel_map, &alt_va, alt_size, VM_MAP_PAGE_MASK(kernel_map), 0, 0, KMA_NOPAGEWAIT | KMA_KOBJECT | KMA_LOMEM, VM_KERN_MEMORY_DIAG);
		if( kr != KERN_SUCCESS)
		{
			kprintf("########## ALTERNATE_DEBUGGER FAILED kmem_alloc_contig with %d\n", kr);
			alt_va = 0;
		}
		else {
			if ( alt_pages_size ) {
				alt_pages = (vm_offset_t) kalloc((vm_size_t) alt_pages_size);
			}
		}

		kprintf("########## Initializing ALTERNATE DEBUGGER : [alloc size 0x%llx @0x%lx] [pages_size 0x%llx @0x%llx] -- lowmem pointer at %p\n",
					alt_size, alt_va, alt_pages_size, alt_pages, &lowGlo.lgAltDebugger );

		if ( alt_va ) {
			uintptr_t just_return_size = (uintptr_t)&alternate_debugger_just_return_end - (uintptr_t)&alternate_debugger_just_return;
			assert(just_return_size <= alt_size); // alt_size is page-rounded, just_return_size should be much less than a page.
			// install a simple return vector
			memcpy((void*)alt_va, &alternate_debugger_just_return, just_return_size);

			// code is ready, enable the pointers to it
			lowGlo.lgAltDebugger = alt_code = alt_va;

#if 1
			// DEBUG for BRING-UP testing
			unsigned int alt_init_test;
			if(PE_parse_boot_argn("alternate_debugger_pause_for_load_at_boot", &alt_init_test, sizeof(alt_init_test)) ) {

				// debug!!
				kprintf("########## Waiting for ALTERNATE DEBUGGER to load (in file %s).... to continue, set register to 1", __FILE__ );
				volatile int ii = 0;
				while(!ii)
					;
				kprintf("\n");
				alternate_debugger_enter();
			}
#endif
		}
	}
}

#endif /* ALTERNATE_DEBUGGER */