Differential D19927 Diff 56263 head/sys/kern/stack_protector.c

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head/sys/kern/stack_protector.c

	#include <sys/cdefs.h>			#include <sys/cdefs.h>
	__FBSDID("$FreeBSD$");			__FBSDID("$FreeBSD$");

	#include <sys/types.h>			#include <sys/types.h>
	#include <sys/param.h>			#include <sys/param.h>
	#include <sys/kernel.h>			#include <sys/kernel.h>
				#include <sys/random.h>
				#include <sys/sysctl.h>
	#include <sys/systm.h>			#include <sys/systm.h>
	#include <sys/libkern.h>			#include <sys/libkern.h>

	long __stack_chk_guard[8] = {};			long __stack_chk_guard[8] = {};
	void __stack_chk_fail(void);			void __stack_chk_fail(void);

				/*
				* XXX This default is unsafe!!! We intend to change it after resolving issues
				* with early entropy in the installer; some kinds of systems that do not use
				* loader(8), such as riscv, aarch64, and power; and perhaps others that I am
				* forgetting off the top of my head.
				*/
				static bool permit_nonrandom_cookies = true;

				SYSCTL_NODE(_security, OID_AUTO, stack_protect, CTLFLAG_RW, 0,
				"-fstack-protect support");
				SYSCTL_BOOL(_security_stack_protect, OID_AUTO, permit_nonrandom_cookies,
				CTLFLAG_RDTUN, &permit_nonrandom_cookies, 0,
				"Allow stack guard to be used without real random cookies");

	void			void
	__stack_chk_fail(void)			__stack_chk_fail(void)
	{			{

	panic("stack overflow detected; backtrace may be corrupted");			panic("stack overflow detected; backtrace may be corrupted");
	}			}

	static void			static void
	__stack_chk_init(void *dummy __unused)			__stack_chk_init(void *dummy __unused)
	{			{
	size_t i;			size_t i;
	long guard[nitems(__stack_chk_guard)];			long guard[nitems(__stack_chk_guard)];

				if (is_random_seeded()) {
	arc4rand(guard, sizeof(guard), 0);			arc4rand(guard, sizeof(guard), 0);
	for (i = 0; i < nitems(guard); i++)			for (i = 0; i < nitems(guard); i++)
	__stack_chk_guard[i] = guard[i];			__stack_chk_guard[i] = guard[i];
				return;
				}

				if (permit_nonrandom_cookies) {
				printf("%s: WARNING: Initializing stack protection with "
				"non-random cookies!\n", __func__);
				printf("%s: WARNING: This severely limits the benefit of "
				"-fstack-protector!\n", __func__);

				/*
				* The emperor is naked, but I rolled some dice and at least
				* these values aren't zero.
				*/
				__stack_chk_guard[0] = (long)0xe7318d5959af899full;
				__stack_chk_guard[1] = (long)0x35a9481c089348bfull;
				__stack_chk_guard[2] = (long)0xde657fdc04117255ull;
				__stack_chk_guard[3] = (long)0x0dd44c61c22e4a6bull;
				__stack_chk_guard[4] = (long)0x0a5869a354edb0a5ull;
				__stack_chk_guard[5] = (long)0x05cebfed255b5232ull;
				__stack_chk_guard[6] = (long)0x270ffac137c4c72full;
				__stack_chk_guard[7] = (long)0xd8141a789bad478dull;
				_Static_assert(nitems(__stack_chk_guard) == 8,
				"__stack_chk_guard doesn't have 8 items");
				return;
				}

				panic("%s: cannot initialize stack cookies because random device is "
				"not yet seeded", __func__);
	}			}
	SYSINIT(stack_chk, SI_SUB_RANDOM, SI_ORDER_ANY, __stack_chk_init, NULL);			SYSINIT(stack_chk, SI_SUB_RANDOM, SI_ORDER_ANY, __stack_chk_init, NULL);