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Revert r346292 (permit_nonrandom_stackcookies)

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We have a better, more comprehensive knob for this now:
kern.random.initial_seeding.bypass_before_seeding=1.

Requested by:	delphij
Sponsored by:	Dell EMC Isilon
This commit is contained in:
Conrad Meyer 2019-05-13 23:37:44 +00:00
parent b17868a211
commit e199792d23
2 changed files with 3 additions and 55 deletions
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7
UPDATING
View File

@ -75,13 +75,6 @@ NOTE TO PEOPLE WHO THINK THAT FreeBSD 13.x IS SLOW:
met as for the diagnostic sysctls above. Defaults to zero, i.e.,
produce warnings in dmesg when the conditions are met.
20190416:
The tunable "security.stack_protect.permit_nonrandom_cookies" may be
set to a non-zero value to boot systems that do not provide early
entropy. Otherwise, such systems may see the panic message:
"cannot initialize stack cookies because random device is not yet
seeded."
20190416:
The loadable random module KPI has changed; the random_infra_init()
routine now requires a 3rd function pointer for a bool (*)(void)

51
sys/kern/stack_protector.c
View File

@ -4,28 +4,12 @@ __FBSDID("$FreeBSD$");
#include <sys/types.h>
#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/random.h>
#include <sys/sysctl.h>
#include <sys/systm.h>
#include <sys/libkern.h>
long __stack_chk_guard[8] = {};
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
__stack_chk_fail(void)
{
@ -39,37 +23,8 @@ __stack_chk_init(void *dummy __unused)
size_t i;
long guard[nitems(__stack_chk_guard)];
if (is_random_seeded()) {
arc4rand(guard, sizeof(guard), 0);
for (i = 0; i < nitems(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__);
arc4rand(guard, sizeof(guard), 0);
for (i = 0; i < nitems(guard); i++)
__stack_chk_guard[i] = guard[i];
}
SYSINIT(stack_chk, SI_SUB_RANDOM, SI_ORDER_ANY, __stack_chk_init, NULL);