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Revision 5f56a74cc0a6d9b9f8ba89cea29cd7c4774cb2b1 authored by Ard Biesheuvel on 20 September 2022, 15:08:23 UTC, committed by Ard Biesheuvel on 22 September 2022, 08:15:44 UTC 
efi: libstub: check Shim mode using MokSBStateRT
 
We currently check the MokSBState variable to decide whether we should
treat UEFI secure boot as being disabled, even if the firmware thinks
otherwise. This is used by shim to indicate that it is not checking
signatures on boot images. In the kernel, we use this to relax lockdown
policies.

However, in cases where shim is not even being used, we don't want this
variable to interfere with lockdown, given that the variable may be
non-volatile and therefore persist across a reboot. This means setting
it once will persistently disable lockdown checks on a given system.

So switch to the mirrored version of this variable, called MokSBStateRT,
which is supposed to be volatile, and this is something we can check.

Cc: <stable@vger.kernel.org> # v4.19+
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Peter Jones <pjones@redhat.com>
1 parent 63bf28c
Raw File
failslab.c 
// SPDX-License-Identifier: GPL-2.0
#include <linux/fault-inject.h>
#include <linux/slab.h>
#include <linux/mm.h>
#include "slab.h"

static struct {
	struct fault_attr attr;
	bool ignore_gfp_reclaim;
	bool cache_filter;
} failslab = {
	.attr = FAULT_ATTR_INITIALIZER,
	.ignore_gfp_reclaim = true,
	.cache_filter = false,
};

bool __should_failslab(struct kmem_cache *s, gfp_t gfpflags)
{
	/* No fault-injection for bootstrap cache */
	if (unlikely(s == kmem_cache))
		return false;

	if (gfpflags & __GFP_NOFAIL)
		return false;

	if (failslab.ignore_gfp_reclaim &&
			(gfpflags & __GFP_DIRECT_RECLAIM))
		return false;

	if (failslab.cache_filter && !(s->flags & SLAB_FAILSLAB))
		return false;

	if (gfpflags & __GFP_NOWARN)
		failslab.attr.no_warn = true;

	return should_fail(&failslab.attr, s->object_size);
}

static int __init setup_failslab(char *str)
{
	return setup_fault_attr(&failslab.attr, str);
}
__setup("failslab=", setup_failslab);

#ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
static int __init failslab_debugfs_init(void)
{
	struct dentry *dir;
	umode_t mode = S_IFREG | 0600;

	dir = fault_create_debugfs_attr("failslab", NULL, &failslab.attr);
	if (IS_ERR(dir))
		return PTR_ERR(dir);

	debugfs_create_bool("ignore-gfp-wait", mode, dir,
			    &failslab.ignore_gfp_reclaim);
	debugfs_create_bool("cache-filter", mode, dir,
			    &failslab.cache_filter);

	return 0;
}

late_initcall(failslab_debugfs_init);

#endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */
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