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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
io-mapping.c 
// SPDX-License-Identifier: GPL-2.0-only

#include <linux/mm.h>
#include <linux/io-mapping.h>

/**
 * io_mapping_map_user - remap an I/O mapping to userspace
 * @iomap: the source io_mapping
 * @vma: user vma to map to
 * @addr: target user address to start at
 * @pfn: physical address of kernel memory
 * @size: size of map area
 *
 *  Note: this is only safe if the mm semaphore is held when called.
 */
int io_mapping_map_user(struct io_mapping *iomap, struct vm_area_struct *vma,
		unsigned long addr, unsigned long pfn, unsigned long size)
{
	vm_flags_t expected_flags = VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;

	if (WARN_ON_ONCE((vma->vm_flags & expected_flags) != expected_flags))
		return -EINVAL;

	/* We rely on prevalidation of the io-mapping to skip track_pfn(). */
	return remap_pfn_range_notrack(vma, addr, pfn, size,
		__pgprot((pgprot_val(iomap->prot) & _PAGE_CACHE_MASK) |
			 (pgprot_val(vma->vm_page_prot) & ~_PAGE_CACHE_MASK)));
}
EXPORT_SYMBOL_GPL(io_mapping_map_user);
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