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
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
page_vma_mapped.c
// SPDX-License-Identifier: GPL-2.0
#include <linux/mm.h>
#include <linux/rmap.h>
#include <linux/hugetlb.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include "internal.h"
static inline bool not_found(struct page_vma_mapped_walk *pvmw)
{
page_vma_mapped_walk_done(pvmw);
return false;
}
static bool map_pte(struct page_vma_mapped_walk *pvmw)
{
pvmw->pte = pte_offset_map(pvmw->pmd, pvmw->address);
if (!(pvmw->flags & PVMW_SYNC)) {
if (pvmw->flags & PVMW_MIGRATION) {
if (!is_swap_pte(*pvmw->pte))
return false;
} else {
/*
* We get here when we are trying to unmap a private
* device page from the process address space. Such
* page is not CPU accessible and thus is mapped as
* a special swap entry, nonetheless it still does
* count as a valid regular mapping for the page (and
* is accounted as such in page maps count).
*
* So handle this special case as if it was a normal
* page mapping ie lock CPU page table and returns
* true.
*
* For more details on device private memory see HMM
* (include/linux/hmm.h or mm/hmm.c).
*/
if (is_swap_pte(*pvmw->pte)) {
swp_entry_t entry;
/* Handle un-addressable ZONE_DEVICE memory */
entry = pte_to_swp_entry(*pvmw->pte);
if (!is_device_private_entry(entry) &&
!is_device_exclusive_entry(entry))
return false;
} else if (!pte_present(*pvmw->pte))
return false;
}
}
pvmw->ptl = pte_lockptr(pvmw->vma->vm_mm, pvmw->pmd);
spin_lock(pvmw->ptl);
return true;
}
/**
* check_pte - check if @pvmw->page is mapped at the @pvmw->pte
* @pvmw: page_vma_mapped_walk struct, includes a pair pte and page for checking
*
* page_vma_mapped_walk() found a place where @pvmw->page is *potentially*
* mapped. check_pte() has to validate this.
*
* pvmw->pte may point to empty PTE, swap PTE or PTE pointing to
* arbitrary page.
*
* If PVMW_MIGRATION flag is set, returns true if @pvmw->pte contains migration
* entry that points to @pvmw->page or any subpage in case of THP.
*
* If PVMW_MIGRATION flag is not set, returns true if pvmw->pte points to
* pvmw->page or any subpage in case of THP.
*
* Otherwise, return false.
*
*/
static bool check_pte(struct page_vma_mapped_walk *pvmw)
{
unsigned long pfn;
if (pvmw->flags & PVMW_MIGRATION) {
swp_entry_t entry;
if (!is_swap_pte(*pvmw->pte))
return false;
entry = pte_to_swp_entry(*pvmw->pte);
if (!is_migration_entry(entry) &&
!is_device_exclusive_entry(entry))
return false;
pfn = swp_offset(entry);
} else if (is_swap_pte(*pvmw->pte)) {
swp_entry_t entry;
/* Handle un-addressable ZONE_DEVICE memory */
entry = pte_to_swp_entry(*pvmw->pte);
if (!is_device_private_entry(entry) &&
!is_device_exclusive_entry(entry))
return false;
pfn = swp_offset(entry);
} else {
if (!pte_present(*pvmw->pte))
return false;
pfn = pte_pfn(*pvmw->pte);
}
return (pfn - pvmw->pfn) < pvmw->nr_pages;
}
/* Returns true if the two ranges overlap. Careful to not overflow. */
static bool check_pmd(unsigned long pfn, struct page_vma_mapped_walk *pvmw)
{
if ((pfn + HPAGE_PMD_NR - 1) < pvmw->pfn)
return false;
if (pfn > pvmw->pfn + pvmw->nr_pages - 1)
return false;
return true;
}
static void step_forward(struct page_vma_mapped_walk *pvmw, unsigned long size)
{
pvmw->address = (pvmw->address + size) & ~(size - 1);
if (!pvmw->address)
pvmw->address = ULONG_MAX;
}
/**
* page_vma_mapped_walk - check if @pvmw->pfn is mapped in @pvmw->vma at
* @pvmw->address
* @pvmw: pointer to struct page_vma_mapped_walk. page, vma, address and flags
* must be set. pmd, pte and ptl must be NULL.
*
* Returns true if the page is mapped in the vma. @pvmw->pmd and @pvmw->pte point
* to relevant page table entries. @pvmw->ptl is locked. @pvmw->address is
* adjusted if needed (for PTE-mapped THPs).
*
* If @pvmw->pmd is set but @pvmw->pte is not, you have found PMD-mapped page
* (usually THP). For PTE-mapped THP, you should run page_vma_mapped_walk() in
* a loop to find all PTEs that map the THP.
*
* For HugeTLB pages, @pvmw->pte is set to the relevant page table entry
* regardless of which page table level the page is mapped at. @pvmw->pmd is
* NULL.
*
* Returns false if there are no more page table entries for the page in
* the vma. @pvmw->ptl is unlocked and @pvmw->pte is unmapped.
*
* If you need to stop the walk before page_vma_mapped_walk() returned false,
* use page_vma_mapped_walk_done(). It will do the housekeeping.
*/
bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw)
{
struct vm_area_struct *vma = pvmw->vma;
struct mm_struct *mm = vma->vm_mm;
unsigned long end;
pgd_t *pgd;
p4d_t *p4d;
pud_t *pud;
pmd_t pmde;
/* The only possible pmd mapping has been handled on last iteration */
if (pvmw->pmd && !pvmw->pte)
return not_found(pvmw);
if (unlikely(is_vm_hugetlb_page(vma))) {
struct hstate *hstate = hstate_vma(vma);
unsigned long size = huge_page_size(hstate);
/* The only possible mapping was handled on last iteration */
if (pvmw->pte)
return not_found(pvmw);
/* when pud is not present, pte will be NULL */
pvmw->pte = huge_pte_offset(mm, pvmw->address, size);
if (!pvmw->pte)
return false;
pvmw->ptl = huge_pte_lock(hstate, mm, pvmw->pte);
if (!check_pte(pvmw))
return not_found(pvmw);
return true;
}
end = vma_address_end(pvmw);
if (pvmw->pte)
goto next_pte;
restart:
do {
pgd = pgd_offset(mm, pvmw->address);
if (!pgd_present(*pgd)) {
step_forward(pvmw, PGDIR_SIZE);
continue;
}
p4d = p4d_offset(pgd, pvmw->address);
if (!p4d_present(*p4d)) {
step_forward(pvmw, P4D_SIZE);
continue;
}
pud = pud_offset(p4d, pvmw->address);
if (!pud_present(*pud)) {
step_forward(pvmw, PUD_SIZE);
continue;
}
pvmw->pmd = pmd_offset(pud, pvmw->address);
/*
* Make sure the pmd value isn't cached in a register by the
* compiler and used as a stale value after we've observed a
* subsequent update.
*/
pmde = READ_ONCE(*pvmw->pmd);
if (pmd_trans_huge(pmde) || is_pmd_migration_entry(pmde) ||
(pmd_present(pmde) && pmd_devmap(pmde))) {
pvmw->ptl = pmd_lock(mm, pvmw->pmd);
pmde = *pvmw->pmd;
if (!pmd_present(pmde)) {
swp_entry_t entry;
if (!thp_migration_supported() ||
!(pvmw->flags & PVMW_MIGRATION))
return not_found(pvmw);
entry = pmd_to_swp_entry(pmde);
if (!is_migration_entry(entry) ||
!check_pmd(swp_offset(entry), pvmw))
return not_found(pvmw);
return true;
}
if (likely(pmd_trans_huge(pmde) || pmd_devmap(pmde))) {
if (pvmw->flags & PVMW_MIGRATION)
return not_found(pvmw);
if (!check_pmd(pmd_pfn(pmde), pvmw))
return not_found(pvmw);
return true;
}
/* THP pmd was split under us: handle on pte level */
spin_unlock(pvmw->ptl);
pvmw->ptl = NULL;
} else if (!pmd_present(pmde)) {
/*
* If PVMW_SYNC, take and drop THP pmd lock so that we
* cannot return prematurely, while zap_huge_pmd() has
* cleared *pmd but not decremented compound_mapcount().
*/
if ((pvmw->flags & PVMW_SYNC) &&
transhuge_vma_suitable(vma, pvmw->address) &&
(pvmw->nr_pages >= HPAGE_PMD_NR)) {
spinlock_t *ptl = pmd_lock(mm, pvmw->pmd);
spin_unlock(ptl);
}
step_forward(pvmw, PMD_SIZE);
continue;
}
if (!map_pte(pvmw))
goto next_pte;
this_pte:
if (check_pte(pvmw))
return true;
next_pte:
do {
pvmw->address += PAGE_SIZE;
if (pvmw->address >= end)
return not_found(pvmw);
/* Did we cross page table boundary? */
if ((pvmw->address & (PMD_SIZE - PAGE_SIZE)) == 0) {
if (pvmw->ptl) {
spin_unlock(pvmw->ptl);
pvmw->ptl = NULL;
}
pte_unmap(pvmw->pte);
pvmw->pte = NULL;
goto restart;
}
pvmw->pte++;
if ((pvmw->flags & PVMW_SYNC) && !pvmw->ptl) {
pvmw->ptl = pte_lockptr(mm, pvmw->pmd);
spin_lock(pvmw->ptl);
}
} while (pte_none(*pvmw->pte));
if (!pvmw->ptl) {
pvmw->ptl = pte_lockptr(mm, pvmw->pmd);
spin_lock(pvmw->ptl);
}
goto this_pte;
} while (pvmw->address < end);
return false;
}
/**
* page_mapped_in_vma - check whether a page is really mapped in a VMA
* @page: the page to test
* @vma: the VMA to test
*
* Returns 1 if the page is mapped into the page tables of the VMA, 0
* if the page is not mapped into the page tables of this VMA. Only
* valid for normal file or anonymous VMAs.
*/
int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
{
struct page_vma_mapped_walk pvmw = {
.pfn = page_to_pfn(page),
.nr_pages = 1,
.vma = vma,
.flags = PVMW_SYNC,
};
pvmw.address = vma_address(page, vma);
if (pvmw.address == -EFAULT)
return 0;
if (!page_vma_mapped_walk(&pvmw))
return 0;
page_vma_mapped_walk_done(&pvmw);
return 1;
}
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