blob: f7213d0943b82e73ef0181a72def7c3815ab5c0e [file] [log] [blame]
// SPDX-License-Identifier: GPL-2.0
* This code is used on x86_64 to create page table identity mappings on
* demand by building up a new set of page tables (or appending to the
* existing ones), and then switching over to them when ready.
* Copyright (C) 2015-2016 Yinghai Lu
* Copyright (C) 2016 Kees Cook
* Since we're dealing with identity mappings, physical and virtual
* addresses are the same, so override these defines which are ultimately
* used by the headers in misc.h.
#define __pa(x) ((unsigned long)(x))
#define __va(x) ((void *)((unsigned long)(x)))
/* No PAGE_TABLE_ISOLATION support needed either: */
#include "error.h"
#include "misc.h"
/* These actually do the work of building the kernel identity maps. */
#include <linux/pgtable.h>
#include <asm/cmpxchg.h>
#include <asm/trap_pf.h>
#include <asm/trapnr.h>
#include <asm/init.h>
/* Use the static base for this part of the boot process */
#undef __PAGE_OFFSET
#include "../../mm/ident_map.c"
#define _SETUP
#include <asm/setup.h> /* For COMMAND_LINE_SIZE */
#undef _SETUP
extern unsigned long get_cmd_line_ptr(void);
/* Used by PAGE_KERN* macros: */
pteval_t __default_kernel_pte_mask __read_mostly = ~0;
/* Used to track our page table allocation area. */
struct alloc_pgt_data {
unsigned char *pgt_buf;
unsigned long pgt_buf_size;
unsigned long pgt_buf_offset;
* Allocates space for a page table entry, using struct alloc_pgt_data
* above. Besides the local callers, this is used as the allocation
* callback in mapping_info below.
static void *alloc_pgt_page(void *context)
struct alloc_pgt_data *pages = (struct alloc_pgt_data *)context;
unsigned char *entry;
/* Validate there is space available for a new page. */
if (pages->pgt_buf_offset >= pages->pgt_buf_size) {
debug_putstr("out of pgt_buf in " __FILE__ "!?\n");
return NULL;
entry = pages->pgt_buf + pages->pgt_buf_offset;
pages->pgt_buf_offset += PAGE_SIZE;
return entry;
/* Used to track our allocated page tables. */
static struct alloc_pgt_data pgt_data;
/* The top level page table entry pointer. */
static unsigned long top_level_pgt;
phys_addr_t physical_mask = (1ULL << __PHYSICAL_MASK_SHIFT) - 1;
* Mapping information structure passed to kernel_ident_mapping_init().
* Due to relocation, pointers must be assigned at run time not build time.
static struct x86_mapping_info mapping_info;
* Adds the specified range to the identity mappings.
static void add_identity_map(unsigned long start, unsigned long end)
int ret;
/* Align boundary to 2M. */
start = round_down(start, PMD_SIZE);
end = round_up(end, PMD_SIZE);
if (start >= end)
/* Build the mapping. */
ret = kernel_ident_mapping_init(&mapping_info, (pgd_t *)top_level_pgt, start, end);
if (ret)
error("Error: kernel_ident_mapping_init() failed\n");
/* Locates and clears a region for a new top level page table. */
void initialize_identity_maps(void *rmode)
unsigned long cmdline;
/* Exclude the encryption mask from __PHYSICAL_MASK */
physical_mask &= ~sme_me_mask;
/* Init mapping_info with run-time function/buffer pointers. */
mapping_info.alloc_pgt_page = alloc_pgt_page;
mapping_info.context = &pgt_data;
mapping_info.page_flag = __PAGE_KERNEL_LARGE_EXEC | sme_me_mask;
mapping_info.kernpg_flag = _KERNPG_TABLE;
* It should be impossible for this not to already be true,
* but since calling this a second time would rewind the other
* counters, let's just make sure this is reset too.
pgt_data.pgt_buf_offset = 0;
* If we came here via startup_32(), cr3 will be _pgtable already
* and we must append to the existing area instead of entirely
* overwriting it.
* With 5-level paging, we use '_pgtable' to allocate the p4d page table,
* the top-level page table is allocated separately.
* p4d_offset(top_level_pgt, 0) would cover both the 4- and 5-level
* cases. On 4-level paging it's equal to 'top_level_pgt'.
top_level_pgt = read_cr3_pa();
if (p4d_offset((pgd_t *)top_level_pgt, 0) == (p4d_t *)_pgtable) {
pgt_data.pgt_buf = _pgtable + BOOT_INIT_PGT_SIZE;
pgt_data.pgt_buf_size = BOOT_PGT_SIZE - BOOT_INIT_PGT_SIZE;
memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
} else {
pgt_data.pgt_buf = _pgtable;
pgt_data.pgt_buf_size = BOOT_PGT_SIZE;
memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
top_level_pgt = (unsigned long)alloc_pgt_page(&pgt_data);
* New page-table is set up - map the kernel image, boot_params and the
* command line. The uncompressed kernel requires boot_params and the
* command line to be mapped in the identity mapping. Map them
* explicitly here in case the compressed kernel does not touch them,
* or does not touch all the pages covering them.
add_identity_map((unsigned long)_head, (unsigned long)_end);
boot_params = rmode;
add_identity_map((unsigned long)boot_params, (unsigned long)(boot_params + 1));
cmdline = get_cmd_line_ptr();
add_identity_map(cmdline, cmdline + COMMAND_LINE_SIZE);
/* Load the new page-table. */
static pte_t *split_large_pmd(struct x86_mapping_info *info,
pmd_t *pmdp, unsigned long __address)
unsigned long page_flags;
unsigned long address;
pte_t *pte;
pmd_t pmd;
int i;
pte = (pte_t *)info->alloc_pgt_page(info->context);
if (!pte)
return NULL;
address = __address & PMD_MASK;
/* No large page - clear PSE flag */
page_flags = info->page_flag & ~_PAGE_PSE;
/* Populate the PTEs */
for (i = 0; i < PTRS_PER_PMD; i++) {
set_pte(&pte[i], __pte(address | page_flags));
address += PAGE_SIZE;
* Ideally we need to clear the large PMD first and do a TLB
* flush before we write the new PMD. But the 2M range of the
* PMD might contain the code we execute and/or the stack
* we are on, so we can't do that. But that should be safe here
* because we are going from large to small mappings and we are
* also the only user of the page-table, so there is no chance
* of a TLB multihit.
pmd = __pmd((unsigned long)pte | info->kernpg_flag);
set_pmd(pmdp, pmd);
/* Flush TLB to establish the new PMD */
return pte + pte_index(__address);
static void clflush_page(unsigned long address)
unsigned int flush_size;
char *cl, *start, *end;
* Hardcode cl-size to 64 - CPUID can't be used here because that might
* cause another #VC exception and the GHCB is not ready to use yet.
flush_size = 64;
start = (char *)(address & PAGE_MASK);
end = start + PAGE_SIZE;
* First make sure there are no pending writes on the cache-lines to
* flush.
asm volatile("mfence" : : : "memory");
for (cl = start; cl != end; cl += flush_size)
static int set_clr_page_flags(struct x86_mapping_info *info,
unsigned long address,
pteval_t set, pteval_t clr)
pgd_t *pgdp = (pgd_t *)top_level_pgt;
p4d_t *p4dp;
pud_t *pudp;
pmd_t *pmdp;
pte_t *ptep, pte;
* First make sure there is a PMD mapping for 'address'.
* It should already exist, but keep things generic.
* To map the page just read from it and fault it in if there is no
* mapping yet. add_identity_map() can't be called here because that
* would unconditionally map the address on PMD level, destroying any
* PTE-level mappings that might already exist. Use assembly here so
* the access won't be optimized away.
asm volatile("mov %[address], %%r9"
:: [address] "g" (*(unsigned long *)address)
: "r9", "memory");
* The page is mapped at least with PMD size - so skip checks and walk
* directly to the PMD.
p4dp = p4d_offset(pgdp, address);
pudp = pud_offset(p4dp, address);
pmdp = pmd_offset(pudp, address);
if (pmd_large(*pmdp))
ptep = split_large_pmd(info, pmdp, address);
ptep = pte_offset_kernel(pmdp, address);
if (!ptep)
return -ENOMEM;
* Changing encryption attributes of a page requires to flush it from
* the caches.
if ((set | clr) & _PAGE_ENC)
/* Update PTE */
pte = *ptep;
pte = pte_set_flags(pte, set);
pte = pte_clear_flags(pte, clr);
set_pte(ptep, pte);
/* Flush TLB after changing encryption attribute */
return 0;
int set_page_decrypted(unsigned long address)
return set_clr_page_flags(&mapping_info, address, 0, _PAGE_ENC);
int set_page_encrypted(unsigned long address)
return set_clr_page_flags(&mapping_info, address, _PAGE_ENC, 0);
int set_page_non_present(unsigned long address)
return set_clr_page_flags(&mapping_info, address, 0, _PAGE_PRESENT);
static void do_pf_error(const char *msg, unsigned long error_code,
unsigned long address, unsigned long ip)
error_putstr("\nError Code: ");
error_putstr("\nCR2: 0x");
error_putstr("\nRIP relative to _head: 0x");
error_puthex(ip - (unsigned long)_head);
void do_boot_page_fault(struct pt_regs *regs, unsigned long error_code)
unsigned long address = native_read_cr2();
unsigned long end;
bool ghcb_fault;
ghcb_fault = sev_es_check_ghcb_fault(address);
address &= PMD_MASK;
end = address + PMD_SIZE;
* Check for unexpected error codes. Unexpected are:
* - Faults on present pages
* - User faults
* - Reserved bits set
if (error_code & (X86_PF_PROT | X86_PF_USER | X86_PF_RSVD))
do_pf_error("Unexpected page-fault:", error_code, address, regs->ip);
else if (ghcb_fault)
do_pf_error("Page-fault on GHCB page:", error_code, address, regs->ip);
* Error code is sane - now identity map the 2M region around
* the faulting address.
add_identity_map(address, end);