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Date: Sun, 28 May 2017 02:45:59 -0700
From: tip-bot for Baoquan He <tipbot@...or.com>
To: linux-tip-commits@...r.kernel.org
Cc: tglx@...utronix.de, keescook@...omium.org, peterz@...radead.org,
bp@...en8.de, mingo@...nel.org, frank.ramsay@....com,
dyoung@...hat.com, bhsharma@...hat.com,
linux-kernel@...r.kernel.org, matt@...eblueprint.co.uk,
bhe@...hat.com, ard.biesheuvel@...aro.org,
torvalds@...ux-foundation.org, rja@....com, thgarnie@...gle.com,
hpa@...or.com
Subject: [tip:efi/urgent] x86/efi: Correct EFI identity mapping under
'efi=old_map' when KASLR is enabled
Commit-ID: 94133e46a0f5ca3f138479806104ab4a8cb0455e
Gitweb: http://git.kernel.org/tip/94133e46a0f5ca3f138479806104ab4a8cb0455e
Author: Baoquan He <bhe@...hat.com>
AuthorDate: Fri, 26 May 2017 12:36:50 +0100
Committer: Ingo Molnar <mingo@...nel.org>
CommitDate: Sun, 28 May 2017 11:06:16 +0200
x86/efi: Correct EFI identity mapping under 'efi=old_map' when KASLR is enabled
For EFI with the 'efi=old_map' kernel option specified, the kernel will panic
when KASLR is enabled:
BUG: unable to handle kernel paging request at 000000007febd57e
IP: 0x7febd57e
PGD 1025a067
PUD 0
Oops: 0010 [#1] SMP
Call Trace:
efi_enter_virtual_mode()
start_kernel()
x86_64_start_reservations()
x86_64_start_kernel()
start_cpu()
The root cause is that the identity mapping is not built correctly
in the 'efi=old_map' case.
On 'nokaslr' kernels, PAGE_OFFSET is 0xffff880000000000 which is PGDIR_SIZE
aligned. We can borrow the PUD table from the direct mappings safely. Given a
physical address X, we have pud_index(X) == pud_index(__va(X)).
However, on KASLR kernels, PAGE_OFFSET is PUD_SIZE aligned. For a given physical
address X, pud_index(X) != pud_index(__va(X)). We can't just copy the PGD entry
from direct mapping to build identity mapping, instead we need to copy the
PUD entries one by one from the direct mapping.
Fix it.
Signed-off-by: Baoquan He <bhe@...hat.com>
Signed-off-by: Matt Fleming <matt@...eblueprint.co.uk>
Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: Bhupesh Sharma <bhsharma@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Young <dyoung@...hat.com>
Cc: Frank Ramsay <frank.ramsay@....com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Russ Anderson <rja@....com>
Cc: Thomas Garnier <thgarnie@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: linux-efi@...r.kernel.org
Link: http://lkml.kernel.org/r/20170526113652.21339-5-matt@codeblueprint.co.uk
[ Fixed and reworded the changelog and code comments to be more readable. ]
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
arch/x86/platform/efi/efi_64.c | 79 +++++++++++++++++++++++++++++++++++++-----
1 file changed, 71 insertions(+), 8 deletions(-)
diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index c488625..eb8dff1 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -71,11 +71,13 @@ static void __init early_code_mapping_set_exec(int executable)
pgd_t * __init efi_call_phys_prolog(void)
{
- unsigned long vaddress;
- pgd_t *save_pgd;
+ unsigned long vaddr, addr_pgd, addr_p4d, addr_pud;
+ pgd_t *save_pgd, *pgd_k, *pgd_efi;
+ p4d_t *p4d, *p4d_k, *p4d_efi;
+ pud_t *pud;
int pgd;
- int n_pgds;
+ int n_pgds, i, j;
if (!efi_enabled(EFI_OLD_MEMMAP)) {
save_pgd = (pgd_t *)read_cr3();
@@ -88,10 +90,49 @@ pgd_t * __init efi_call_phys_prolog(void)
n_pgds = DIV_ROUND_UP((max_pfn << PAGE_SHIFT), PGDIR_SIZE);
save_pgd = kmalloc_array(n_pgds, sizeof(*save_pgd), GFP_KERNEL);
+ /*
+ * Build 1:1 identity mapping for efi=old_map usage. Note that
+ * PAGE_OFFSET is PGDIR_SIZE aligned when KASLR is disabled, while
+ * it is PUD_SIZE ALIGNED with KASLR enabled. So for a given physical
+ * address X, the pud_index(X) != pud_index(__va(X)), we can only copy
+ * PUD entry of __va(X) to fill in pud entry of X to build 1:1 mapping.
+ * This means here we can only reuse the PMD tables of the direct mapping.
+ */
for (pgd = 0; pgd < n_pgds; pgd++) {
- save_pgd[pgd] = *pgd_offset_k(pgd * PGDIR_SIZE);
- vaddress = (unsigned long)__va(pgd * PGDIR_SIZE);
- set_pgd(pgd_offset_k(pgd * PGDIR_SIZE), *pgd_offset_k(vaddress));
+ addr_pgd = (unsigned long)(pgd * PGDIR_SIZE);
+ vaddr = (unsigned long)__va(pgd * PGDIR_SIZE);
+ pgd_efi = pgd_offset_k(addr_pgd);
+ save_pgd[pgd] = *pgd_efi;
+
+ p4d = p4d_alloc(&init_mm, pgd_efi, addr_pgd);
+ if (!p4d) {
+ pr_err("Failed to allocate p4d table!\n");
+ goto out;
+ }
+
+ for (i = 0; i < PTRS_PER_P4D; i++) {
+ addr_p4d = addr_pgd + i * P4D_SIZE;
+ p4d_efi = p4d + p4d_index(addr_p4d);
+
+ pud = pud_alloc(&init_mm, p4d_efi, addr_p4d);
+ if (!pud) {
+ pr_err("Failed to allocate pud table!\n");
+ goto out;
+ }
+
+ for (j = 0; j < PTRS_PER_PUD; j++) {
+ addr_pud = addr_p4d + j * PUD_SIZE;
+
+ if (addr_pud > (max_pfn << PAGE_SHIFT))
+ break;
+
+ vaddr = (unsigned long)__va(addr_pud);
+
+ pgd_k = pgd_offset_k(vaddr);
+ p4d_k = p4d_offset(pgd_k, vaddr);
+ pud[j] = *pud_offset(p4d_k, vaddr);
+ }
+ }
}
out:
__flush_tlb_all();
@@ -104,8 +145,11 @@ void __init efi_call_phys_epilog(pgd_t *save_pgd)
/*
* After the lock is released, the original page table is restored.
*/
- int pgd_idx;
+ int pgd_idx, i;
int nr_pgds;
+ pgd_t *pgd;
+ p4d_t *p4d;
+ pud_t *pud;
if (!efi_enabled(EFI_OLD_MEMMAP)) {
write_cr3((unsigned long)save_pgd);
@@ -115,9 +159,28 @@ void __init efi_call_phys_epilog(pgd_t *save_pgd)
nr_pgds = DIV_ROUND_UP((max_pfn << PAGE_SHIFT) , PGDIR_SIZE);
- for (pgd_idx = 0; pgd_idx < nr_pgds; pgd_idx++)
+ for (pgd_idx = 0; pgd_idx < nr_pgds; pgd_idx++) {
+ pgd = pgd_offset_k(pgd_idx * PGDIR_SIZE);
set_pgd(pgd_offset_k(pgd_idx * PGDIR_SIZE), save_pgd[pgd_idx]);
+ if (!(pgd_val(*pgd) & _PAGE_PRESENT))
+ continue;
+
+ for (i = 0; i < PTRS_PER_P4D; i++) {
+ p4d = p4d_offset(pgd,
+ pgd_idx * PGDIR_SIZE + i * P4D_SIZE);
+
+ if (!(p4d_val(*p4d) & _PAGE_PRESENT))
+ continue;
+
+ pud = (pud_t *)p4d_page_vaddr(*p4d);
+ pud_free(&init_mm, pud);
+ }
+
+ p4d = (p4d_t *)pgd_page_vaddr(*pgd);
+ p4d_free(&init_mm, p4d);
+ }
+
kfree(save_pgd);
__flush_tlb_all();
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