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Date:   Tue, 25 Jun 2019 22:29:46 -0700
From:   "tip-bot for Kirill A. Shutemov" <>
Subject: [tip:x86/urgent] x86/mm: Handle physical-virtual alignment mismatch
 in phys_p4d_init()

Commit-ID:  432c833218dd0f75e7b56bd5e8658b72073158d2
Author:     Kirill A. Shutemov <>
AuthorDate: Mon, 24 Jun 2019 15:31:50 +0300
Committer:  Thomas Gleixner <>
CommitDate: Wed, 26 Jun 2019 07:25:09 +0200

x86/mm: Handle physical-virtual alignment mismatch in phys_p4d_init()

Kyle has reported occasional crashes when booting a kernel in 5-level
paging mode with KASLR enabled:

  WARNING: CPU: 0 PID: 0 at arch/x86/mm/init_64.c:87 phys_p4d_init+0x1d4/0x1ea
  RIP: 0010:phys_p4d_init+0x1d4/0x1ea
  Call Trace:
   ? copy_bootdata+0x1f/0xce

which causes later:

  BUG: unable to handle page fault for address: ff484d019580eff8
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not-present page
  Oops: 0000 [#1] SMP NOPTI
  RIP: 0010:fill_pud+0x13/0x130
  Call Trace:

Kyle bisected the issue to commit b569c1843498 ("x86/mm/KASLR: Reduce
randomization granularity for 5-level paging to 1GB")

Before this commit PAGE_OFFSET was always aligned to P4D_SIZE when booting
5-level paging mode. But now only PUD_SIZE alignment is guaranteed.

In the case I was able to reproduce the following vaddr/paddr values were
observed in phys_p4d_init():

Iteration     vaddr			paddr
   1 	      0xff4228027fe00000 	0x033fe00000
   2	      0xff42287f40000000	0x8000000000

'vaddr' in both cases belongs to the same p4d entry.

But due to the original assumption that PAGE_OFFSET is aligned to P4D_SIZE
this overlap cannot be handled correctly. The code assumes strictly aligned
entries and unconditionally increments the index into the P4D table, which
creates false duplicate entries. Once the index reaches the end, the last
entry in the page table is missing.

Aside of that the 'paddr >= paddr_end' condition can evaluate wrong which
causes an P4D entry to be cleared incorrectly.

Change the loop in phys_p4d_init() to walk purely based on virtual
addresses like __kernel_physical_mapping_init() does. This makes it work
correctly with unaligned virtual addresses.

Fixes: b569c1843498 ("x86/mm/KASLR: Reduce randomization granularity for 5-level paging to 1GB")
Reported-by: Kyle Pelton <>
Signed-off-by: Kirill A. Shutemov <>
Signed-off-by: Thomas Gleixner <>
Tested-by: Kyle Pelton <>
Acked-by: Baoquan He <>
Cc: Borislav Petkov <>
Cc: "H. Peter Anvin" <>
Cc: Dave Hansen <>
Cc: Andy Lutomirski <>
Cc: Peter Zijlstra <>

 arch/x86/mm/init_64.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 693aaf28d5fe..0f01c7b1d217 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -671,23 +671,25 @@ static unsigned long __meminit
 phys_p4d_init(p4d_t *p4d_page, unsigned long paddr, unsigned long paddr_end,
 	      unsigned long page_size_mask, bool init)
-	unsigned long paddr_next, paddr_last = paddr_end;
-	unsigned long vaddr = (unsigned long)__va(paddr);
-	int i = p4d_index(vaddr);
+	unsigned long vaddr, vaddr_end, vaddr_next, paddr_next, paddr_last;
+	paddr_last = paddr_end;
+	vaddr = (unsigned long)__va(paddr);
+	vaddr_end = (unsigned long)__va(paddr_end);
 	if (!pgtable_l5_enabled())
 		return phys_pud_init((pud_t *) p4d_page, paddr, paddr_end,
 				     page_size_mask, init);
-	for (; i < PTRS_PER_P4D; i++, paddr = paddr_next) {
-		p4d_t *p4d;
+	for (; vaddr < vaddr_end; vaddr = vaddr_next) {
+		p4d_t *p4d = p4d_page + p4d_index(vaddr);
 		pud_t *pud;
-		vaddr = (unsigned long)__va(paddr);
-		p4d = p4d_page + p4d_index(vaddr);
-		paddr_next = (paddr & P4D_MASK) + P4D_SIZE;
+		vaddr_next = (vaddr & P4D_MASK) + P4D_SIZE;
+		paddr = __pa(vaddr);
 		if (paddr >= paddr_end) {
+			paddr_next = __pa(vaddr_next);
 			if (!after_bootmem &&
 			    !e820__mapped_any(paddr & P4D_MASK, paddr_next,
 					     E820_TYPE_RAM) &&
@@ -699,13 +701,13 @@ phys_p4d_init(p4d_t *p4d_page, unsigned long paddr, unsigned long paddr_end,
 		if (!p4d_none(*p4d)) {
 			pud = pud_offset(p4d, 0);
-			paddr_last = phys_pud_init(pud, paddr, paddr_end,
-						   page_size_mask, init);
+			paddr_last = phys_pud_init(pud, paddr, __pa(vaddr_end),
+					page_size_mask, init);
 		pud = alloc_low_page();
-		paddr_last = phys_pud_init(pud, paddr, paddr_end,
+		paddr_last = phys_pud_init(pud, paddr, __pa(vaddr_end),
 					   page_size_mask, init);

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