linux-kernel - [PATCH 5.1 110/115] x86/mm/KASLR: Compute the size of the vmemmap section properly

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Date:   Mon, 17 Jun 2019 23:10:10 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Baoquan He <bhe@...hat.com>,
        Borislav Petkov <bp@...e.de>,
        Kees Cook <keescook@...omium.org>,
        "Kirill A. Shutemov" <kirill@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
        kirill.shutemov@...ux.intel.com,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>, x86-ml <x86@...nel.org>
Subject: [PATCH 5.1 110/115] x86/mm/KASLR: Compute the size of the vmemmap section properly

From: Baoquan He <bhe@...hat.com>

commit 00e5a2bbcc31d5fea853f8daeba0f06c1c88c3ff upstream.

The size of the vmemmap section is hardcoded to 1 TB to support the
maximum amount of system RAM in 4-level paging mode - 64 TB.

However, 1 TB is not enough for vmemmap in 5-level paging mode. Assuming
the size of struct page is 64 Bytes, to support 4 PB system RAM in 5-level,
64 TB of vmemmap area is needed:

  4 * 1000^5 PB / 4096 bytes page size * 64 bytes per page struct / 1000^4 TB = 62.5 TB.

This hardcoding may cause vmemmap to corrupt the following
cpu_entry_area section, if KASLR puts vmemmap very close to it and the
actual vmemmap size is bigger than 1 TB.

So calculate the actual size of the vmemmap region needed and then align
it up to 1 TB boundary.

In 4-level paging mode it is always 1 TB. In 5-level it's adjusted on
demand. The current code reserves 0.5 PB for vmemmap on 5-level. With
this change, the space can be saved and thus used to increase entropy
for the randomization.

 [ bp: Spell out how the 64 TB needed for vmemmap is computed and massage commit
   message. ]

Fixes: eedb92abb9bb ("x86/mm: Make virtual memory layout dynamic for CONFIG_X86_5LEVEL=y")
Signed-off-by: Baoquan He <bhe@...hat.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Kees Cook <keescook@...omium.org>
Acked-by: Kirill A. Shutemov <kirill@...ux.intel.com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: kirill.shutemov@...ux.intel.com
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: stable <stable@...r.kernel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: x86-ml <x86@...nel.org>
Link: https://lkml.kernel.org/r/20190523025744.3756-1-bhe@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/mm/kaslr.c |   11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

--- a/arch/x86/mm/kaslr.c
+++ b/arch/x86/mm/kaslr.c
@@ -52,7 +52,7 @@ static __initdata struct kaslr_memory_re
 } kaslr_regions[] = {
 	{ &page_offset_base, 0 },
 	{ &vmalloc_base, 0 },
-	{ &vmemmap_base, 1 },
+	{ &vmemmap_base, 0 },
 };

 /* Get size in bytes used by the memory region */
@@ -78,6 +78,7 @@ void __init kernel_randomize_memory(void
 	unsigned long rand, memory_tb;
 	struct rnd_state rand_state;
 	unsigned long remain_entropy;
+	unsigned long vmemmap_size;

 	vaddr_start = pgtable_l5_enabled() ? __PAGE_OFFSET_BASE_L5 : __PAGE_OFFSET_BASE_L4;
 	vaddr = vaddr_start;
@@ -109,6 +110,14 @@ void __init kernel_randomize_memory(void
 	if (memory_tb < kaslr_regions[0].size_tb)
 		kaslr_regions[0].size_tb = memory_tb;

+	/*
+	 * Calculate the vmemmap region size in TBs, aligned to a TB
+	 * boundary.
+	 */
+	vmemmap_size = (kaslr_regions[0].size_tb << (TB_SHIFT - PAGE_SHIFT)) *
+			sizeof(struct page);
+	kaslr_regions[2].size_tb = DIV_ROUND_UP(vmemmap_size, 1UL << TB_SHIFT);
+
 	/* Calculate entropy available between regions */
 	remain_entropy = vaddr_end - vaddr_start;
 	for (i = 0; i < ARRAY_SIZE(kaslr_regions); i++)