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From: Baoquan He <bhe@redhat.com>
To: linux-kernel@vger.kernel.org
Cc: x86@kernel.org, tglx@linutronix.de, mingo@kernel.org,
	bp@alien8.de, hpa@zytor.com, kirill.shutemov@linux.intel.com,
	keescook@chromium.org, peterz@infradead.org, thgarnie@google.com,
	herbert@gondor.apana.org.au, mike.travis@hpe.com,
	frank.ramsay@hpe.com, yamada.masahiro@socionext.com
Subject: [PATCH v3 RESEND 2/2] x86/mm/KASLR: Fix the size of vmemmap section
Date: Mon, 22 Apr 2019 17:10:45 +0800	[thread overview]
Message-ID: <20190422091045.GB3584@localhost.localdomain> (raw)
In-Reply-To: <20190414072804.12560-3-bhe@redhat.com>

kernel_randomize_memory() hardcodes the size of vmemmap section as 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. The wrong hardcoding may cause vmemmap
stamping into the following cpu_entry_area section, if KASLR puts vmemmap
very close to cpu_entry_area , and the actual area of vmemmap is much bigger
than 1 TB.

So here calculate the actual size of vmemmap region, then align up to 1 TB
boundary. In 4-level it's always 1 TB. In 5-level it's adjusted on demand.
The current code reserves 0.5 PB for vmemmap in 5-level. In this new method,
the left space can be saved to join randomization to increase the entropy.

Signed-off-by: Baoquan He <bhe@redhat.com>
---
v2->v3:
  Fix typo Boris pointed out. 

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

diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
index 387d4ed25d7c..4679a0075048 100644
--- a/arch/x86/mm/kaslr.c
+++ b/arch/x86/mm/kaslr.c
@@ -52,7 +52,7 @@ static __initdata struct kaslr_memory_region {
 } 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 how many TB vmemmap region needs, and aligned to
+	 * 1TB 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++)
-- 
2.17.2


  parent reply	other threads:[~2019-04-22  9:10 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-14  7:28 [PATCH v2 RESEND 0/2] x86/mm/KASLR: Fix the wrong size of memory sections Baoquan He
2019-04-14  7:28 ` [PATCH v2 RESEND 1/2] x86/mm/KASLR: Fix the size of the direct mapping section Baoquan He
2019-04-15 18:53   ` Borislav Petkov
2019-04-17  8:35     ` Baoquan He
2019-04-17 15:01       ` Borislav Petkov
2019-04-17 22:42         ` Baoquan He
2019-04-18  8:52       ` [tip:x86/urgent] " tip-bot for Baoquan He
2019-04-14  7:28 ` [PATCH v2 RESEND 2/2] x86/mm/KASLR: Fix the size of vmemmap section Baoquan He
2019-04-15 19:47   ` Borislav Petkov
2019-04-17  8:39     ` Baoquan He
2019-04-26  9:23     ` Baoquan He
2019-04-26 10:04       ` Borislav Petkov
2019-04-26 10:18         ` Baoquan He
2019-04-22  9:10   ` Baoquan He [this message]
2019-04-22  9:14     ` [PATCH v3 " Baoquan He
2019-04-28 18:54     ` Kirill A. Shutemov
2019-04-29  8:12       ` Baoquan He
2019-04-29 13:16         ` Kirill A. Shutemov

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