[PATCH v3 5/6] x86/mm/KASLR: Calculate the actual size of vmemmap region

From: Baoquan He
Date: Sat Feb 16 2019 - 09:04:16 EST


Vmemmap region has different maximum size depending on paging mode.
Now its size is hardcoded as 1TB in memory KASLR, this is not
right for 5-level paging mode. It will cause overflow if vmemmap
region is randomized to be adjacent to cpu_entry_area region and
its actual size is bigger than 1TB.

So here calculate how many TB by the actual size of vmemmap region
and align up to 1TB boundary.

Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
---
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 97768df923e3..ca12ed4e5239 100644
--- a/arch/x86/mm/kaslr.c
+++ b/arch/x86/mm/kaslr.c
@@ -101,7 +101,7 @@ static __initdata struct kaslr_memory_region {
} kaslr_regions[] = {
{ &page_offset_base, 0 },
{ &vmalloc_base, 0 },
- { &vmemmap_base, 1 },
+ { &vmemmap_base, 0 },
};

/*
@@ -121,6 +121,7 @@ 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;
@@ -152,6 +153,14 @@ 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 align 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