[PATCH v2 2/3] x86/mm/KASLR: Calculate the actual size of vmemmap region

[Baoquan He]

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 <b...@redhat.com>
---
 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 0988971069c9..1db8e166455e 100644
--- a/arch/x86/mm/kaslr.c
+++ b/arch/x86/mm/kaslr.c
@@ -51,7 +51,7 @@ 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 */
@@ -77,6 +77,7 @@ 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;
@@ -108,6 +109,14 @@ 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++)
-- 
2.13.6