x86/mm/KASLR: Compute the size of the vmemmap section properly

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@redhat.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Kirill A. Shutemov <kirill@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: kirill.shutemov@linux.intel.com
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable <stable@vger.kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20190523025744.3756-1-bhe@redhat.com

diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
index dc3f058..dc6182e 100644 (file)
--- 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 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++)