Commit-ID: 00e5a2bbcc31d5fea853f8daeba0f06c1c88c3ff Gitweb: https://git.kernel.org/tip/00e5a2bbcc31d5fea853f8daeba0f06c1c88c3ff Author: Baoquan He bhe@redhat.com AuthorDate: Thu, 23 May 2019 10:57:44 +0800 Committer: Borislav Petkov bp@suse.de CommitDate: Fri, 7 Jun 2019 23:12:13 +0200

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 --- 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 dc3f058bdf9b..dc6182eecefa 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 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++)