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Date: Wed, 8 May 2019 16:04:17 +0800 From: Baoquan He <bhe@...hat.com> To: linux-kernel@...r.kernel.org Cc: x86@...nel.org, tglx@...utronix.de, mingo@...nel.org, bp@...en8.de, hpa@...or.com, kirill.shutemov@...ux.intel.com, keescook@...omium.org, Baoquan He <bhe@...hat.com> Subject: [PATCH v4] x86/mm/KASLR: Fix the size of vmemmap section 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 way, the left space can be saved to join randomization to increase the entropy. Signed-off-by: Baoquan He <bhe@...hat.com> Acked-by: Kirill A. Shutemov <kirill@...ux.intel.com> Reviewed-by: Kees Cook <keescook@...omium.org> --- v3->v4: Fix the incorrect style of code comment; Add ack tags from Kirill and Kees. v3 discussion is here: http://lkml.kernel.org/r/20190422091045.GB3584@localhost.localdomain 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..c0eedb85a92f 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
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