From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f198.google.com (mail-wr0-f198.google.com [209.85.128.198]) by kanga.kvack.org (Postfix) with ESMTP id 46F0F6B026C for ; Wed, 15 Nov 2017 09:13:30 -0500 (EST) Received: by mail-wr0-f198.google.com with SMTP id n37so12745190wrb.17 for ; Wed, 15 Nov 2017 06:13:30 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id s7sor12255529edi.48.2017.11.15.06.13.28 for (Google Transport Security); Wed, 15 Nov 2017 06:13:28 -0800 (PST) Date: Wed, 15 Nov 2017 17:13:27 +0300 From: "Kirill A. Shutemov" Subject: Re: [PATCHv2 1/2] x86/mm: Do not allow non-MAP_FIXED mapping across DEFAULT_MAP_WINDOW border Message-ID: <20171115141326.xzsbkycdwq4vafxf@node.shutemov.name> References: <20171114134322.40321-1-kirill.shutemov@linux.intel.com> <20171114202102.crpgiwgv2lu5aboq@node.shutemov.name> <20171114222718.76w4lmclf6wasbl3@node.shutemov.name> <20171115112702.e2m66wons37imtcj@node.shutemov.name> <20171115121042.dt2us5fsuqmepx4i@node.shutemov.name> <20171115140426.bgvcd3bmegqadm5q@node.shutemov.name> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171115140426.bgvcd3bmegqadm5q@node.shutemov.name> Sender: owner-linux-mm@kvack.org List-ID: To: Thomas Gleixner Cc: "Kirill A. Shutemov" , Ingo Molnar , x86@kernel.org, "H. Peter Anvin" , Linus Torvalds , Andy Lutomirski , Nicholas Piggin , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Wed, Nov 15, 2017 at 05:04:26PM +0300, Kirill A. Shutemov wrote: > On Wed, Nov 15, 2017 at 03:10:42PM +0300, Kirill A. Shutemov wrote: > > On Wed, Nov 15, 2017 at 12:39:40PM +0100, Thomas Gleixner wrote: > > > On Wed, 15 Nov 2017, Kirill A. Shutemov wrote: > > > > On Wed, Nov 15, 2017 at 12:00:46AM +0100, Thomas Gleixner wrote: > > > > > On Wed, 15 Nov 2017, Kirill A. Shutemov wrote: > > > > > > On Tue, Nov 14, 2017 at 09:54:52PM +0100, Thomas Gleixner wrote: > > > > > > > On Tue, 14 Nov 2017, Kirill A. Shutemov wrote: > > > > > > > > > > > > > > > On Tue, Nov 14, 2017 at 05:01:50PM +0100, Thomas Gleixner wrote: > > > > > > > > > @@ -198,11 +199,14 @@ arch_get_unmapped_area_topdown(struct fi > > > > > > > > > /* requesting a specific address */ > > > > > > > > > if (addr) { > > > > > > > > > addr = PAGE_ALIGN(addr); > > > > > > > > > + if (!mmap_address_hint_valid(addr, len)) > > > > > > > > > + goto get_unmapped_area; > > > > > > > > > + > > > > > > > > > > > > > > > > Here and in hugetlb_get_unmapped_area(), we should align the addr after > > > > > > > > the check, not before. Otherwise the alignment itself can bring us over > > > > > > > > the borderline as we align up. > > > > > > > > > > > > > > Hmm, then I wonder whether the next check against vm_start_gap() which > > > > > > > checks against the aligned address is correct: > > > > > > > > > > > > > > addr = PAGE_ALIGN(addr); > > > > > > > vma = find_vma(mm, addr); > > > > > > > > > > > > > > if (end - len >= addr && > > > > > > > (!vma || addr + len <= vm_start_gap(vma))) > > > > > > > return addr; > > > > > > > > > > > > I think the check is correct. The check is against resulting addresses > > > > > > that end up in vm_start/vm_end. In our case we want to figure out what > > > > > > user asked for. > > > > > > > > > > Well, but then checking just against the user supplied addr is only half of > > > > > the story. > > > > > > > > > > addr = boundary - PAGE_SIZE - PAGE_SIZE / 2; > > > > > len = PAGE_SIZE - PAGE_SIZE / 2; > > > > > > > > > > That fits, but then after alignment we end up with > > > > > > > > > > addr = boudary - PAGE_SIZE; > > > > > > > > > > and due to len > PAGE_SIZE this will result in a mapping which crosses the > > > > > boundary, right? So checking against the PAGE_ALIGN(addr) should be the > > > > > right thing to do. > > > > > > > > IIUC, this is only the case if 'len' is not aligned, right? > > > > > > > > >From what I see we expect caller to align it (and mm/mmap.c does this, I > > > > haven't checked other callers). > > > > > > > > And hugetlb would actively reject non-aligned len. > > > > > > > > I *think* we should be fine with checking unaligned 'addr'. > > > > > > I think we should keep it consistent for the normal and the huge case and > > > just check aligned and be done with it. > > > > Aligned 'addr'? Or 'len'? Both? > > > > We would have problem with checking aligned addr. I steped it in hugetlb > > case: > > > > - User asks for mmap((1UL << 47) - PAGE_SIZE, 2 << 20, MAP_HUGETLB); > > > > - On 4-level paging machine this gives us invalid hint address as > > 'TASK_SIZE - len' is more than 'addr'. Goto get_unmapped_area. > > > > - On 5-level paging machine hint address gets rounded up to next 2MB > > boundary that is exactly 1UL << 47 and we happily allocate from full > > address space which may lead to trouble. > > Below is updated patch with self-test. > > Output on 5-level paging machine: > > mmap(NULL): 0x7fbbad1f3000 - OK > mmap(LOW_ADDR): 0x40000000 - OK > mmap(HIGH_ADDR): 0x4000000000000 - OK > mmap(HIGH_ADDR) again: 0xffffbbad1fb000 - OK > mmap(HIGH_ADDR, MAP_FIXED): 0x4000000000000 - OK > mmap(-1): 0xffffbbad1f9000 - OK > mmap(-1) again: 0xffffbbad1f7000 - OK > mmap((1UL << 47), 2 * PAGE_SIZE): 0x7fbbad1f3000 - OK > mmap((1UL << 47), 2 * PAGE_SIZE / 2): 0x7fbbad1f1000 - OK > mmap((1UL << 47) - PAGE_SIZE, 2 * PAGE_SIZE, MAP_FIXED): 0x7ffffffff000 - OK > mmap(NULL, MAP_HUGETLB): 0x7fbbac400000 - OK > mmap(LOW_ADDR, MAP_HUGETLB): 0x40000000 - OK > mmap(HIGH_ADDR, MAP_HUGETLB): 0x4000000000000 - OK > mmap(HIGH_ADDR, MAP_HUGETLB) again: 0xffffbbace00000 - OK > mmap(HIGH_ADDR, MAP_FIXED | MAP_HUGETLB): 0x4000000000000 - OK > mmap(-1, MAP_HUGETLB): (nil) - OK > mmap(-1, MAP_HUGETLB) again: 0x7fbbac400000 - OK > mmap((1UL << 47), 2UL << 20, MAP_HUGETLB): 0x800000000000 - FAILED > mmap((1UL << 47) - (2UL << 20), 4UL << 20, MAP_FIXED | MAP_HUGETLB): 0x7fffffe00000 - OK > > So, only hugetlb is problematic. mmap() aligns addr to PAGE_SIZE. > See round_hint_to_min(). In this case we round address *down* and it works > fine. > > Replacing 'addr = ALIGN(addr, huge_page_size(h))' in hugetlbpage.c with > 'addr &= huge_page_mask(h)' fixes the issue. What about this fixup: diff --git a/arch/x86/kernel/sys_x86_64.c b/arch/x86/kernel/sys_x86_64.c index 835b78720ca2..676774b9bb8d 100644 --- a/arch/x86/kernel/sys_x86_64.c +++ b/arch/x86/kernel/sys_x86_64.c @@ -198,7 +198,7 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0, /* requesting a specific address */ if (addr) { - addr = PAGE_ALIGN(addr); + addr &= PAGE_MASK; if (!mmap_address_hint_valid(addr, len)) goto get_unmapped_area; diff --git a/arch/x86/mm/hugetlbpage.c b/arch/x86/mm/hugetlbpage.c index 92db903c3dad..00b296617ca4 100644 --- a/arch/x86/mm/hugetlbpage.c +++ b/arch/x86/mm/hugetlbpage.c @@ -166,7 +166,7 @@ hugetlb_get_unmapped_area(struct file *file, unsigned long addr, } if (addr) { - addr = ALIGN(addr, huge_page_size(h)); + addr &= huge_page_mask(h); if (!mmap_address_hint_valid(addr, len)) goto get_unmapped_area; -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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