linux-kernel - Re: [PATCH] x86: do not overrun page table ranges in gup

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Date:	Tue, 29 Jul 2008 04:26:24 +0400
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Johannes Weiner <hannes@...urebad.de>
Cc:	akpm@...l.org, torvalds@...l.org, npiggin@...e.de,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: do not overrun page table ranges in gup

On Tue, Jul 29, 2008 at 02:00:08AM +0200, Johannes Weiner wrote:
> Alexey Dobriyan <adobriyan@...il.com> writes:
> 
> > On Mon, Jul 28, 2008 at 10:49:47PM +0400, Alexey Dobriyan wrote:
> >> Version: 2.6.26-837b41b5de356aa67abb2cadb5eef3efc7776f91
> >> Core2 Duo, x86_64, 4 GB of RAM.
> >> 
> >> Kernel is "tainted" with ZFS driver, but it can so little, and
> >> probability of screwup is very little too. :-)
> >> 
> >> 
> >> Long LTP session finally ended with
> >> 
> >> BUG: unable to handle kernel paging request at ffff88012b60c000
> >> IP: [<ffffffff80223ff4>] gup_pte_range+0x54/0x120
> >> PGD 202063 PUD a067 PMD 17cedc163 PTE 800000012b60c160
> >> Oops: 0000 [1] PREEMPT SMP DEBUG_PAGEALLOC
> >> CPU 0 
> >> Modules linked in: zfs iptable_raw xt_state iptable_filter ipt_MASQUERADE iptable_nat nf_nat nf_conntrack_ipv4 ip_tables x_tables nf_conntrack_irc nf_conntrack fuse usblp uhci_hcd ehci_hcd usbcore sr_mod cdrom [last unloaded: zfs]
> >> Pid: 16863, comm: vmsplice01 Tainted: G        W 2.6.26-zfs #2
> >> RIP: 0010:[<ffffffff80223ff4>]  [<ffffffff80223ff4>] gup_pte_range+0x54/0x120
> >> RSP: 0018:ffff88012ff57c68  EFLAGS: 00010096
> >> RAX: 0000000000000008 RBX: 00007fff4a800000 RCX: 0000000000000001
> >> RDX: ffffe200040b5f00 RSI: 00007fff4a800310 RDI: ffff88012b60c000
> >> RBP: ffff88012ff57c78 R08: 0000000000000005 R09: ffff88012ff57cec
> >> R10: 0000000000000024 R11: 0000000000000205 R12: ffff88012ff57e58
> >> R13: 00007fff4a807310 R14: 00007fff4a80730f R15: ffff88012ff57e58
> >> FS:  00007fbb4280b6f0(0000) GS:ffffffff805dec40(0000) knlGS:0000000000000000
> >> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >> CR2: ffff88012b60c000 CR3: 000000017e294000 CR4: 00000000000006e0
> >> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> >> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> >> Process vmsplice01 (pid: 16863, threadinfo ffff88012ff56000, task ffff88015f9db360)
> >> Stack:  00007fff4a800000 ffff88010e6cf298 ffff88012ff57d18 ffffffff802243cb
> >>  0000000000000002 ffff88015f9db360 0000000004f23a08 00007fff4a7f7310
> >>  ffff88017d582880 00007fff4a807310 00007fff4a807310 ffff88017e2947f8
> >> Call Trace:
> >>  [<ffffffff802243cb>] get_user_pages_fast+0x1db/0x300
> >>  [<ffffffff802b1bfd>] sys_vmsplice+0x32d/0x420
> >>  [<ffffffff80262acd>] ? unlock_page+0x2d/0x40
> >>  [<ffffffff80275d78>] ? __do_fault+0x1c8/0x450
> >>  [<ffffffff8030e20c>] ? __up_read+0x4c/0xb0
> >>  [<ffffffff802495c6>] ? up_read+0x26/0x30
> >>  [<ffffffff802b0780>] ? spd_release_page+0x0/0x20
> >>  [<ffffffff80463f0d>] ? lockdep_sys_exit_thunk+0x35/0x67
> >>  [<ffffffff8020b65b>] system_call_fastpath+0x16/0x1b
> >
> > Very reproducible and ZFS driver doesn't matter:
> >
> > 	# vmsplice01 from LTP 20080630
> > 	# while true; do ./vmsplice01; done
> 
> I think this is the right fix, but my thinking might be buggy, please
> verify.
> 
> ---
> From: Johannes Weiner <hannes@...urebad.de>
> Subject: x86: do not overrun page table ranges in gup
> 
> Walking the addresses in PAGE_SIZE steps and checking for addr != end
> assumes that the distance between addr and end is a multiple of
> PAGE_SIZE.
> 
> This is not garuanteed, though, if the end of this level walk is not the
> total end (for which we know that the distance to the starting address
> is a multiple of PAGE_SIZE) but that of the range the upper level entry
> maps.

This immediately triggers kernel BUG at arch/x86/mm/gup.c:267!

> --- a/arch/x86/mm/gup.c
> +++ b/arch/x86/mm/gup.c
> @@ -92,7 +92,7 @@ static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
>  		pages[*nr] = page;
>  		(*nr)++;
>  
> -	} while (ptep++, addr += PAGE_SIZE, addr != end);
> +	} while (ptep++, addr += PAGE_SIZE, addr <= end);
>  	pte_unmap(ptep - 1);
>  
>  	return 1;
> @@ -131,7 +131,7 @@ static noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr,
>  		(*nr)++;
>  		page++;
>  		refs++;
> -	} while (addr += PAGE_SIZE, addr != end);
> +	} while (addr += PAGE_SIZE, addr <= end);
>  	get_head_page_multiple(head, refs);
>  
>  	return 1;
> @@ -188,7 +188,7 @@ static noinline int gup_huge_pud(pud_t pud, unsigned long addr,
>  		(*nr)++;
>  		page++;
>  		refs++;
> -	} while (addr += PAGE_SIZE, addr != end);
> +	} while (addr += PAGE_SIZE, addr <= end);
>  	get_head_page_multiple(head, refs);
>  
>  	return 1;

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