Re: [PATCH] x86: mm: Check if PUD is large when validating a kerneladdress v2

[Simon Jeons]

On 02/13/2013 07:02 PM, Mel Gorman wrote:
> Andrew or Ingo, please pick up.
>
> Changelog since v1
>    o Add reviewed-bys and acked-bys
>
> A user reported a bug whereby a backup process accessing /proc/kcore
> caused an oops.
>
>   BUG: unable to handle kernel paging request at ffffbb00ff33b000
>   IP: [<ffffffff8103157e>] kern_addr_valid+0xbe/0x110
>   PGD 0
>   Oops: 0000 [#1] SMP
>   CPU 6
>   Modules linked in: af_packet nfs lockd fscache auth_rpcgss nfs_acl sunrpc 8021q garp stp llc cpufreq_conservative cpufreq_userspace cpufreq_powersave acpi_cpufreq mperf microcode fuse nls_iso8859_1 nls_cp437 vfat fat loop dm_mod ioatdma ipv6 ipv6_lib igb dca i7core_edac edac_core i2c_i801 i2c_core cdc_ether usbnet bnx2 mii iTCO_wdt iTCO_vendor_support shpchp rtc_cmos pci_hotplug tpm_tis sg tpm pcspkr tpm_bios serio_raw button ext3 jbd mbcache uhci_hcd ehci_hcd usbcore sd_mod crc_t10dif usb_common processor thermal_sys hwmon scsi_dh_emc scsi_dh_rdac scsi_dh_alua scsi_dh_hp_sw scsi_dh ata_generic ata_piix libata megaraid_sas scsi_mod
>
>   Pid: 16196, comm: Hibackp Not tainted 3.0.13-0.27-default #1 IBM System x3550 M3 -[7944 K3G]-/94Y7614
>   RIP: 0010:[<ffffffff8103157e>]  [<ffffffff8103157e>] kern_addr_valid+0xbe/0x110
>   RSP: 0018:ffff88094165fe80  EFLAGS: 00010246
>   RAX: 00003300ff33b000 RBX: ffff880100000000 RCX: 0000000000000000
>   RDX: 0000000100000000 RSI: ffff880000000000 RDI: ff32b300ff33b400
>   RBP: 0000000000001000 R08: 00003ffffffff000 R09: 0000000000000000
>   R10: 22302e31223d6e6f R11: 0000000000000246 R12: 0000000000001000
>   R13: 0000000000003000 R14: 0000000000571be0 R15: ffff88094165ff50
>   FS:  00007ff152d33700(0000) GS:ffff88097f2c0000(0000) knlGS:0000000000000000
>   CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>   CR2: ffffbb00ff33b000 CR3: 00000009405a3000 CR4: 00000000000006e0
>   DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>   DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
>   Process Hibackp (pid: 16196, threadinfo ffff88094165e000, task ffff8808eb9ba600)
>   Stack:
>    ffffffff811b8aaa 0000000000004000 ffff880943fea480 ffff8808ef2bae50
>    ffff880943d32980 fffffffffffffffb ffff8808ef2bae40 ffff88094165ff50
>    0000000000004000 000000000056ebe0 ffffffff811ad847 000000000056ebe0
>   Call Trace:
>    [<ffffffff811b8aaa>] read_kcore+0x17a/0x370
>    [<ffffffff811ad847>] proc_reg_read+0x77/0xc0
>    [<ffffffff81151687>] vfs_read+0xc7/0x130
>    [<ffffffff811517f3>] sys_read+0x53/0xa0
>    [<ffffffff81449692>] system_call_fastpath+0x16/0x1b
>
> Investigation determined that the bug triggered when reading system RAM
> at the 4G mark. On this system, that was the first address using 1G pages

Do you mean there is one page which is 1G?

> for the virt->phys direct mapping so the PUD is pointing to a physical
> address, not a PMD page.  The problem is that the page table walker in
> kern_addr_valid() is not checking pud_large() and treats the physical
> address as if it was a PMD.  If it happens to look like pmd_none then it'll
> silently fail, probably returning zeros instead of real data. If the data
> happens to look like a present PMD though, it will be walked resulting in
> the oops above. This patch adds the necessary pud_large() check.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
> Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>
> Reviewed-by: Michal Hocko <mhocko@xxxxxxx>
> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> ---
>   arch/x86/include/asm/pgtable.h |    5 +++++
>   arch/x86/mm/init_64.c          |    3 +++
>   2 files changed, 8 insertions(+)
>
> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
> index 5199db2..1c1a955 100644
> --- a/arch/x86/include/asm/pgtable.h
> +++ b/arch/x86/include/asm/pgtable.h
> @@ -142,6 +142,11 @@ static inline unsigned long pmd_pfn(pmd_t pmd)
>   	return (pmd_val(pmd) & PTE_PFN_MASK) >> PAGE_SHIFT;
>   }
>   
> +static inline unsigned long pud_pfn(pud_t pud)
> +{
> +	return (pud_val(pud) & PTE_PFN_MASK) >> PAGE_SHIFT;
> +}
> +
>   #define pte_page(pte)	pfn_to_page(pte_pfn(pte))
>   
>   static inline int pmd_large(pmd_t pte)
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 2ead3c8..75c9a6a 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -831,6 +831,9 @@ int kern_addr_valid(unsigned long addr)
>   	if (pud_none(*pud))
>   		return 0;
>   
> +	if (pud_large(*pud))
> +		return pfn_valid(pud_pfn(*pud));
> +
>   	pmd = pmd_offset(pud, addr);
>   	if (pmd_none(*pmd))
>   		return 0;
>
> --
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