Date:	Sun, 28 Apr 2013 11:17:46 +0800
From:	Will Huck <will.huckk@...il.com>
To:	Frantisek Hrbata <fhrbata@...hat.com>
CC:	hpa@...or.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	tglx@...utronix.de, mingo@...hat.com, x86@...nel.org,
	oleg@...hat.com, kamaleshb@...ibm.com, hechjie@...ibm.com
Subject: Re: [PATCH] x86: add phys addr validity check for /dev/mem mmap

On 04/28/2013 03:13 AM, Frantisek Hrbata wrote:
> On Sat, Apr 27, 2013 at 03:00:11PM +0800, Will Huck wrote:
>> On 04/26/2013 11:35 PM, Frantisek Hrbata wrote:
>>> On Fri, Apr 26, 2013 at 01:21:28PM +0800, Will Huck wrote:
>>>> Hi Peter,
>>>> On 04/02/2013 08:28 PM, Frantisek Hrbata wrote:
>>>>> When CR4.PAE is set, the 64b PTE's are used(ARCH_PHYS_ADDR_T_64BIT is set for
>>>>> X86_64 || X86_PAE). According to [1] Chapter 4 Paging, some higher bits in 64b
>>>>> PTE are reserved and have to be set to zero. For example, for IA-32e and 4KB
>>>>> page [1] 4.5 IA-32e Paging: Table 4-19, bits 51-M(MAXPHYADDR) are reserved. So
>>>>> for a CPU with e.g. 48bit phys addr width, bits 51-48 have to be zero. If one of
>>>>> the reserved bits is set, [1] 4.7 Page-Fault Exceptions, the #PF is generated
>>>>> with RSVD error code.
>>>>>
>>>>> <quote>
>>>>> RSVD flag (bit 3).
>>>>> This flag is 1 if there is no valid translation for the linear address because a
>>>>> reserved bit was set in one of the paging-structure entries used to translate
>>>>> that address. (Because reserved bits are not checked in a paging-structure entry
>>>>> whose P flag is 0, bit 3 of the error code can be set only if bit 0 is also
>>>>> set.)
>>>>> </quote>
>>>>>
>>>>> In mmap_mem() the first check is valid_mmap_phys_addr_range(), but it always
>>>>> returns 1 on x86. So it's possible to use any pgoff we want and to set the PTE's
>>>>> reserved bits in remap_pfn_range(). Meaning there is a possibility to use mmap
>>>> In this case, remap_pfn_range() setup the map and reserved bits for
>>>> mmio memory, so the mmio memory is already populated, why trigger
>>>> #PF?
>>> Hi,
>>>
>>> I think this is described in the quote above for the RSVD flag.
>>>
>>> remap_pfn_range() => page present => touch page => tlb miss =>
>>> walk through paging structures => reserved bit set => #pf with rsvd flag
>> Page present can also trigger #PF? why?
> Yes, please see
> Intel 64 and IA-32 Architectures Software Developer's Manual, Volume 3A
>
> 4.7 PAGE-FAULT EXCEPTIONS
> <quote>
> · RSVD flag (bit 3).
> This flag is 1 if there is no valid translation for the linear address because
> a reserved bit was set in one of the paging-structure entries used to
> translate that address. (Because reserved bits are not checked in a
> paging-structure entry whose P flag is 0, bit 3 of the error code can be set
> only if bit 0 is also set.) Bits reserved in the paging-structure entries are
> reserved for future functionality. Software developers should be aware that
> such bits may be used in the future and that a paging-structure entry that
> causes a page-fault exception on one processor might not do so in the future.
> </quote>
>
> I cannot tell you why. I guess this is more a question for some Intel guys.
>
> Anyway this patch is trying to fix the following problem and
> the "Bad pagetable" oops.
>
> ---------------------------------8<--------------------------------------
> #include <stdio.h>
> #include <unistd.h>
> #include <sys/types.h>
> #include <sys/stat.h>
> #include <fcntl.h>
> #include <err.h>
> #include <stdlib.h>
> #include <sys/mman.h>
>
> #define die(fmt, ...) err(1, fmt, ##__VA_ARGS__)
>
> /*
>     1) Find some non system ram in case the CONFIG_STRICT_DEVMEM is defined
>     $ cat /proc/iomem | grep -v "\(System RAM\|reserved\)"
>
>     2) Find physical address width
>     $ cat /proc/cpuinfo | grep "address sizes"
>
>     PTE bits 51 - M are reserved, where M is physical address width found 2)
>     Note: step 2) is actually not needed, we can always set just the 51th bit
>     (0x8000000000000)

What's the meaning here? You trigger oops since the address is beyond 
max address cpu supported or access to a reserved page? If the answer is 
the latter, I'm think it's not right. For example, the kernel code/data 
section is reserved in memory, kernel access it will trigger oops? I 
don't think so.

>
>     Set OFFSET macro to
>
>     (start of iomem range found in 1)) | (1 << 51)
>
>     for example
>     0x000a0000 | 0x8000000000000 = 0x80000000a0000
>
>     where 0x000a0000 is start of PCI BUS on my laptop
>
>   */
>
> #define OFFSET 0x80000000a0000LL
>
> int main(int argc, char *argv[])
> {
> 	int fd;
> 	long ps;
> 	long pgoff;
> 	char *map;
> 	char c;
>
> 	ps = sysconf(_SC_PAGE_SIZE);
> 	if (ps == -1)
> 		die("cannot get page size");
>
> 	fd = open("/dev/mem", O_RDONLY);
> 	if (fd == -1)
> 		die("cannot open /dev/mem");
>
> 	printf("%Lx\n", pgoff);
> 	pgoff = (OFFSET + (ps - 1)) & ~(ps - 1);
> 	printf("%Lx\n", pgoff);
>
> 	map = mmap(NULL, ps, PROT_READ, MAP_SHARED, fd, pgoff);
> 	if (map == MAP_FAILED)
> 		die("cannot mmap");
>
> 	c = map[0];
>
> 	if (munmap(map, ps) == -1)
> 		die("cannot munmap");
>
> 	if (close(fd) == -1)
> 		die("cannot close");
>
> 	return 0;
> }
> ---------------------------------8<--------------------------------------
>
> Apr 27 19:52:29 dhcp-26-164 kernel: [ 6464.814860] pfrsvd: Corrupted page table at address 7f34087c8000
> Apr 27 19:52:29 dhcp-26-164 kernel: [ 6464.817356] PGD 12d0b3067 PUD 12d544067 PMD 12e29d067 PTE 80080000000a0225
> Apr 27 19:52:29 dhcp-26-164 kernel: [ 6464.820216] Bad pagetable: 000d [#1] SMP
> Apr 27 19:52:29 dhcp-26-164 kernel: [ 6464.822821] Modules linked in: fuse ebtable_nat xt_CHECKSUM bridge stp llc ipt_MASQUERADE nf_conntrack_netbios_ns nf_conntrack_broadcast ip6table_mangle ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 iptable_nat nf_nat_ipv4 nf_nat iptable_mangle nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack ebtable_filter ebtables ip6table_filter ip6_tables be2iscsi iscsi_boot_sysfs bnx2i cnic uio cxgb4i cxgb4 cxgb3i cxgb3 mdio libcxgbi ib_iser rdma_cm ib_addr iw_cm ib_cm ib_sa ib_mad ib_core iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi rfcomm bnep arc4 iwldvm mac80211 snd_hda_codec_hdmi snd_hda_codec_conexant snd_hda_intel snd_hda_codec uvcvideo snd_hwdep snd_seq snd_seq_device snd_pcm iTCO_wdt videobuf2_vmalloc videobuf2_memops videobuf2_core videodev btusb snd_page_alloc bluetooth snd_timer thinkpad_acpi iwlwifi media snd i2c_i801 cfg80211 iTCO_vendor_support intel_ips e1000e coretemp lpc_ich mfd_core soundcore rfkill mei microcode nfsd auth_rpcgss nfs_acl lockd sunrpc vhost_net tun macvtap macvlan kvm_intel kvm binfmt_misc uinput dm_crypt crc32c_intel i915 ghash_clmulni_intel firewire_ohci i2c_algo_bit drm_kms_helper firewire_core sdhci_pci crc_itu_t drm sdhci mmc_core i2c_core mxm_wmi video wmi
> Apr 27 19:52:29 dhcp-26-164 kernel: [ 6464.845686] CPU 3
> Apr 27 19:52:29 dhcp-26-164 kernel: [ 6464.845709] Pid: 8751, comm: pfrsvd Not tainted 3.8.1-201.fc18.x86_64 #1 LENOVO 4384AV1/4384AV1
> Apr 27 19:52:29 dhcp-26-164 kernel: [ 6464.852876] RIP: 0033:[<00000000004007db>]  [<00000000004007db>] 0x4007da
> Apr 27 19:52:29 dhcp-26-164 kernel: [ 6464.856587] RSP: 002b:00007ffff5c12620  EFLAGS: 00010213
> Apr 27 19:52:29 dhcp-26-164 kernel: [ 6464.860296] RAX: 00007f34087c8000 RBX: 0000000000000000 RCX: 00000030fd4eed6a
> Apr 27 19:52:29 dhcp-26-164 kernel: [ 6464.864061] RDX: 0000000000000001 RSI: 0000000000001000 RDI: 0000000000000000
> Apr 27 19:52:29 dhcp-26-164 kernel: [ 6464.867878] RBP: 00007ffff5c12660 R08: 0000000000000003 R09: 00080000000a0000
> Apr 27 19:52:29 dhcp-26-164 kernel: [ 6464.871706] R10: 0000000000000001 R11: 0000000000000206 R12: 00000000004005f0
> Apr 27 19:52:29 dhcp-26-164 kernel: [ 6464.875566] R13: 00007ffff5c12740 R14: 0000000000000000 R15: 0000000000000000
> Apr 27 19:52:29 dhcp-26-164 kernel: [ 6464.879490] FS:  00007f34087a0740(0000) GS:ffff880137d80000(0000) knlGS:0000000000000000
> Apr 27 19:52:29 dhcp-26-164 kernel: [ 6464.883447] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> Apr 27 19:52:29 dhcp-26-164 kernel: [ 6464.887436] CR2: 00007f34087c8000 CR3: 0000000107509000 CR4: 00000000000007e0
> Apr 27 19:52:29 dhcp-26-164 kernel: [ 6464.891495] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> Apr 27 19:52:29 dhcp-26-164 kernel: [ 6464.895603] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> Apr 27 19:52:29 dhcp-26-164 kernel: [ 6464.899739] Process pfrsvd (pid: 8751, threadinfo ffff880104ea8000, task ffff88012d9e1760)
> Apr 27 19:52:29 dhcp-26-164 kernel: [ 6464.903944]
> Apr 27 19:52:29 dhcp-26-164 kernel: [ 6464.908169] RIP  [<00000000004007db>] 0x4007da
> Apr 27 19:52:29 dhcp-26-164 kernel: [ 6464.912447]  RSP <00007ffff5c12620>
> Apr 27 19:52:29 dhcp-26-164 kernel: [ 6464.943802] ---[ end trace 1113d12a53145197 ]---
>
> Please note the PTE value 80080000000a0225
>
> HTH
>
> Thank you
>>> I hope I didn't misunderstand your question.
>>>
>>> Thanks
>>>
>>>>> on /dev/mem and cause system panic. It's probably not that serious, because
>>>>> access to /dev/mem is limited and the system has to have panic_on_oops set, but
>>>>> still I think we should check this and return error.
>>>>>
>>>>> This patch adds check for x86 when ARCH_PHYS_ADDR_T_64BIT is set, the same way
>>>>> as it is already done in e.g. ioremap. With this fix mmap returns -EINVAL if the
>>>>> requested phys addr is bigger then the supported phys addr width.
>>>>>
>>>>> [1] Intel 64 and IA-32 Architectures Software Developer's Manual, Volume 3A
>>>>>
>>>>> Signed-off-by: Frantisek Hrbata <fhrbata@...hat.com>
>>>>> ---
>>>>>   arch/x86/include/asm/io.h |  4 ++++
>>>>>   arch/x86/mm/mmap.c        | 13 +++++++++++++
>>>>>   2 files changed, 17 insertions(+)
>>>>>
>>>>> diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
>>>>> index d8e8eef..39607c6 100644
>>>>> --- a/arch/x86/include/asm/io.h
>>>>> +++ b/arch/x86/include/asm/io.h
>>>>> @@ -242,6 +242,10 @@ static inline void flush_write_buffers(void)
>>>>>   #endif
>>>>>   }
>>>>> +#define ARCH_HAS_VALID_PHYS_ADDR_RANGE
>>>>> +extern int valid_phys_addr_range(phys_addr_t addr, size_t count);
>>>>> +extern int valid_mmap_phys_addr_range(unsigned long pfn, size_t count);
>>>>> +
>>>>>   #endif /* __KERNEL__ */
>>>>>   extern void native_io_delay(void);
>>>>> diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
>>>>> index 845df68..92ec31c 100644
>>>>> --- a/arch/x86/mm/mmap.c
>>>>> +++ b/arch/x86/mm/mmap.c
>>>>> @@ -31,6 +31,8 @@
>>>>>   #include <linux/sched.h>
>>>>>   #include <asm/elf.h>
>>>>> +#include "physaddr.h"
>>>>> +
>>>>>   struct __read_mostly va_alignment va_align = {
>>>>>   	.flags = -1,
>>>>>   };
>>>>> @@ -122,3 +124,14 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
>>>>>   		mm->unmap_area = arch_unmap_area_topdown;
>>>>>   	}
>>>>>   }
>>>>> +
>>>>> +int valid_phys_addr_range(phys_addr_t addr, size_t count)
>>>>> +{
>>>>> +	return addr + count <= __pa(high_memory);
>>>>> +}
>>>>> +
>>>>> +int valid_mmap_phys_addr_range(unsigned long pfn, size_t count)
>>>>> +{
>>>>> +	resource_size_t addr = (pfn << PAGE_SHIFT) + count;
>>>>> +	return phys_addr_valid(addr);
>>>>> +}
>>>> --
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