[kernel/f18] mm: Check if PUD is large when validating a kernel address

Tue Feb 12 16:59:15 UTC 2013

commit e647299c724761a480febdf557b67ad15d607693
Author: Dave Jones <davej at redhat.com>
Date:   Tue Feb 12 11:59:02 2013 -0500

    mm: Check if PUD is large when validating a kernel address

 kernel.spec                  |    7 +++
 validate-pud-largepage.patch |  102 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 109 insertions(+), 0 deletions(-)
---

diff --git a/kernel.spec b/kernel.spec
index 2bcc58a..1bd574b 100644
--- a/kernel.spec
+++ b/kernel.spec
@@ -791,6 +791,8 @@ Patch22247: ath9k_rx_dma_stop_check.patch
 
 Patch23000: silence-brcmsmac-warning.patch
 
+Patch23100: validate-pud-largepage.patch
+
 # END OF PATCH DEFINITIONS
 
 %endif
@@ -1519,6 +1521,8 @@ ApplyPatch ath9k_rx_dma_stop_check.patch
 
 ApplyPatch silence-brcmsmac-warning.patch
 
+ApplyPatch validate-pud-largepage.patch
+
 # END OF PATCH APPLICATIONS
 
 %endif
@@ -2383,6 +2387,9 @@ fi
 #                 ||     ||
 %changelog
 * Tue Feb 12 2013 Dave Jones <davej at redhat.com>
+- mm: Check if PUD is large when validating a kernel address
+
+* Tue Feb 12 2013 Dave Jones <davej at redhat.com>
 - Silence brcmsmac warnings. (Fixed in 3.8, but not backporting to 3.7)
 
 * Tue Feb 12 2013 Justin M. Forbes <jforbes at redhat.com>
diff --git a/validate-pud-largepage.patch b/validate-pud-largepage.patch
new file mode 100644
index 0000000..db67112
--- /dev/null
+++ b/validate-pud-largepage.patch
@@ -0,0 +1,102 @@
+Date: Mon, 11 Feb 2013 14:52:36 +0000
+From: Mel Gorman <mgorman at suse.de>
+To: Ingo Molnar <mingo at kernel.org>, Andrew Morton <akpm at linux-foundation.org>
+Cc: Mel Gorman <mgorman at suse.de>, linux-kernel at vger.kernel.org, linux-mm at kvack.org
+Subject: [PATCH] x86: mm: Check if PUD is large when validating a kernel address
+Message-ID: <20130211145236.GX21389 at suse.de>
+MIME-Version: 1.0
+
+A user reported the following oops when a backup process read
+/proc/kcore.
+
+ 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
+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.
+
+Unfortunately the problem was not readily reproducible and now they are
+running the backup program without accessing /proc/kcore so the patch has
+not been validated but I think it makes sense. If reviewers agree then it
+should also be included in -stable back as far as 3.0-stable.
+
+Cc: stable at vger.kernel.org
+Signed-off-by: Mel Gorman <mgorman at suse.de>
+---
+ 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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