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Kirill A. Shutemov 432c833218 x86/mm: Handle physical-virtual alignment mismatch in phys_p4d_init() 
Kyle has reported occasional crashes when booting a kernel in 5-level
paging mode with KASLR enabled:

  WARNING: CPU: 0 PID: 0 at arch/x86/mm/init_64.c:87 phys_p4d_init+0x1d4/0x1ea
  RIP: 0010:phys_p4d_init+0x1d4/0x1ea
  Call Trace:
   __kernel_physical_mapping_init+0x10a/0x35c
   kernel_physical_mapping_init+0xe/0x10
   init_memory_mapping+0x1aa/0x3b0
   init_range_memory_mapping+0xc8/0x116
   init_mem_mapping+0x225/0x2eb
   setup_arch+0x6ff/0xcf5
   start_kernel+0x64/0x53b
   ? copy_bootdata+0x1f/0xce
   x86_64_start_reservations+0x24/0x26
   x86_64_start_kernel+0x8a/0x8d
   secondary_startup_64+0xb6/0xc0

which causes later:

  BUG: unable to handle page fault for address: ff484d019580eff8
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not-present page
  BAD
  Oops: 0000 [#1] SMP NOPTI
  RIP: 0010:fill_pud+0x13/0x130
  Call Trace:
   set_pte_vaddr_p4d+0x2e/0x50
   set_pte_vaddr+0x6f/0xb0
   __native_set_fixmap+0x28/0x40
   native_set_fixmap+0x39/0x70
   register_lapic_address+0x49/0xb6
   early_acpi_boot_init+0xa5/0xde
   setup_arch+0x944/0xcf5
   start_kernel+0x64/0x53b

Kyle bisected the issue to commit b569c18434 ("x86/mm/KASLR: Reduce
randomization granularity for 5-level paging to 1GB")

Before this commit PAGE_OFFSET was always aligned to P4D_SIZE when booting
5-level paging mode. But now only PUD_SIZE alignment is guaranteed.

In the case I was able to reproduce the following vaddr/paddr values were
observed in phys_p4d_init():

Iteration     vaddr			paddr
   1 	      0xff4228027fe00000 	0x033fe00000
   2	      0xff42287f40000000	0x8000000000

'vaddr' in both cases belongs to the same p4d entry.

But due to the original assumption that PAGE_OFFSET is aligned to P4D_SIZE
this overlap cannot be handled correctly. The code assumes strictly aligned
entries and unconditionally increments the index into the P4D table, which
creates false duplicate entries. Once the index reaches the end, the last
entry in the page table is missing.

Aside of that the 'paddr >= paddr_end' condition can evaluate wrong which
causes an P4D entry to be cleared incorrectly.

Change the loop in phys_p4d_init() to walk purely based on virtual
addresses like __kernel_physical_mapping_init() does. This makes it work
correctly with unaligned virtual addresses.

Fixes: b569c18434 ("x86/mm/KASLR: Reduce randomization granularity for 5-level paging to 1GB")
Reported-by: Kyle Pelton <kyle.d.pelton@intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Kyle Pelton <kyle.d.pelton@intel.com>
Acked-by: Baoquan He <bhe@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20190624123150.920-1-kirill.shutemov@linux.intel.com
2019-06-26 07:25:09 +02:00
arch x86/mm: Handle physical-virtual alignment mismatch in phys_p4d_init() 2019-06-26 07:25:09 +02:00
block block: print offending values when cloned rq limits are exceeded 2019-05-31 15:12:34 -06:00
certs treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 36 2019-05-24 17:27:11 +02:00
crypto treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 174 2019-05-30 11:26:41 -07:00
Documentation mm, memcg: consider subtrees in memory.events 2019-06-01 15:51:31 -07:00
drivers Merge branch 'efi-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-06-02 11:06:13 -07:00
fs for-linus-20190601 2019-06-02 09:27:44 -07:00
include x86/microcode, cpuhotplug: Add a microcode loader CPU hotplug callback 2019-06-15 10:00:29 +02:00
init treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 167 2019-05-30 11:26:39 -07:00
ipc treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 52 2019-05-24 17:36:42 +02:00
kernel Merge branch 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-06-02 11:08:12 -07:00
lib SPDX fixes for 5.2-rc3, round 2 2019-06-02 10:22:38 -07:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
mm mm/vmalloc: Avoid rare case of flushing TLB with weird arguments 2019-06-03 11:47:25 +02:00
net SPDX update for 5.2-rc3, round 1 2019-05-31 08:34:32 -07:00
samples treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 206 2019-05-30 11:29:53 -07:00
scripts Merge branch 'akpm' (patches from Andrew) 2019-06-02 08:51:30 -07:00
security Merge branch 'next-fixes-for-5.2-rc' of git://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-integrity 2019-05-31 11:08:44 -07:00
sound treewide: fix typos of SPDX-License-Identifier 2019-06-01 18:29:58 +02:00
tools Merge branch 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-06-02 11:08:12 -07:00
usr user/Makefile: Fix typo and capitalization in comment section 2018-12-11 00:18:03 +09:00
virt Fixes for PPC and s390. 2019-06-02 10:19:39 -07:00
.clang-format Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-04-17 11:26:25 -07:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore .gitignore: exclude .get_maintainer.ignore and .gitattributes 2019-05-18 11:49:54 +09:00
.mailmap A reasonably busy cycle for docs, including: 2019-05-08 12:42:50 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS MAINTAINERS: Farewell Martin Schwidefsky 2019-05-31 10:14:11 +02:00
Kbuild Kbuild updates for v5.1 2019-03-10 17:48:21 -07:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS Merge branch 'i2c/for-current' of git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux 2019-06-02 10:18:11 -07:00
Makefile Linux 5.2-rc3 2019-06-02 13:55:33 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.