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Joerg Roedel 4819e15f74 x86/mm/32: Bring back vmalloc faulting on x86_32 
One can not simply remove vmalloc faulting on x86-32. Upstream

	commit: 7f0a002b5a ("x86/mm: remove vmalloc faulting")

removed it on x86 alltogether because previously the
arch_sync_kernel_mappings() interface was introduced. This interface
added synchronization of vmalloc/ioremap page-table updates to all
page-tables in the system at creation time and was thought to make
vmalloc faulting obsolete.

But that assumption was incredibly naive.

It turned out that there is a race window between the time the vmalloc
or ioremap code establishes a mapping and the time it synchronizes
this change to other page-tables in the system.

During this race window another CPU or thread can establish a vmalloc
mapping which uses the same intermediate page-table entries (e.g. PMD
or PUD) and does no synchronization in the end, because it found all
necessary mappings already present in the kernel reference page-table.

But when these intermediate page-table entries are not yet
synchronized, the other CPU or thread will continue with a vmalloc
address that is not yet mapped in the page-table it currently uses,
causing an unhandled page fault and oops like below:

	BUG: unable to handle page fault for address: fe80c000
	#PF: supervisor write access in kernel mode
	#PF: error_code(0x0002) - not-present page
	*pde = 33183067 *pte = a8648163
	Oops: 0002 [#1] SMP
	CPU: 1 PID: 13514 Comm: cve-2017-17053 Tainted: G
	...
	Call Trace:
	 ldt_dup_context+0x66/0x80
	 dup_mm+0x2b3/0x480
	 copy_process+0x133b/0x15c0
	 _do_fork+0x94/0x3e0
	 __ia32_sys_clone+0x67/0x80
	 __do_fast_syscall_32+0x3f/0x70
	 do_fast_syscall_32+0x29/0x60
	 do_SYSENTER_32+0x15/0x20
	 entry_SYSENTER_32+0x9f/0xf2
	EIP: 0xb7eef549

So the arch_sync_kernel_mappings() interface is racy, but removing it
would mean to re-introduce the vmalloc_sync_all() interface, which is
even more awful. Keep arch_sync_kernel_mappings() in place and catch
the race condition in the page-fault handler instead.

Do a partial revert of above commit to get vmalloc faulting on x86-32
back in place.

Fixes: 7f0a002b5a ("x86/mm: remove vmalloc faulting")
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200902155904.17544-1-joro@8bytes.org
2020-09-03 11:23:35 +02:00
arch x86/mm/32: Bring back vmalloc faulting on x86_32 2020-09-03 11:23:35 +02:00
block io_uring-5.9-2020-08-23 2020-08-24 11:53:15 -07:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2020-08-30 15:53:44 -07:00
Documentation A handful of documentation fixes for 5.9. 2020-08-31 12:46:00 -07:00
drivers Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/hid/hid 2020-09-02 12:55:46 -07:00
fs Fixes for 5.9: 2020-09-02 11:42:18 -07:00
include Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/hid/hid 2020-09-02 12:55:46 -07:00
init OpenRISC updates for 5.9 2020-08-14 14:04:53 -07:00
ipc treewide: Use fallthrough pseudo-keyword 2020-08-23 17:36:59 -05:00
kernel Three interrupt related fixes for X86: 2020-08-30 12:01:23 -07:00
lib lib: Revert use of fallthrough pseudo-keyword in lib/ 2020-08-24 14:17:44 -07:00
LICENSES
mm powerpc fixes for 5.9 #4 2020-08-30 10:56:12 -07:00
net Fixes: 2020-08-25 18:01:36 -07:00
samples treewide: Use fallthrough pseudo-keyword 2020-08-23 17:36:59 -05:00
scripts kconfig: qconf: replace deprecated QString::sprintf() with QTextStream 2020-08-21 10:23:38 +09:00
security treewide: Use fallthrough pseudo-keyword 2020-08-23 17:36:59 -05:00
sound treewide: Use fallthrough pseudo-keyword 2020-08-23 17:36:59 -05:00
tools perf tools fixes for v5.9: 2020-09-01 19:36:52 -07:00
usr Merge branch 'work.fdpic' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-08-07 13:29:39 -07:00
virt * PAE and PKU bugfixes for x86 2020-08-22 10:03:05 -07:00
.clang-format block: add bio_for_each_bvec_all() 2020-05-25 11:25:24 +02:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: Add ZSTD-compressed files 2020-07-31 11:50:49 +02:00
.mailmap Merge branch 'akpm' (patches from Andrew) 2020-08-21 14:44:48 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS CREDITS: Replace HTTP links with HTTPS ones 2020-07-23 14:53:58 -06:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS perf tools fixes for v5.9: 2020-09-01 19:36:52 -07:00
Makefile Linux 5.9-rc3 2020-08-30 16:01:54 -07:00
README

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.