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Mark Rutland 975554b03e io_uring: fix SQPOLL cpu validation 
In io_sq_offload_start(), we call cpu_possible() on an unbounded cpu
value from userspace. On v5.1-rc7 on arm64 with
CONFIG_DEBUG_PER_CPU_MAPS, this results in a splat:

  WARNING: CPU: 1 PID: 27601 at include/linux/cpumask.h:121 cpu_max_bits_warn include/linux/cpumask.h:121 [inline]

There was an attempt to fix this in commit:

  917257daa0 ("io_uring: only test SQPOLL cpu after we've verified it")

... by adding a check after the cpu value had been limited to NR_CPU_IDS
using array_index_nospec(). However, this left an unbound check at the
start of the function, for which the warning still fires.

Let's fix this correctly by checking that the cpu value is bound by
nr_cpu_ids before passing it to cpu_possible(). Note that only
nr_cpu_ids of a cpumask are guaranteed to exist at runtime, and
nr_cpu_ids can be significantly smaller than NR_CPUs. For example, an
arm64 defconfig has NR_CPUS=256, while my test VM has 4 vCPUs.

Following the intent from the commit message for 917257daa0, the
check is moved under the SQ_AFF branch, which is the only branch where
the cpu values is consumed. The check is performed before bounding the
value with array_index_nospec() so that we don't silently accept bogus
cpu values from userspace, where array_index_nospec() would force these
values to 0.

I suspect we can remove the array_index_nospec() call entirely, but I've
conservatively left that in place, updated to use nr_cpu_ids to match
the prior check.

Tested on arm64 with the Syzkaller reproducer:

  https://syzkaller.appspot.com/bug?extid=cd714a07c6de2bc34293
  https://syzkaller.appspot.com/x/repro.syz?x=15d8b397200000

Full splat from before this patch:

WARNING: CPU: 1 PID: 27601 at include/linux/cpumask.h:121 cpu_max_bits_warn include/linux/cpumask.h:121 [inline]
WARNING: CPU: 1 PID: 27601 at include/linux/cpumask.h:121 cpumask_check include/linux/cpumask.h:128 [inline]
WARNING: CPU: 1 PID: 27601 at include/linux/cpumask.h:121 cpumask_test_cpu include/linux/cpumask.h:344 [inline]
WARNING: CPU: 1 PID: 27601 at include/linux/cpumask.h:121 io_sq_offload_start fs/io_uring.c:2244 [inline]
WARNING: CPU: 1 PID: 27601 at include/linux/cpumask.h:121 io_uring_create fs/io_uring.c:2864 [inline]
WARNING: CPU: 1 PID: 27601 at include/linux/cpumask.h:121 io_uring_setup+0x1108/0x15a0 fs/io_uring.c:2916
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 27601 Comm: syz-executor.0 Not tainted 5.1.0-rc7 #3
Hardware name: linux,dummy-virt (DT)
Call trace:
 dump_backtrace+0x0/0x2f0 include/linux/compiler.h:193
 show_stack+0x20/0x30 arch/arm64/kernel/traps.c:158
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x110/0x190 lib/dump_stack.c:113
 panic+0x384/0x68c kernel/panic.c:214
 __warn+0x2bc/0x2c0 kernel/panic.c:571
 report_bug+0x228/0x2d8 lib/bug.c:186
 bug_handler+0xa0/0x1a0 arch/arm64/kernel/traps.c:956
 call_break_hook arch/arm64/kernel/debug-monitors.c:301 [inline]
 brk_handler+0x1d4/0x388 arch/arm64/kernel/debug-monitors.c:316
 do_debug_exception+0x1a0/0x468 arch/arm64/mm/fault.c:831
 el1_dbg+0x18/0x8c
 cpu_max_bits_warn include/linux/cpumask.h:121 [inline]
 cpumask_check include/linux/cpumask.h:128 [inline]
 cpumask_test_cpu include/linux/cpumask.h:344 [inline]
 io_sq_offload_start fs/io_uring.c:2244 [inline]
 io_uring_create fs/io_uring.c:2864 [inline]
 io_uring_setup+0x1108/0x15a0 fs/io_uring.c:2916
 __do_sys_io_uring_setup fs/io_uring.c:2929 [inline]
 __se_sys_io_uring_setup fs/io_uring.c:2926 [inline]
 __arm64_sys_io_uring_setup+0x50/0x70 fs/io_uring.c:2926
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall arch/arm64/kernel/syscall.c:47 [inline]
 el0_svc_common.constprop.0+0x148/0x2e0 arch/arm64/kernel/syscall.c:83
 el0_svc_handler+0xdc/0x100 arch/arm64/kernel/syscall.c:129
 el0_svc+0x8/0xc arch/arm64/kernel/entry.S:948
SMP: stopping secondary CPUs
Dumping ftrace buffer:
   (ftrace buffer empty)
Kernel Offset: disabled
CPU features: 0x002,23000438
Memory Limit: none
Rebooting in 1 seconds..

Fixes: 917257daa0 ("io_uring: only test SQPOLL cpu after we've verified it")
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: linux-block@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org

Simplied the logic

Signed-off-by: Jens Axboe <axboe@kernel.dk>
History 2019-05-01 08:38:37 -06:00
arch A small number of ARM fixes 2019-04-28 10:50:57 -07:00
block bfq: update internal depth state when queue depth changes 2019-04-13 19:08:22 -06:00
certs kexec, KEYS: Make use of platform keyring for signature verify 2019-02-04 17:34:07 -05:00
crypto crypto: lrw - Fix atomic sleep when walking skcipher 2019-04-18 22:13:46 +08:00
Documentation mm: do not boost watermarks to avoid fragmentation for the DISCONTIG memory model 2019-04-26 09:18:05 -07:00
drivers 5.1 Third RC pull request 2019-04-28 10:00:45 -07:00
fs io_uring: fix SQPOLL cpu validation 2019-05-01 08:38:37 -06:00
include 5.1 Third RC pull request 2019-04-28 10:00:45 -07:00
init init: initialize jump labels before command line option parsing 2019-04-19 09:46:05 -07:00
ipc Merge branch 'work.mount' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2019-03-12 14:08:19 -07:00
kernel Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2019-04-27 10:18:40 -07:00
lib lib/test_vmalloc.c: do not create cpumask_t variable on stack 2019-04-26 09:18:05 -07:00
LICENSES LICENSES: Add GCC runtime library exception text 2019-01-16 14:54:15 -07:00
mm mm/page_alloc.c: fix never set ALLOC_NOFRAGMENT flag 2019-04-26 09:18:05 -07:00
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-04-24 16:18:59 -07:00
samples Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-03-11 08:54:01 -07:00
scripts locking/atomics: Don't assume that scripts are executable 2019-04-19 14:21:43 +02:00
security Merge branch 'for-5.1-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup 2019-04-19 18:03:55 -07:00
sound ALSA: hda/realtek - add two more pin configuration sets to quirk table 2019-04-17 10:41:38 +02:00
tools Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2019-04-24 16:18:59 -07:00
usr user/Makefile: Fix typo and capitalization in comment section 2018-12-11 00:18:03 +09:00
virt KVM: fix spectrev1 gadgets 2019-04-16 15:38:07 +02:00
.clang-format clang-format: Update with the latest for_each macro list 2019-04-12 12:49:54 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Add hch to .get_maintainer.ignore 2015-08-21 14:30:10 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore kbuild: Add support for DT binding schema checks 2018-12-13 09:41:32 -06:00
.mailmap Update Nicolas Pitre's email address 2019-04-02 18:12:44 -10:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS Char/Misc driver patches for 5.1-rc1 2019-03-06 14:18:59 -08:00
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 LED update for 5.1-rc7. 2019-04-24 16:15:38 -07:00
Makefile Linux 5.1-rc7 2019-04-28 17:04:13 -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.