[PATCH 5.10 5.15 1/3] io_uring/sqpoll: do not allow pinning outside of cpuset

[PATCH 5.10 5.15 1/3] io_uring/sqpoll: do not allow pinning outside of cpuset

[Felix Moessbauer]

commit f011c9cf04c06f16b24f583d313d3c012e589e50 upstream.

The submit queue polling threads are userland threads that just never
exit to the userland. When creating the thread with IORING_SETUP_SQ_AFF,
the affinity of the poller thread is set to the cpu specified in
sq_thread_cpu. However, this CPU can be outside of the cpuset defined
by the cgroup cpuset controller. This violates the rules defined by the
cpuset controller and is a potential issue for realtime applications.

In b7ed6d8ffd6 we fixed the default affinity of the poller thread, in
case no explicit pinning is required by inheriting the one of the
creating task. In case of explicit pinning, the check is more
complicated, as also a cpu outside of the parent cpumask is allowed.
We implemented this by using cpuset_cpus_allowed (that has support for
cgroup cpusets) and testing if the requested cpu is in the set.

Fixes: 37d1e2e3642e ("io_uring: move SQPOLL thread io-wq forked worker")
Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com>
Link: https://lore.kernel.org/r/20240909150036.55921-1-felix.moessbauer@siemens.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 io_uring/io_uring.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 8ed2c65529714..6b6fd244233f8 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -56,6 +56,7 @@
 #include <linux/mm.h>
 #include <linux/mman.h>
 #include <linux/percpu.h>
+#include <linux/cpuset.h>
 #include <linux/slab.h>
 #include <linux/blkdev.h>
 #include <linux/bvec.h>
@@ -8746,10 +8747,12 @@ static int io_sq_offload_create(struct io_ring_ctx *ctx,
 			return 0;
 
 		if (p->flags & IORING_SETUP_SQ_AFF) {
+			struct cpumask allowed_mask;
 			int cpu = p->sq_thread_cpu;
 
 			ret = -EINVAL;
-			if (cpu >= nr_cpu_ids || !cpu_online(cpu))
+			cpuset_cpus_allowed(current, &allowed_mask);
+			if (!cpumask_test_cpu(cpu, &allowed_mask))
 				goto err_sqpoll;
 			sqd->sq_cpu = cpu;
 		} else {
-- 
2.39.5

[PATCH 5.10 5.15 2/3] io_uring/sqpoll: retain test for whether the CPU is valid

[Felix Moessbauer]

From: Jens Axboe <axboe@kernel.dk>

commit a09c17240bdf2e9fa6d0591afa9448b59785f7d4 upstream.

A recent commit ensured that SQPOLL cannot be setup with a CPU that
isn't in the current tasks cpuset, but it also dropped testing whether
the CPU is valid in the first place. Without that, if a task passes in
a CPU value that is too high, the following KASAN splat can get
triggered:

BUG: KASAN: stack-out-of-bounds in io_sq_offload_create+0x858/0xaa4
Read of size 8 at addr ffff800089bc7b90 by task wq-aff.t/1391

CPU: 4 UID: 1000 PID: 1391 Comm: wq-aff.t Not tainted 6.11.0-rc7-00227-g371c468f4db6 #7080
Hardware name: linux,dummy-virt (DT)
Call trace:
 dump_backtrace.part.0+0xcc/0xe0
 show_stack+0x14/0x1c
 dump_stack_lvl+0x58/0x74
 print_report+0x16c/0x4c8
 kasan_report+0x9c/0xe4
 __asan_report_load8_noabort+0x1c/0x24
 io_sq_offload_create+0x858/0xaa4
 io_uring_setup+0x1394/0x17c4
 __arm64_sys_io_uring_setup+0x6c/0x180
 invoke_syscall+0x6c/0x260
 el0_svc_common.constprop.0+0x158/0x224
 do_el0_svc+0x3c/0x5c
 el0_svc+0x34/0x70
 el0t_64_sync_handler+0x118/0x124
 el0t_64_sync+0x168/0x16c

The buggy address belongs to stack of task wq-aff.t/1391
 and is located at offset 48 in frame:
 io_sq_offload_create+0x0/0xaa4

This frame has 1 object:
 [32, 40) 'allowed_mask'

The buggy address belongs to the virtual mapping at
 [ffff800089bc0000, ffff800089bc9000) created by:
 kernel_clone+0x124/0x7e0

The buggy address belongs to the physical page:
page: refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff0000d740af80 pfn:0x11740a
memcg:ffff0000c2706f02
flags: 0xbffe00000000000(node=0|zone=2|lastcpupid=0x1fff)
raw: 0bffe00000000000 0000000000000000 dead000000000122 0000000000000000
raw: ffff0000d740af80 0000000000000000 00000001ffffffff ffff0000c2706f02
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff800089bc7a80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff800089bc7b00: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1
>ffff800089bc7b80: 00 f3 f3 f3 00 00 00 00 00 00 00 00 00 00 00 00
                         ^
 ffff800089bc7c00: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1
 ffff800089bc7c80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 f3

Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202409161632.cbeeca0d-lkp@intel.com
Fixes: f011c9cf04c0 ("io_uring/sqpoll: do not allow pinning outside of cpuset")
Tested-by: Felix Moessbauer <felix.moessbauer@siemens.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com>
---
 io_uring/io_uring.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 6b6fd244233f8..a260852a0490c 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -8751,6 +8751,8 @@ static int io_sq_offload_create(struct io_ring_ctx *ctx,
 			int cpu = p->sq_thread_cpu;
 
 			ret = -EINVAL;
+			if (cpu >= nr_cpu_ids || !cpu_online(cpu))
+				goto err_sqpoll;
 			cpuset_cpus_allowed(current, &allowed_mask);
 			if (!cpumask_test_cpu(cpu, &allowed_mask))
 				goto err_sqpoll;
-- 
2.39.5

[PATCH 5.10 5.15 3/3] io_uring/sqpoll: do not put cpumask on stack

[Felix Moessbauer]

commit 7f44beadcc11adb98220556d2ddbe9c97aa6d42d upstream.

Putting the cpumask on the stack is deprecated for a long time (since
2d3854a37e8), as these can be big. Given that, change the on-stack
allocation of allowed_mask to be dynamically allocated.

Fixes: f011c9cf04c0 ("io_uring/sqpoll: do not allow pinning outside of cpuset")
Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com>
Link: https://lore.kernel.org/r/20240916111150.1266191-1-felix.moessbauer@siemens.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 io_uring/io_uring.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index a260852a0490c..12aade2ac68ea 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -8747,15 +8747,22 @@ static int io_sq_offload_create(struct io_ring_ctx *ctx,
 			return 0;
 
 		if (p->flags & IORING_SETUP_SQ_AFF) {
-			struct cpumask allowed_mask;
+			cpumask_var_t allowed_mask;
 			int cpu = p->sq_thread_cpu;
 
 			ret = -EINVAL;
 			if (cpu >= nr_cpu_ids || !cpu_online(cpu))
 				goto err_sqpoll;
-			cpuset_cpus_allowed(current, &allowed_mask);
-			if (!cpumask_test_cpu(cpu, &allowed_mask))
+			ret = -ENOMEM;
+			if (!alloc_cpumask_var(&allowed_mask, GFP_KERNEL))
+				goto err_sqpoll;
+			ret = -EINVAL;
+			cpuset_cpus_allowed(current, allowed_mask);
+			if (!cpumask_test_cpu(cpu, allowed_mask)) {
+				free_cpumask_var(allowed_mask);
 				goto err_sqpoll;
+			}
+			free_cpumask_var(allowed_mask);
 			sqd->sq_cpu = cpu;
 		} else {
 			sqd->sq_cpu = -1;
-- 
2.39.5

Re: [PATCH 5.10 5.15 1/3] io_uring/sqpoll: do not allow pinning outside of cpuset

[Greg KH]

On Thu, Oct 17, 2024 at 01:50:27PM +0200, Felix Moessbauer wrote:
> commit f011c9cf04c06f16b24f583d313d3c012e589e50 upstream.

All now queued up, thanks.

greg k-h