Hi,
On 09/06/2021 03:34, Jordan Niethe wrote:
> From: Russell Currey <ruscur@xxxxxxxxxx>
>
> To enable strict module RWX on powerpc, set:
>
> CONFIG_STRICT_MODULE_RWX=y
>
> You should also have CONFIG_STRICT_KERNEL_RWX=y set to have any real
> security benefit.
>
> ARCH_HAS_STRICT_MODULE_RWX is set to require ARCH_HAS_STRICT_KERNEL_RWX.
> This is due to a quirk in arch/Kconfig and arch/powerpc/Kconfig that
> makes STRICT_MODULE_RWX *on by default* in configurations where
> STRICT_KERNEL_RWX is *unavailable*.
>
> Since this doesn't make much sense, and module RWX without kernel RWX
> doesn't make much sense, having the same dependencies as kernel RWX
> works around this problem.
>
> Book3s/32 603 and 604 core processors are not able to write protect
> kernel pages so do not set ARCH_HAS_STRICT_MODULE_RWX for Book3s/32.
>
> Reviewed-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
> Signed-off-by: Russell Currey <ruscur@xxxxxxxxxx>
> [jpn: - predicate on !PPC_BOOK3S_604
> - make module_alloc() use PAGE_KERNEL protection]
> Signed-off-by: Jordan Niethe <jniethe5@xxxxxxxxx>
> ---
> v10: - Predicate on !PPC_BOOK3S_604
> - Make module_alloc() use PAGE_KERNEL protection
> v11: - Neaten up
> v13: Use strict_kernel_rwx_enabled()
> v14: Make changes to module_alloc() its own commit
> v15: - Force STRICT_KERNEL_RWX if STRICT_MODULE_RWX is selected
> - Predicate on !PPC_BOOK3S_32 instead
> ---
> arch/powerpc/Kconfig | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index abfe2e9225fa..72f307f1796b 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -142,6 +142,7 @@ config PPC
> select ARCH_HAS_SCALED_CPUTIME if VIRT_CPU_ACCOUNTING_NATIVE && PPC_BOOK3S_64
> select ARCH_HAS_SET_MEMORY
> select ARCH_HAS_STRICT_KERNEL_RWX if ((PPC_BOOK3S_64 || PPC32) && !HIBERNATION)
> + select ARCH_HAS_STRICT_MODULE_RWX if ARCH_HAS_STRICT_KERNEL_RWX && !PPC_BOOK3S_32
> select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
> select ARCH_HAS_UACCESS_FLUSHCACHE
> select ARCH_HAS_UBSAN_SANITIZE_ALL
> @@ -267,6 +268,7 @@ config PPC
> select PPC_DAWR if PPC64
> select RTC_LIB
> select SPARSE_IRQ
> + select STRICT_KERNEL_RWX if STRICT_MODULE_RWX
> select SYSCTL_EXCEPTION_TRACE
> select THREAD_INFO_IN_TASK
> select VIRT_TO_BUS if !PPC64
>
since this patch is merged my VM is experiencing a crash at boot (20% of the time):
[ 8.496850] kernel tried to execute exec-protected page (c008000004073278) - exploit
attempt? (uid: 0)
[ 8.496921] BUG: Unable to handle kernel instruction fetch
[ 8.496954] Faulting instruction address: 0xc008000004073278
[ 8.496994] Oops: Kernel access of bad area, sig: 11 [#1]
[ 8.497028] LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA pSeries
[ 8.497071] Modules linked in: drm virtio_console fuse drm_panel_orientation_quirks xfs
libcrc32c virtio_net net_failover virtio_blk vmx_crypto failover dm_mirror dm_region_hash
dm_log dm_mod
[ 8.497186] CPU: 3 PID: 44 Comm: kworker/3:1 Not tainted 5.14.0-rc4+ #12
[ 8.497228] Workqueue: events control_work_handler [virtio_console]
[ 8.497272] NIP: c008000004073278 LR: c008000004073278 CTR: c0000000001e9de0
[ 8.497320] REGS: c00000002e4ef7e0 TRAP: 0400 Not tainted (5.14.0-rc4+)
[ 8.497361] MSR: 800000004280b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE> CR: 24002822
XER: 200400cf
[ 8.497426] CFAR: c0000000001e9e44 IRQMASK: 1
[ 8.497426] GPR00: c008000004073278 c00000002e4efa80 c000000002a26b00 c000000042c39520
[ 8.497426] GPR04: 0000000000000001 0000000000000000 0000000000000000 00000000000000ff
[ 8.497426] GPR08: 0000000000000001 c000000042c39520 0000000000000001 c008000004076008
[ 8.497426] GPR12: c0000000001e9de0 c0000001fffccb00 c00000000018ba88 c00000002c91d400
[ 8.497426] GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[ 8.497426] GPR20: 0000000000000000 0000000000000000 0000000000000000 c008000004080340
[ 8.497426] GPR24: c0080000040a01e8 0000000000000000 0000000000000000 c00000002e0975c0
[ 8.497426] GPR28: c00000002ce72940 c000000042c39520 0000000000000048 0000000000000038
[ 8.497891] NIP [c008000004073278] fill_queue+0xf0/0x210 [virtio_console]
[ 8.497934] LR [c008000004073278] fill_queue+0xf0/0x210 [virtio_console]
[ 8.497976] Call Trace:
[ 8.497993] [c00000002e4efa80] [c00800000407323c] fill_queue+0xb4/0x210
[virtio_console] (unreliable)
[ 8.498052] [c00000002e4efae0] [c008000004073a90] add_port+0x1a8/0x470 [virtio_console]
[ 8.498102] [c00000002e4efbb0] [c0080000040750f4] control_work_handler+0xbc/0x1e8
[virtio_console]
[ 8.498160] [c00000002e4efc60] [c00000000017f4f0] process_one_work+0x290/0x590
[ 8.498212] [c00000002e4efd00] [c00000000017f878] worker_thread+0x88/0x620
[ 8.498256] [c00000002e4efda0] [c00000000018bc14] kthread+0x194/0x1a0
[ 8.498299] [c00000002e4efe10] [c00000000000cf54] ret_from_kernel_thread+0x5c/0x64
[ 8.498349] Instruction dump:
[ 8.498374] 7da96b78 a14d0c8a 419c00b0 2f8a0000 419eff88 b32d0c8a 7c0004ac 4bffff7c
[ 8.498430] 60000000 60000000 7fa3eb78 48002d95 <e8410018> 38600000 480025e1 e8410018
[ 8.498485] ---[ end trace 16ee10903290b647 ]---
[ 8.501433]
[ 9.502601] Kernel panic - not syncing: Fatal exception
add_port+0x1a8/0x470 :
1420
1421 /* We can safely ignore ENOSPC because it means
1422 * the queue already has buffers. Buffers are removed
1423 * only by virtcons_remove(), not by unplug_port()
1424 */
->1425 err = fill_queue(port->in_vq, &port->inbuf_lock);
1426 if (err < 0 && err != -ENOSPC) {
1427 dev_err(port->dev, "Error allocating inbufs\n");
1428 goto free_device;
1429 }
fill_queue+0x90/0x210 :
1326 static int fill_queue(struct virtqueue *vq, spinlock_t *lock)
1327 {
1328 struct port_buffer *buf;
1329 int nr_added_bufs;
1330 int ret;
1331
1332 nr_added_bufs = 0;
1333 do {
1334 buf = alloc_buf(vq->vdev, PAGE_SIZE, 0);
1335 if (!buf)
1336 return -ENOMEM;
1337
->1338 spin_lock_irq(lock);
I'm using an upstream kernel (5.14-rc4, 251a1524293d) in the VM.
My host is a RHEL 8.5/POWER9: qemu-kvm-6.0.0-21 and kernel-4.18.0-325
My qemu command line is:
/usr/libexec/qemu-kvm \
-M pseries,accel=kvm \
-nographic -nodefaults \
-device virtio-serial-pci \
-device virtconsole \
-device virtio-net-pci,mac=9a:2b:2c:2d:2e:2f,netdev=hostnet0 \
-blockdev
node-name=disk1,file.driver=file,driver=qcow2,file.driver=file,file.filename=disk.qcow2 \
-netdev bridge,id=hostnet0,br=virbr0,helper=/usr/libexec/qemu-bridge-helper \
-device virtio-blk-pci,id=image1,drive=disk1 \
-m 8192 \
-smp 4 \
-serial mon:stdio
Do we need something in qemu/kvm to support STRICT_MODULE_RWX ?
Thanks,
Laurent
