On 12/22/2015 02:37 AM, Geert Uytterhoeven wrote:
Hi Kees, Russell,
On Wed, Dec 2, 2015 at 9:27 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
The use of CONFIG_DEBUG_RODATA is generally seen as an essential part of
kernel self-protection:
http://www.openwall.com/lists/kernel-hardening/2015/11/30/13
Additionally, its name has grown to mean things beyond just rodata. To
get ARM closer to this, we ought to rearrange the names of the configs
that control how the kernel protects its memory. What was called
CONFIG_ARM_KERNMEM_PERMS is really doing the work that other architectures
call CONFIG_DEBUG_RODATA.
[...]
This broke s2ram with shmobile_defconfig on r8a7791/koelsch:
Freezing user space processes ... (elapsed 0.002 seconds) done.
Freezing remaining freezable tasks ... (elapsed 0.003 seconds) done.
PM: suspend of devices complete after 112.157 msecs
PM: late suspend of devices complete after 1.605 msecs
PM: noirq suspend of devices complete after 13.098 msecs
Disabling non-boot CPUs ...
s---[ end Kernel panic - not syncing: Attempted to kill the idle task!
CPU0: stopping
CPU: 0 PID: 2412 Comm: s2ram Tainted: G D
4.4.0-rc6-00003-g1bb20571dcf0edfc #470
Hardware name: Generic R8A7791 (Flattened Device Tree)
Backtrace:
[<c010a92c>] (dump_backtrace) from [<c010aad4>] (show_stack+0x18/0x1c)
r6:00000000 r5:00000000 r4:00000000 r3:80404000
[<c010aabc>] (show_stack) from [<c02b9ff4>] (dump_stack+0x78/0x94)
[<c02b9f7c>] (dump_stack) from [<c010d4b4>] (handle_IPI+0xf4/0x19c)
r4:c09313f0 r3:c09091ec
[<c010d3c0>] (handle_IPI) from [<c0101430>] (gic_handle_irq+0x7c/0x98)
r7:c0910b80 r6:ee1d5c30 r5:c0902754 r4:f0802000
[<c01013b4>] (gic_handle_irq) from [<c010b654>] (__irq_svc+0x54/0x70)
Exception stack(0xee1d5c30 to 0xee1d5c78)
5c20: c0955484 00000002
00000000 60070013
5c40: c0942718 c093916c 00000005 0000000f 00000000 00000000
c0943088 ee1d5cd4
5c60: ee1d5c08 ee1d5c80 c033fc20 c0158120 60070013 ffffffff
r8:00000000 r7:ee1d5c64 r6:ffffffff r5:60070013 r4:c0158120 r3:c033fc20
[<c0157ecc>] (console_unlock) from [<c0158724>] (vprintk_emit+0x448/0x4a4)
r10:c09450a6 r9:00000000 r8:0000000e r7:00000005 r6:00000006 r5:c0932758
r4:00000001
[<c01582dc>] (vprintk_emit) from [<c01588e0>] (vprintk_default+0x28/0x30)
r10:c09055e0 r9:00000001 r8:c09055e0 r7:00000010 r6:00000000 r5:00000000
r4:00000001
[<c01588b8>] (vprintk_default) from [<c018e538>] (printk+0x34/0x40)
[<c018e508>] (printk) from [<c010cfb8>] (__cpu_die+0x34/0x78)
r3:00000003 r2:c0906808 r1:00000001 r0:c0710af6
[<c010cf84>] (__cpu_die) from [<c011d7d0>] (_cpu_down+0x168/0x290)
r4:00000001 r3:00000005
[<c011d668>] (_cpu_down) from [<c011dd90>] (disable_nonboot_cpus+0x70/0xf0)
r10:00000051 r9:c0932734 r8:c0902528 r7:00000000 r6:c090245c r5:c0931b40
r4:00000001
[<c011dd20>] (disable_nonboot_cpus) from [<c0155fd8>]
(suspend_devices_and_enter+0x290/0x3f8)
r8:c0714bb5 r7:eebac300 r6:00000003 r5:c0932734 r4:00000000 r3:00000000
[<c0155d48>] (suspend_devices_and_enter) from [<c01561f4>]
(pm_suspend+0xb4/0x1c8)
r9:c093273c r8:c0714bb5 r7:eebac300 r6:00000003 r5:c09576fc r4:00000000
[<c0156140>] (pm_suspend) from [<c0155148>] (state_store+0xb0/0xc4)
r6:00000004 r5:00000003 r4:00000003 r3:0000006d
[<c0155098>] (state_store) from [<c02bbce8>] (kobj_attr_store+0x1c/0x28)
r9:000cdc08 r8:ee1d5f80 r7:eebacb0c r6:eebacb00 r5:eebac300 r4:eebac300
[<c02bbccc>] (kobj_attr_store) from [<c0222438>] (sysfs_kf_write+0x44/0x50)
[<c02223f4>] (sysfs_kf_write) from [<c0221ae0>]
(kernfs_fop_write+0x13c/0x1a0)
r4:00000004 r3:c02223f4
[<c02219a4>] (kernfs_fop_write) from [<c01ca1b4>] (__vfs_write+0x34/0xdc)
r10:00000000 r9:ee1d4000 r8:c0106fa4 r7:00000004 r6:ee1d5f80 r5:c02219a4
r4:edf85d00
[<c01ca180>] (__vfs_write) from [<c01ca3dc>] (vfs_write+0xb8/0x140)
r7:ee1d5f80 r6:000cdc08 r5:edf85d00 r4:00000004
[<c01ca324>] (vfs_write) from [<c01ca544>] (SyS_write+0x50/0x90)
r9:ee1d4000 r8:c0106fa4 r7:000cdc08 r6:00000004 r5:edf85d00 r4:edf85d00
[<c01ca4f4>] (SyS_write) from [<c0106de0>] (ret_fast_syscall+0x0/0x3c)
Before commit 1bb20571dcf0edfc ("ARM: 8470/1: mm: flip priority of
CONFIG_DEBUG_RODATA"):
# CONFIG_ARM_KERNMEM_PERMS is not set
Freezing user space processes ... (elapsed 0.001 seconds) done.
Freezing remaining freezable tasks ... (elapsed 0.003 seconds) done.
PM: suspend of devices complete after 112.163 msecs
PM: late suspend of devices complete after 1.610 msecs
PM: noirq suspend of devices complete after 13.109 msecs
Disabling non-boot CPUs ...
CPU1: shutdown
After the offending commit:
CONFIG_DEBUG_RODATA=y
CONFIG_DEBUG_ALIGN_RODATA=y
The "problem" is that DEBUG_RODATA now defaults to y on CPU_V7, so it gets
enabled for shmobile_defconfig. If I manually disable DEBUG_RODATA again,
s2ram does work.
The real problem is something else, though. I can trigger the same panic
without the offending commit by enabling:
CONFIG_ARM_KERNMEM_PERMS=y
CONFIG_DEBUG_RODATA=y
I never enabled those options before, so I have no idea if this is a recent
regression. I've just tried a few older versions: on v4.4-rc1 I see the same
panic, on v4.3 (and v4.3.3) I don't see the panic, and the "CPU1: shutdown"
line, but the system doesn't wake up.
Thanks for your suggestions!
Gr{oetje,eeting}s,
Geert
At a thought I think the RO/NX persmission are working as expected and
something in the suspend code is writing or executing from where it
shouldn't. I hit similar problems when working on RO/NX support for
arm64.
Looking in arch/arm/mach-shmobile/headsmp.S, it looks like
shmobile_boot_fn, shmobile_boot_arg, shmobile_smp_mpdir, shmobile_smp_fn,
and shmobile_smp_arg are ending up in the the text section which is going
to be read_only. Assuming I understand the code flow, it looks like those
are modified at suspend time which isn't going to work. I would say just
throw those objects in the .data section but I notice shmobile_boot_size
is there as well which seems to be calculated based off of the boot
vector so you might need to do some re-working there.
Thanks,
Laura
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