Re: [PATCH 0/8] unwind, arm64: add sframe unwinder for kernel

Indu Bhagat
2025-02-13T00:10:32Z

On 2/12/25 3:32 PM, Song Liu wrote:
> I run some tests with this set and my RFC set [1]. Most of
> the test is done with kpatch-build. I tested both Puranjay's
> version [3] and my version [4].
>
> For gcc 14.2.1, I have seen the following issue with this
> test [2]. This happens with both upstream and 6.13.2.
> The livepatch loaded fine, but the system spilled out the
> following warning quickly.
>

In presence of the issue
https://sourceware.org/bugzilla/show_bug.cgi?id=32666, I'd expect bad
data in SFrame section. Which may be causing this symptom?

To be clear, the issue affects loaded kernel modules. I cannot tell for
certain - is there module loading involved in your test ?

> On the other hand, the same test works with LLVM and
> my RFC set (LLVM doesn't support SFRAME, and thus
> doesn't work with this set yet).
>
> Thanks,
> Song
>
>
> [ 81.250437] ------------[ cut here ]------------
> [ 81.250818] refcount_t: saturated; leaking memory.
> [ 81.251201] WARNING: CPU: 0 PID: 95 at lib/refcount.c:22
> refcount_warn_saturate+0x6c/0x140
> [ 81.251841] Modules linked in: livepatch_special_static(OEK)
> [ 81.252277] CPU: 0 UID: 0 PID: 95 Comm: bash Tainted: G
> OE K 6.13.2-00321-g52d2813b4b07 #49
> [ 81.253003] Tainted: [O]=OOT_MODULE, [E]=UNSIGNED_MODULE, [K]=LIVEPATCH
> [ 81.253503] Hardware name: linux,dummy-virt (DT)
> [ 81.253856] pstate: 634000c5 (nZCv daIF +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
> [ 81.254383] pc : refcount_warn_saturate+0x6c/0x140
> [ 81.254748] lr : refcount_warn_saturate+0x6c/0x140
> [ 81.255114] sp : ffff800085a6fc00
> [ 81.255371] x29: ffff800085a6fc00 x28: 0000000001200000 x27: ffff0000c2966180
> [ 81.255918] x26: 0000000000000000 x25: ffff8000829c0000 x24: ffff0000c2e9b608
> [ 81.256462] x23: ffff800083351000 x22: ffff0000c2e9af80 x21: ffff0000c062e140
> [ 81.257006] x20: ffff0000c1c10c00 x19: ffff800085a6fd80 x18: ffffffffffffffff
> [ 81.257544] x17: 0000000000000001 x16: ffffffffffffffff x15: 0000000000000006
> [ 81.258083] x14: 0000000000000000 x13: 2e79726f6d656d20 x12: 676e696b61656c20
> [ 81.258625] x11: ffff8000829f7d70 x10: 0000000000000147 x9 : ffff8000801546b4
> [ 81.259165] x8 : 00000000fffeffff x7 : 00000000ffff0000 x6 : ffff800082f77d70
> [ 81.259709] x5 : 80000000ffff0000 x4 : 0000000000000000 x3 : 0000000000000001
> [ 81.260257] x2 : ffff8000829f7a88 x1 : ffff8000829f7a88 x0 : 0000000000000026
> [ 81.260824] Call trace:
> [ 81.261015] refcount_warn_saturate+0x6c/0x140 (P)
> [ 81.261387] __refcount_add.constprop.0+0x60/0x70
> [ 81.261748] copy_process+0xfdc/0xfd58 [livepatch_special_static]
> [ 81.262217] kernel_clone+0x80/0x3e0
> [ 81.262499] __do_sys_clone+0x5c/0x88
> [ 81.262786] __arm64_sys_clone+0x24/0x38
> [ 81.263085] invoke_syscall+0x4c/0x108
> [ 81.263378] el0_svc_common.constprop.0+0x44/0xe8
> [ 81.263734] do_el0_svc+0x20/0x30
> [ 81.263993] el0_svc+0x34/0xf8
> [ 81.264231] el0t_64_sync_handler+0x104/0x130
> [ 81.264561] el0t_64_sync+0x184/0x188
> [ 81.264846] ---[ end trace 0000000000000000 ]---
> [ 82.335559] ------------[ cut here ]------------
> [ 82.335931] refcount_t: underflow; use-after-free.
> [ 82.336307] WARNING: CPU: 1 PID: 0 at lib/refcount.c:28
> refcount_warn_saturate+0xec/0x140
> [ 82.336949] Modules linked in: livepatch_special_static(OEK)
> [ 82.337389] CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Tainted: G
> W OE K 6.13.2-00321-g52d2813b4b07 #49
> [ 82.338148] Tainted: [W]=WARN, [O]=OOT_MODULE, [E]=UNSIGNED_MODULE,
> [K]=LIVEPATCH
> [ 82.338721] Hardware name: linux,dummy-virt (DT)
> [ 82.339083] pstate: 63400005 (nZCv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
> [ 82.339617] pc : refcount_warn_saturate+0xec/0x140
> [ 82.340007] lr : refcount_warn_saturate+0xec/0x140
> [ 82.340378] sp : ffff80008370fe40
> [ 82.340637] x29: ffff80008370fe40 x28: 0000000000000000 x27: 0000000000000000
> [ 82.341188] x26: 000000000000000a x25: ffff0000fdaf7ab8 x24: 0000000000000014
> [ 82.341737] x23: ffff8000829c8d30 x22: ffff80008370ff28 x21: ffff0000fe020000
> [ 82.342286] x20: ffff0000c062e140 x19: ffff0000c2e9af80 x18: ffffffffffffffff
> [ 82.342839] x17: ffff80007b7a0000 x16: ffff800083700000 x15: 0000000000000006
> [ 82.343389] x14: 0000000000000000 x13: 2e656572662d7265 x12: 7466612d65737520
> [ 82.343944] x11: ffff8000829f7d70 x10: 000000000000016a x9 : ffff8000801546b4
> [ 82.344499] x8 : 00000000fffeffff x7 : 00000000ffff0000 x6 : ffff800082f77d70
> [ 82.345051] x5 : 80000000ffff0000 x4 : 0000000000000000 x3 : 0000000000000001
> [ 82.345604] x2 : ffff8000829f7a88 x1 : ffff8000829f7a88 x0 : 0000000000000026
> [ 82.346163] Call trace:
> [ 82.346359] refcount_warn_saturate+0xec/0x140 (P)
> [ 82.346736] __put_task_struct+0x130/0x170
> [ 82.347063] delayed_put_task_struct+0xbc/0xe8
> [ 82.347411] rcu_core+0x20c/0x5f8
> [ 82.347680] rcu_core_si+0x14/0x28
> [ 82.347952] handle_softirqs+0x124/0x308
> [ 82.348260] __do_softirq+0x18/0x20
> [ 82.348536] ____do_softirq+0x14/0x28
> [ 82.348828] call_on_irq_stack+0x24/0x30
> [ 82.349137] do_softirq_own_stack+0x20/0x38
> [ 82.349465] __irq_exit_rcu+0xcc/0x108
> [ 82.349764] irq_exit_rcu+0x14/0x28
> [ 82.350038] el1_interrupt+0x34/0x50
> [ 82.350321] el1h_64_irq_handler+0x14/0x20
> [ 82.350642] el1h_64_irq+0x6c/0x70
> [ 82.350911] default_idle_call+0x30/0xd0 (P)
> [ 82.351248] do_idle+0x1d0/0x200
> [ 82.351506] cpu_startup_entry+0x38/0x48
> [ 82.351818] secondary_start_kernel+0x124/0x150
> [ 82.352176] __secondary_switched+0xac/0xb0
> [ 82.352505] ---[ end trace 0000000000000000 ]---
>
>
>
> [1] SFRAME-less livepatch RFC
> https://lore.kernel.org/live-patching/20250129232936.1795412-1-song@kernel.org/
> [2] special-static test from kpatch
> https://github.com/dynup/kpatch/blob/master/test/integration/linux-6.2.0/special-static.patch
> [3] Puranjay's kpatch with arm64 support
> https://github.com/puranjaymohan/kpatch/tree/arm64
> [4] My version of kpatch with arm64 and LTO support
> https://github.com/liu-song-6/kpatch/tree/fb-6.13-v2
>
> On Mon, Jan 27, 2025 at 1:33 PM Weinan Liu <wnliu@google.com> wrote:
>>
>> This patchset implements a generic kernel sframe-based [1] unwinder.
>> The main goal is to support reliable stacktraces on arm64.
>>
>> On x86 orc unwinder provides reliable stacktraces. But arm64 misses the
>> required support from objtool: it cannot generate orc unwind tables for
>> arm64.
>>
>> Currently, there's already a sframe unwinder proposed for userspace: [2].
>> Since the sframe unwind table algorithm is similar, these two proposal
>> could integrate common functionality in the future.
>>
>> There are some incomplete features or challenges:
>> - The unwinder doesn't yet work with kernel modules. The `start_addr` of
>> FRE from kernel modules doesn't appear correct, preventing us from
>> unwinding functions from kernel modules.
>> - Currently, only GCC supports sframe.
>>
>> Ref:
>> [1]: https://sourceware.org/binutils/docs/sframe-spec.html
>> [2]: https://lore.kernel.org/lkml/cover.1730150953.git.jpoimboe@kernel.org/
>>
>> Madhavan T. Venkataraman (1):
>> arm64: Define TIF_PATCH_PENDING for livepatch
>>
>> Weinan Liu (7):
>> unwind: build kernel with sframe info
>> arm64: entry: add unwind info for various kernel entries
>> unwind: add sframe v2 header
>> unwind: Implement generic sframe unwinder library
>> unwind: arm64: Add sframe unwinder on arm64
>> unwind: arm64: add reliable stacktrace support for arm64
>> arm64: Enable livepatch for ARM64
>>
>> Makefile | 6 +
>> arch/Kconfig | 8 +
>> arch/arm64/Kconfig | 3 +
>> arch/arm64/Kconfig.debug | 10 +
>> arch/arm64/include/asm/stacktrace/common.h | 6 +
>> arch/arm64/include/asm/thread_info.h | 4 +-
>> arch/arm64/kernel/entry-common.c | 4 +
>> arch/arm64/kernel/entry.S | 10 +
>> arch/arm64/kernel/setup.c | 2 +
>> arch/arm64/kernel/stacktrace.c | 102 ++++++++++
>> include/asm-generic/vmlinux.lds.h | 12 ++
>> include/linux/sframe_lookup.h | 43 +++++
>> kernel/Makefile | 1 +
>> kernel/sframe.h | 215 +++++++++++++++++++++
>> kernel/sframe_lookup.c | 196 +++++++++++++++++++
>> 15 files changed, 621 insertions(+), 1 deletion(-)
>> create mode 100644 include/linux/sframe_lookup.h
>> create mode 100644 kernel/sframe.h
>> create mode 100644 kernel/sframe_lookup.c
>>
>> --
>> 2.48.1.262.g85cc9f2d1e-goog
>>
>>