[PATCH v3 0/2] arm64: livepatch: Enable livepatch without sframe

Song Liu
2025-03-20T17:16:08Z

There are recent efforts to enable livepatch for arm64, with sframe [1] or
without sframe [2]. This set tries to enable livepatch without sframe. Some
of the code, however, are from [1].

Although the sframe implementation is more promising in longer term, it
suffers from the following issues:

1. sframe is not yet supported in llvm;
2. There is still bug in binutil [3], so that we cannot yet use sframe
with gcc;
3. sframe unwinder hasn't been fully verified in the kernel.

On the other hand, arm64 processors have become more and more important in
the data center world. Therefore, it is getting critical to support
livepatching of arm64 kernels.

With recent change in arm64 unwinder [4], it is possible to reliably
livepatch arm64 kernels without sframe. This is because we do not need
arch_stack_walk_reliable() to get reliable stack trace in all scenarios.
Instead, we only need arch_stack_walk_reliable() to detect when the
stack trace is not reliable, then the livepatch logic can retry the patch
transition at a later time.

Given the increasing need of livepatching, and relatively long time before
sframe is fully ready (for both gcc and clang), we would like to enable
livepatch without sframe.

Thanks!

[1] https://lore.kernel.org/live-patching/20250127213310.2496133-1-wnliu@google.com/
[2] https://lore.kernel.org/live-patching/20250129232936.1795412-1-song@kernel.org/
[3] https://sourceware.org/bugzilla/show_bug.cgi?id=32589
[4] https://lore.kernel.org/linux-arm-kernel/20241017092538.1859841-1-mark.rutland@arm.com/

Changes v2 => v3:
1. Remove a redundant check for -ENOENT. (Josh Poimboeuf)
2. Add Tested-by and Acked-by on v1. (I forgot to add them in v2.)

v2: https://lore.kernel.org/live-patching/20250319213707.1784775-1-song@kernel.org/

Changes v1 => v2:

1. Rework arch_stack_walk_reliable().

v1: https://lore.kernel.org/live-patching/20250308012742.3208215-1-song@kernel.org/

Song Liu (2):
arm64: Implement arch_stack_walk_reliable
arm64: Implement HAVE_LIVEPATCH

arch/arm64/Kconfig | 3 ++
arch/arm64/include/asm/thread_info.h | 4 +-
arch/arm64/kernel/entry-common.c | 4 ++
arch/arm64/kernel/stacktrace.c | 66 +++++++++++++++++++++-------
4 files changed, 60 insertions(+), 17 deletions(-)

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2.47.1