On Fri, Apr 04, 2025 at 03:58:36PM +0800, Kang Wenlin wrote:
Hi Greg
Thanks for your response.
On 4/3/2025 22:52, Greg KH wrote:
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On Wed, Apr 02, 2025 at 04:26:50PM +0800, Kang Wenlin wrote:
From: Wenlin Kang wenlin.kang@windriver.com
The selftest tpdir2 terminated with a 'Segmentation fault' during loading.
root@localhost:~# cd linux-kenel/tools/testing/selftests/arm64/abi && make root@localhost:~/linux-kernel/tools/testing/selftests/arm64/abi# ./tpidr2 Segmentation fault
The cause of this is the __arch_clear_user() failure.
load_elf_binary() [fs/binfmt_elf.c] -> if (likely(elf_bss != elf_brk) && unlikely(padzero(elf_bes))) -> padzero() -> clear_user() [arch/arm64/include/asm/uaccess.h] -> __arch_clear_user() [arch/arm64/lib/clear_user.S]
For more details, please see: https://lore.kernel.org/lkml/1d0342f3-0474-482b-b6db-81ca7820a462@t-8ch.de/T...
This is just a userspace issue (i.e. don't do that, and if you do want to do that, use a new kernel!)
Why do these changes need to be backported, do you have real users that are crashing in this way to require these changes?
This issue was identified during our internal testing, and I found similar cases discussed in the link above. Upon reviewing the kernel code, I noticed that a patch series already accepted into mainline addresses this problem. Since these patches are already upstream and effectively resolve the issue, I decided to backport them. We believe this provides a more robust and maintainable solution compared to relying on users to avoid the triggering behavior.
Fixing something just to get the selftests to pass is fine, but do you actually know of a real-world case where this is a problem that needs to be resolved? That's what I'm asking here, do you have users that have run into this issue? I ask as it's not a regression from what I can determine, but rather a new "feature".
thanks,
greg k-h