On 5/28/24 7:57 PM, Johannes Berg wrote: > On Tue, 2024-05-28 at 18:16 +0800, Tiwei Bie wrote: >> On 5/28/24 4:54 PM, benja...@sipsolutions.net wrote: >>> From: Benjamin Berg <benjamin.b...@intel.com> >>> >>> Newer glibc versions are enabling rseq support by default. This remains >>> enabled in the cloned child process, potentially causing the host kernel >>> to write/read memory in the child. >>> >>> It appears that this was purely not an issue because the used memory >>> area happened to be above TASK_SIZE and remains mapped. >> >> I also encountered this issue. In my case, with "Force a static link" >> (CONFIG_STATIC_LINK) enabled, UML will crash immediately every time >> it starts up. I worked around this by setting the glibc.pthread.rseq >> tunable via GLIBC_TUNABLES [1] before launching UML. >> >> So another easy way to work around this issue without introducing runtime >> overhead might be to add the GLIBC_TUNABLES=glibc.pthread.rseq=0 environment >> variable and exec /proc/self/exe in UML on startup. >> > > It's also a bit of a question what to rely on - this would introduce a > dependency on glibc behaviour, whereas doing the double-clone proposed > here will work purely because of host kernel behaviour, regardless of > what part of the system set up rseq, how the tunables work, etc.
Makes sense. My previous concern was primarily about the runtime overhead, but after taking a closer look at the patch, I realized that the double-clone won't happen on the critical path, so there shouldn't be any performance issues. I also think the double-clone proposal is better. :) Regards, Tiwei
