I stumbled across a very odd bug that doesn't make much sense to me. I am trying out a new tunable available in glibc-2.35 where I set glibc.malloc.hugetlb=1 https://www.gnu.org/software/libc/manual/html_node/Memory-Allocation-Tunables.html#index-glibc_002emalloc_002ehugetlb With this tunable setting, scanelf, as called by portage, always results in an "unknown syscall" for seccomp. This is way over my head. I have no idea why glibc utilizing hugetlb would have any such effect on a the seccomp syscall. Reproducible: Always
If you try using scanelf by yourself on some binary, does it die? Could you strace it to find out which?
(In reply to Sam James from comment #1) > If you try using scanelf by yourself on some binary, does it die? > > Could you strace it to find out which? Eh, reproduced. > # GLIBC_TUNABLES=glibc.malloc.hugetlb=1 scanelf >Bad system call (core dumped) >openat(AT_FDCWD, "/sys/kernel/mm/transparent_hugepage/hpage_pmd_size", O_RDONLY) = 3 >read(3, "2097152\n", 21) = 8 >close(3) = 0 >brk(NULL) = 0x5615e690f000 >brk(0x5615e6b0f000) = 0x5615e6b0f000 >madvise(0x5615e690f000, 2097152, MADV_HUGEPAGE) = 28 >+++ killed by SIGSYS (core dumped) +++ >Bad system call (core dumped)
glibc is using madvise to record that huge pages are being used. I think madvise is pretty reasonable for us to call. In fact, we've considered adding it to scanelf itself in bug 749624.
The bug has been closed via the following commit(s): https://gitweb.gentoo.org/proj/pax-utils.git/commit/?id=d9f65269d7182ef1d313e3b87bcea37e45958561 commit d9f65269d7182ef1d313e3b87bcea37e45958561 Author: WANG Xuerui <xen0n@gentoo.org> AuthorDate: 2022-04-24 18:41:55 +0000 Commit: WANG Xuerui <xen0n@gentoo.org> CommitDate: 2022-04-25 01:19:39 +0000 seccomp: allow madvise() call (glibc 2.35+) Closes: https://bugs.gentoo.org/836735 Reviewed-by: Sam James <sam@gentoo.org> Signed-off-by: WANG Xuerui <xen0n@gentoo.org> seccomp-bpf.c | 3 +++ seccomp-bpf.h | 76 +++++++++++++++++++++++++++++------------------------------ 2 files changed, 41 insertions(+), 38 deletions(-)
