** Description changed: + [Impact] + When doing MOD by 1 with a immediate/constant divisor on PPC, the JIT will produce code that returns the dividend, just like a division, instead of 0. + + Both eBPF and cBPF will fail as well when doing such operations. + + [Test case] + $ cat bpf-mod1.c + #include <linux/bpf.h> + #include <unistd.h> + #include <sys/syscall.h> + #include <sys/socket.h> + #include <stdio.h> + #include <sys/prctl.h> + #include <stdlib.h> + #include <errno.h> + #include <limits.h> + #include <err.h> + #include <string.h> + #include <linux/filter.h> + + #define ARRAY_SIZE(array) (sizeof(array)/sizeof(array[0])) + + static int pair[2]; + + static int attach() + { + int r; + + struct sock_filter insn[] = { + { BPF_LD | BPF_W | BPF_ABS, 0, 0, 0 }, + { BPF_ALU | BPF_MOD, 0, 0, 1 }, + { BPF_RET | BPF_A, 0, 0, 0 }, + }; + + struct sock_fprog prog = {}; + prog.filter = insn; + prog.len = ARRAY_SIZE(insn); + + socketpair(AF_UNIX, SOCK_DGRAM, 0, pair); + setsockopt(pair[1], SOL_SOCKET, SO_ATTACH_FILTER, &prog, sizeof(prog)); + return 0; + } + + int main(int argc, char **argv) + { + int buf[5]; + int r; + r = attach(); + if (r < 0) { + err(1, "function will error out already"); + } + write(pair[0], "hello", 5); + r = recv(pair[1], buf, 5, MSG_DONTWAIT); + if (r != -1 || errno != EAGAIN) { + err(1, "program failed"); + } + return 0; + } + $ gcc -o bpf-mod1 bpf-mod1.c + $ ./bpf-mod1 + cbpf-mod1: program failed: Success + + After fix: + $ ./bpf-mod1 + $ echo $? + 0 + + [Potential regression] + BPF programs might be misbehave on ppc64el. + + ======================================================== + This is a scripted bug report about ADT failures while running linux tests for linux/5.4.0-90.101 on focal. Whether this is caused by the dep8 tests of the tested source or the kernel has yet to be determined. - Consistently failing on Focal/linux 5.4.0-90.101 13:15:26 DEBUG| [stdout] # selftests: net: test_bpf.sh 13:15:27 DEBUG| [stdout] # test_bpf: [FAIL] 13:15:27 DEBUG| [stdout] not ok 9 selftests: net: test_bpf.sh # exit=1 - Testing failed on: ppc64el: https://autopkgtest.ubuntu.com/results/autopkgtest-focal/focal/ppc64el/l/linux/20211021_141544_eda49@/log.gz
-- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1948351 Title: ppc64 BPF JIT mod by 1 will not return 0 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1948351/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs