This fix can be found in Jammy as well, mark this as fix-released.
** Changed in: linux (Ubuntu)
Status: Incomplete => Fix Released
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https://bugs.launchpad.net/bugs/1948351
Title:
ppc64 BPF JIT mod by 1 will not return 0
Status in linux package in Ubuntu:
Fix Released
Status in linux source package in Bionic:
Fix Released
Status in linux source package in Focal:
Fix Released
Status in linux source package in Hirsute:
Fix Released
Status in linux source package in Impish:
Fix Released
Bug description:
[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
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