** Changed in: linux (Ubuntu)
Status: Invalid => Fix Released
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https://bugs.launchpad.net/bugs/1895132
Title:
s390x broken with unknown syscall number on kernels < 5.8
Status in Ubuntu on IBM z Systems:
Fix Released
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
Bug description:
SRU Justification
Note: I marked this as affecting bionic as well, as discovered in bug
1916485.
Impact: On kernels prior to 5.8 when a task is in traced state (due to
audit, ptrace, or seccomp) s390x and a syscall is issued that the
kernel doesn't know about s390x will not return ENOSYS in r2 but
instead will return the syscall number. This breaks userspace all over
the place. The following program compiled on s390x will output 500
instead of -ENOSYS:
root@test:~# cat test.c
#define _GNU_SOURCE
#include <libgen.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
static inline int dummy_inline_asm(void)
{
register long r1 asm("r1") = 500;
register long r2 asm("r2") = -1;
register long r3 asm("r3") = -1;
register long r4 asm("r4") = -1;
register long r5 asm("r5") = -1;
register long __res_r2 asm("r2");
asm volatile(
"svc 0\n\t"
: "=d"(__res_r2)
: "d"(r1), "0"(r2), "d"(r3), "d"(r4), "d"(r5)
: "memory");
return (int) __res_r2;
}
static inline int dummy_syscall(void)
{
return syscall(500, -1, -1, -1, -1);
}
int main(int argc, char *argv[])
{
printf("Uhm: %d\n", dummy_inline_asm());
printf("Uhm: %d\n", dummy_syscall());
exit(EXIT_SUCCESS);
}
This breaks LXD on s390x currently completely as well as strace.
Fix: Backport
commit cd29fa798001075a554b978df3a64e6656c25794
Author: Sven Schnelle <[email protected]>
Date: Fri Mar 6 13:18:31 2020 +0100
s390/ptrace: return -ENOSYS when invalid syscall is supplied
The current code returns the syscall number which an invalid
syscall number is supplied and tracing is enabled. This makes
the strace testsuite fail.
Signed-off-by: Sven Schnelle <[email protected]>
Signed-off-by: Vasily Gorbik <[email protected]>
which got released with 5.8. The commit missed to Cc stable and
although I've asked Sven to include it in stable I'm not sure when or
if it will show up there.
Regression Potential: Limited to s390x.
Test Case: The reproducer given above needs to output -ENOSYS instead
of 500.
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