During investigation of an Alpha specific problem in GNU Emacs
(see https://bugs.gentoo.org/660448 and https://debbugs.gnu.org/32083)
we found that on Alpha the ADDR_NO_RANDOMIZE flag set with
personality(2) is not preserved across execve(2).
The following test program demonstrates the problem:
-------- 8< --------
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/personality.h>
int
main (int argc, char **argv)
{
int pers, new_pers;
if ((pers = personality (0xffffffff)) < 0) {
fprintf (stderr, "could not get personality\n");
exit (1);
}
if (getenv ("WAS_HERE")) {
printf ("*** after execvp ***\n");
printf ("personality = 0x%08x\n", pers);
exit (0);
}
printf ("old personality = 0x%08x\n", pers);
new_pers = pers | ADDR_NO_RANDOMIZE;
printf ("demand personality = 0x%08x\n", new_pers);
if (personality (new_pers) < 0) {
fprintf (stderr, "could not set personality\n");
exit (1);
}
if ((pers = personality (0xffffffff)) < 0) {
fprintf (stderr, "could not get personality\n");
exit (1);
}
printf ("new personality = 0x%08x\n", pers);
putenv ("WAS_HERE=1");
execvp (*argv, argv);
fprintf (stderr, "execvp returned\n");
exit (1);
}
-------- >8 --------
I get as output (on Alpha, kernel 4.17.0):
old personality = 0x00000000
demand personality = 0x00040000
new personality = 0x00040000
*** after execvp ***
personality = 0x00000000
Whereas on amd64 the last line is (as should be expected):
personality = 0x00040000
I suspect that the problem is with the SET_PERSONALITY macro defined
in arch/alpha/include/asm/elf.h:
#define SET_PERSONALITY(EX) \
set_personality(((EX).e_flags & EF_ALPHA_32BIT) \
? PER_LINUX_32BIT : PER_LINUX)
The corresponding code for other architectures (e.g., ppc) does
additional masking of the flag bits, like this:
set_personality(PER_LINUX | (current->personality & (~PER_MASK)))
Linux monolith 4.17.0+ #43 SMP Wed Jun 6 10:42:37 CEST 2018 alpha EV68AL
Tsunami GNU/Linux
GNU C 7.3.0
GNU Make 4.2.1
Binutils 2.30
Util-linux 2.32
Mount 2.32
Module-init-tools 25
E2fsprogs 1.44.2
Linux C Library 2.27
Dynamic linker (ldd) 2.27
Linux C++ Library 6.0.24
Procps 3.3.15
Net-tools 1.60
Kbd 2.0.4
Console-tools 2.0.4
Sh-utils 8.30
Udev 238
Modules Loaded binfmt_misc cdrom libata netlink_diag pata_ali sr_mod
unix_diag
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