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Code Issues Releases Activity

Seccomp filter: deal with arch_prctl(ARCH_CET_STATUS, ...).

Browse Source 
The dynamic loader of GNU libc 2.28 uses this system call to
initialize CPU information, see
https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/x86/cpu-features.c;hb=glibc-2.28#l28.
Simulating an older kernel by returning EINVAL should be the most
harmless rule here.

The ARCH_CET_STATUS symbol isn't yet exposed by the kernel headers;
see the FIXME at the top of
https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/x86/include/asm/prctl.h;hb=glibc-2.28.

* lib-src/seccomp-filter.c (ARCH_CET_STATUS): Define if not
already present.  Inline the value because there doesn't seem to
be a header file exporting this constant yet.
(main): Make ARCH_CET_STATUS subfunction of arch_prctl return EINVAL.
This commit is contained in:
Philipp Stephani 2021-04-19 21:10:20 +02:00
parent ab287a148f
commit 27af0a3dc8
1 changed files with 6 additions and 0 deletions
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6
lib-src/seccomp-filter.c
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@ -60,6 +60,10 @@ variants of those files that can be used to sandbox Emacs before
#include "verify.h"
#ifndef ARCH_CET_STATUS
#define ARCH_CET_STATUS 0x3001
#endif
static ATTRIBUTE_FORMAT_PRINTF (2, 3) _Noreturn void
fail (int error, const char *format, ...)
{
@ -345,6 +349,8 @@ main (int argc, char **argv)
RULE (SCMP_ACT_ALLOW, SCMP_SYS (set_tid_address));
RULE (SCMP_ACT_ALLOW, SCMP_SYS (arch_prctl),
SCMP_A0_32 (SCMP_CMP_EQ, ARCH_SET_FS));
RULE (SCMP_ACT_ERRNO (EINVAL), SCMP_SYS (arch_prctl),
SCMP_A0_32 (SCMP_CMP_EQ, ARCH_CET_STATUS));
RULE (SCMP_ACT_ALLOW, SCMP_SYS (statfs));
/* We want to allow starting the Emacs binary itself with the