[PATCH] Introduce the pkill_on_warn boot parameter
From: Alexander Popov <hidden>
Date: 2021-09-29 18:58:43
Also in:
linux-hardening, lkml
Subsystem:
documentation, the rest · Maintainers:
Jonathan Corbet, Linus Torvalds
Currently, the Linux kernel provides two types of reaction to kernel
warnings:
1. Do nothing (by default),
2. Call panic() if panic_on_warn is set. That's a very strong reaction,
so panic_on_warn is usually disabled on production systems.
From a safety point of view, the Linux kernel misses a middle way of
handling kernel warnings:
- The kernel should stop the activity that provokes a warning,
- But the kernel should avoid complete denial of service.
From a security point of view, kernel warning messages provide a lot of
useful information for attackers. Many GNU/Linux distributions allow
unprivileged users to read the kernel log, so attackers use kernel
warning infoleak in vulnerability exploits. See the examples:
https://a13xp0p0v.github.io/2020/02/15/CVE-2019-18683.html
https://a13xp0p0v.github.io/2021/02/09/CVE-2021-26708.html
Let's introduce the pkill_on_warn boot parameter.
If this parameter is set, the kernel kills all threads in a process
that provoked a kernel warning. This behavior is reasonable from a safety
point of view described above. It is also useful for kernel security
hardening because the system kills an exploit process that hits a
kernel warning.
Signed-off-by: Alexander Popov <redacted>
---
Documentation/admin-guide/kernel-parameters.txt | 4 ++++
kernel/panic.c | 5 +++++
2 files changed, 9 insertions(+)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 91ba391f9b32..86c748907666 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt@@ -4112,6 +4112,10 @@ pirq= [SMP,APIC] Manual mp-table setup See Documentation/x86/i386/IO-APIC.rst. + pkill_on_warn= Kill all threads in a process that provoked a + kernel warning. + Format: { "0" | "1" } + plip= [PPT,NET] Parallel port network link Format: { parport<nr> | timid | 0 } See also Documentation/admin-guide/parport.rst.
diff --git a/kernel/panic.c b/kernel/panic.c
index cefd7d82366f..47b728bfb1d3 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c@@ -53,6 +53,7 @@ static int pause_on_oops_flag; static DEFINE_SPINLOCK(pause_on_oops_lock); bool crash_kexec_post_notifiers; int panic_on_warn __read_mostly; +int pkill_on_warn __read_mostly; unsigned long panic_on_taint; bool panic_on_taint_nousertaint = false;
@@ -610,6 +611,9 @@ void __warn(const char *file, int line, void *caller, unsigned taint, print_oops_end_marker(); + if (pkill_on_warn && system_state >= SYSTEM_RUNNING) + do_group_exit(SIGKILL); + /* Just a warning, don't kill lockdep. */ add_taint(taint, LOCKDEP_STILL_OK); }
@@ -694,6 +698,7 @@ core_param(panic, panic_timeout, int, 0644); core_param(panic_print, panic_print, ulong, 0644); core_param(pause_on_oops, pause_on_oops, int, 0644); core_param(panic_on_warn, panic_on_warn, int, 0644); +core_param(pkill_on_warn, pkill_on_warn, int, 0644); core_param(crash_kexec_post_notifiers, crash_kexec_post_notifiers, bool, 0644); static int __init oops_setup(char *s)
--
2.31.1