On 29.09.2021 21:58, Alexander Popov wrote: > 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 <alex.popov@xxxxxxxxx> This patch was tested using CONFIG_LKDTM. The kernel kills a process that performs this: echo WARNING > /sys/kernel/debug/provoke-crash/DIRECT If you are fine with this approach, I will prepare a patch adding the pkill_on_warn sysctl. Best regards, Alexander > --- > 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) >
